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Why do we anthromorphize evolution and genes and nature?

Why do we anthromorphize evolution and genes and nature?


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Books sometimes says things "Our genes want us to have as many children as possible", or "Evolution wants the fittest to survive". But genes are not conscious entities who can want things. So, why do we anthromorphize genes, evolution, and nature? I apologize if this question is not appropriate for this This Site. Perhaps it can be moved to an appropriate This Site if it is.


The evolutionary history of men and women should not prevent us from seeking gender equality

Beatrice Alba does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.

Partners

La Trobe University provides funding as a member of The Conversation AU.

The Conversation UK receives funding from these organisations

Compared to women, men are more aggressive and enjoy being promiscuous.

These are just two examples of the sorts of statements that are linked to research findings from evolutionary psychologists.

If such conclusions are accurate, it raises concerns that our biology might prevent us from progressing towards gender equality. But I argue this is not the case, and that we need to understand our evolutionary history in order to overcome gender inequality.


The Scientific Method

Overview

An example of oversimplification that confounds many students of biology (particularly early in their studies) is the use of language that hides the experimental process used to build knowledge. For the sake of expediency we often tell stories about biological systems as if we are presenting unquestionable facts. However, while we often write and speak about topics in biology with a conviction that gives the appearance of "factual" knowledge, reality is often more nuanced and filled with significant uncertainties. The "factual" presentation of material (usually lacking discussion of evidence or our degree of confidence in the evidence) plays to our natural tendency to feel good about "knowing" things but it tends to create a false sense of security in the state of knowledge and does little to encourage the use of imagination or the development of critical thinking.

A better way to describe our knowledge about the natural world would be to explicitly qualify that the knowledge presented represents our current best understanding that has not yet been refuted by experiment. Unfortunately, repeated qualification becomes rather cumbersome. The important thing to remember is that while we may not say so explicitly, all of the knowledge we discuss in class represents only the best of our current understanding. Some ideas have withstood repeated and varied experimentation while other topics have yet to be tested as thoroughly. So if we're not as certain about things as we'd like to believe sometimes, how do we know what to put confidence in and what to be skeptical of. The complete answer is non-trivial but it begins with developing an understanding of the process we use in science to build new knowledge. The scientific method is the process by which new knowledge is developed. While the process can be described with long lists of "steps" (often seen in textbooks), its core elements can be described more succinctly.

Succinct Description of Scientific Method (adapted from Feynman)

  1. Make an observation about the world.
  2. Propose a possible explanation for the observation.
  3. Test the explanation by experiment.
  4. If the explanation disagrees with experiment, the explanation is wrong.

At its core, that's it! In science there may be multiple simultaneously proposed explanations or ideas that are tested by experiment. The ideas that fail experimentation are left behind. The ideas that survive experimentation move forward and are often retested by alternative experiments until they too either fail or continue to be retained.

Making an observation and asking a question

The ability to make useful observations and/or ask meaningful questions requires curiosity, creativity and imagination &ndash this cannot be over-stated. Indeed, historically, it is first and foremost the application of these skills, perhaps more than technical ability, which has led to big advances in science. Many people think that making meaningful observations and asking useful questions is the easiest part of the scientific method. This is not the case. Why? Perceiving what other people have not perceived before, and coming up with possible explanations, takes work, imagination, creativity, and thoughtful reflection! In addition, our senses of observation are often biased by life-experience, prior knowledge, or even our own biology. These underlying biases influence how we see the world, how we interpret what we see, and what we are ultimately curious about. This means that when we look at the world, we can miss a lot of things that are actually right under our noses. Douglas Adams, who is best known for his book The Hitchhiker&rsquos Guide to the Galaxy, once expanded on this point by writing:

&ldquoThe most misleading assumptions are the ones you don't even know you're making.&rdquo

Scientists, therefore, need to be aware of any underlying biases and any assumptions that may influence how they internalize and interpret observations. This includes approaching the variety of places we get our knowledge (i.e. textbooks, instructors, the Internet) with a healthy dose of skepticism. We need to learn to examine the evidence underling the &ldquofacts&rdquo we supposedly know and make critical judgments about how much we trust that knowledge. More generally, taking the time to make careful observations and to uncover any assumptions and biases that could influence how they are interpreted is, therefore, time well spent. This skill, like all others, needs to be developed and takes practice and we&rsquoll try to start you on this in BIS2A.

For fun, and to test your observation skills, Google &ldquoobservation tests&rdquo. Many of the search results will take you to interesting psychological tests and/or videos that illustrate how difficult accurate observation can be.

Generating a testable hypothesis

The "possible explanation" referred to in step 3 above has a formal name it is called a . A hypothesis is not a random guess. A hypothesis is an educated (based on prior knowledge or a new viewpoint) explanation for an event or observation. It is typically most useful if the hypothesis can be tested. This requires that the tools to make informative measurements on the system exist and that the experimenter has sufficient control over the system in question to make the necessary observations.

Most of the time, behaviors of the system that the experimenter wants to test can be influenced by many factors. We call the behaviors and factors, dependent and independent variables, respectively. The dependent variable is the behavior that needs explaining while the independent variables are all of the other things that might change and influence the behavior of the dependent variable. For example, an experimenter that has developed a new drug to reduce blood pressure would want to test whether her new drug actually influences blood pressure (i.e., "Does blood pressure depend on the dose of this drug?" or "Is there a negative correlation between the dose of this drug and blood pressure"). In this example, the system is the human body, the dependent variable might be blood pressure, and one independent variable (among the many other independent variables that might affect blood pressure- diet, stress, physical activity, age. ) would be the dose of drug. The null hypothesis might be that the new drug has no effect on blood pressure, and the alternative hypothesis is that the drug affects blood pressure. In a well-designed experiment the investigator must either have excellent control over the number of independent variables (for example, this drug efficacy experiment would be easier to do with a set of genetically identical mice raised identically and tested in identical environments- but are mice are mice a good model for the vascular physiology and biochemistry of humans?), or the investigator their best to randomly distribute the test drug among a very large population of humans that reflect all possible aspects of the "independent variables" that the investigator cannot control.

In this class, most of what we discuss (but not all) will be hypotheses that have SUBSTANTIAL experimental backing. You may have heard that a hypothesis that has withstood the test of many experimental observations is dignified with the term "theory". Some theories and the hypotheses are so well tested that they are no longer referred to as theories at all, but are accepted as incontrovertable facts. For example, at one time the hypothesis that DNA carried the information required for heredity was debatable- other hypotheses were equally plausible. But no one refers to DNA (sometimes RNA) = biological heredity as a "theory" anymore. It is, frankly, accepted as incontrovertible "fact", or "dominant paradigm". The DNA <-> RNA -> protein universal mechanism for information expression is actually termed the "Central Dogma".

Overthrowing a dominant paradigm is certainly one of the most useful things a scientist can do, but a scientist that is so inclined would need to choose their battles wisely.

Note: For more on dependent and independent variables

In BIS2A, and beyond, we prefer to avoid using language like &ldquothe experiment proved her hypothesis&rdquo when referring to a case like the blood pressure example above. Rather we would say, if there is significant negative correlation between blood pressure and drug dose, &ldquothe experiment is consistent with her hypothesis". For convenience (one of the language shortcuts we discussed earlier). It would be more correct to state, &ldquothe experiment falsified her null hypothesis and is consistent with her alternative hypothesis.&rdquo

What does the statement about falsifying hypotheses mean in your own words? Why is falsification critical to the scientific method? In the drug vs. blood pressure example discussed above, what is the null hypothesis?

Controls

In an ideal case, an experiment will include what are known as control groups. Control groups are experimental conditions in which the values of the independent variables (there may be more than one) are maintained as close to those in the experimental group with the exception of the independent variable being tested. In the blood pressure example, an ideal scenario would be to have one identical group of people taking the drug and another group of people identical to those in the experimental group taking a pill containing something known to not influence blood pressure. In this oversimplified example, all independent variables are identical in the control and experimental groups with the exception of the presence or absence of the new drug. Under these circumstances, if the value of the dependent variable (blood pressure) of the experimental group differs from that of the control group, one can reasonably conclude that the difference must be due to the difference in independent variable (the presence/absence of the drug). This is, of course, the ideal. In real life we also need to determine whether the difference between the control and test groups is significant, or due to other uncontrolled difference between our two groups. Statistics will be required to determine whether and differences are significant. You won&rsquot need to understand the nuances of these statistical issues in BIS2A, but if you're going to become a scientist, or doctor, or even a good citizen, some knowledge of statistics will be required- make sure you take a course while you're here!

Accuracy in Measurement, Uncertainty, and Replication

Finally, we mention the intuitive notion that the tools used to make the measurements in an experiment must be reasonably accurate. How accurate? They must be accurate enough to make measurements with sufficient certainty to draw conclusions about whether changes in independent variables actually influence the value of a dependent variable. If we take, yet again, the blood pressure example above. In that experiment we made the important assumption that the experimenter had tools that allowed her to make accurate measurements of the changes in blood pressure associated with the effects of the drug. For instance if the changes associated with the drug ranged between 0 and 3 mmHg and her meter capably measured changes in blood pressure with a certainty of +/- 5 mmHg she could not have made the necessary measurements to test her hypothesis or would have missed seeing the effect of the drug. For the sake of example, we assume that she had a better instrument and that she could be confident that any changes she measured were indeed differences due to the drug treatment and that they were not due to measurement error, sample-to-sample variability, or other sources of variation that lower the confidence of the conclusions that are drawn from the experiment.

The topic of measurement error leads us to mention that there are numerous other possible sources of uncertainty in experimental data that you as students will ultimately need to learn about. These sources of error have a lot to do with determining how certain we are that experiments have disproven a hypothesis, how much we should trust the interpretation of the experimental results and by extension our current state of knowledge. Even at this stage, you will recognize some experimental strategies used to deal with these sources of uncertainty (i.e. making measurements on multiple samples creating replicate experiments). You will learn more about this in your statistics courses later on.

For now, you should, however, be aware that experiments carry a certain degree of confidence in the results and that the degree of confidence in the results can be influenced by many factors. Developing healthy skepticism involves, among other things, learning to assess the quality of an experiment and the interpretation of the findings and learning to ask questions about things like this. A good scientist has a good sense of how well-supported (by experimental evidence) their current, working models for various processes are.

After moving to California to attend UC Davis, you have fallen in love with fresh tomatoes. You decide that the tomatoes in the stores just don&rsquot taste right and resolve to grow your own.

You plant tomato plants all over your back yard every free space now has a freshly planted tomato seedling of the same variety. You have planted tomatoes in the ground in full sunlight and next to your house in full shade.

Observation: After the first year of harvest, you make the observation that the plants growing in full shade almost always seem shorter than those in the full sun. You think that you have a reasonable explanation (hypothesis) for this observation.

Based on the information above, you create the following hypothesis to explain the differences in height you noticed in your tomatoes:

Hypothesis: The height that my tomato plants reach is positively correlated to the amount of sunlight they are exposed to (e.g. the more sun the plant gets the taller it will be).

This hypothesis is testable and falsifiable. So, the next summer you decide to test your hypothesis.

This hypothesis also allows you to make a prediction. In this case you might predict that IF you were to shade a set of tomatoes in the sunny part of the yard, THEN those plants would be shorter than their full-sun neighbors.

You design an experiment to test your hypothesis by buying the same variety of tomato that you planted the previous year and plant your whole yard again. This year, however, you decide to do two different things:

  1. You create a shade structure that you place over a small subset of plants in the sunny part of your yard.
  2. You build a contraption with mirrors that redirects some sunlight onto a small subset of plants that are in the shady part of the yard.
  • Question 1: We used a shortcut above. Can you create statements for both the null and alternative hypothesis? Work with your classmates to do this.
  • Question 2: Why do you create a shade structure? What is this testing? Based on your hypothesis what do you predict will happen to the plants under the shade structure?
  • Question 3: Why do you create the mirror contraption? Why do you potentially need this contraption if you already have the shade structure?
  • New Data: At the end of the summer you measure the height of your tomato plants and you find once again that the plants in the sunny part of the yard are indeed taller than those in the shady part of the yard. However, you notice that there is no difference in height between the plants under your shade structure and those right next to the structure in full sun. In addition, you notice that the plants in the shady part of the yard are all about the same height, including those that had extra light shined on them via your mirror contraption.
  • Question 4: What does this experiment lead you to conclude? What would you try to do next?
  • Question 5: Imagine an alternative scenario in which you discovered, as before, that the plants in the sunny part of the yard were all the same height (even those under your shade structure) but that the plants in the shady part of the yard that got &ldquoextra&rdquo light from your mirror contraption grew taller than their immediate neighbors. What would this say about your alternate hypothesis? Null hypothesis? What would you do next?
  • Question 6: What assumptions are you making about the ability to make measurements in this experiment? What influence might these assumptions have on your interpretation of the results?


In this class you will occasionally be asked to create a hypothesis, to interpret data, and to design experiments with proper controls. All of these skills take practice to master, we can start to practice them in BIS2A. Again, while we don&rsquot expect you to be masters after reading this text, we will assume that you have read this text during the first week and that the associated concepts are not completely new to you. You can always return to this text as a resource to refresh yourself.

Disclaimer

While the preceding treatment of the experimental method is very basic - you will undoubtedly add numerous layer of sophistication to these basic ideas as you continue in your studies &ndash it should serve as a sufficient introduction to the topic for BIS2A. The most important point to remember from this section is that the knowledge represented in this course, while sometimes inadvertently represented as irrefutable fact, is really just the most current hypothesis about how certain things happen in biology that has yet to be falsified via experiment.


George C. Williams (1926–2010)

Incisive thinker who influenced a generation of evolutionary biologists.

In 1978, at the age of 52, the great evolutionary theorist George C. Williams began to chronicle his own senescence, recording once a year how long it took to run 1,700 metres round a track in Stony Brook, New York. Williams presented the graph of his 12 years of slowing speed at his acceptance speech for the Crafoord Prize in Bioscience that he shared with Ernst Mayr and John Maynard Smith in 1999. He later published it in The Quarterly Review of Biology, with which he was involved for 32 years. The plot encapsulated his lifelong fascination: why do we decline with age?

Williams died on 8 September, aged 84. Little known to the public, this tall, reserved man with an Abraham Lincoln beard will be remembered by evolutionary biologists as one of the most incisive thinkers of the twentieth century. His major contribution, the theory of gene-level natural selection, left a profound and enduring stamp on fields from sociobiology and evolutionary psychology to behavioural ecology. He spoke slowly and little, but when he spoke, you listened: his words were full of insight and flashes of dry wit.

After a stint in the US Army, working on a water purification plant in Italy during the Second World War, Williams finished his BA in zoology at the University of California, Berkeley in 1949. He got his PhD from the University of California, Los Angeles in 1955 for work on the ecology of the blenny — a type of fish. There followed a postdoc at the University of Chicago and an assistant professorship at Michigan State University. In 1960, Williams moved to the State University of New York at Stony Brook. He later became one of the first professors in its newly formed Department of Ecology and Evolution. There he remained until his retirement in 1990 — the year I arrived as assistant professor and inherited his freezer of Icelandic eel samples. He had spent two sabbaticals in Iceland, was fluent in Icelandic and published on the European and American species of eels and their potential hybrids on Iceland.

“He spoke slowly and little, but when he spoke, you listened: his words were full of insight and flashes of dry wit.”

In 1957, he published his seminal paper 'Pleiotropy, Natural Selection, and the Evolution of Senescence' in the journal Evolution. He argued that genes that enhance fitness early in life but have detrimental effects later in life — genes with 'antagonistic pleiotropic effects' — would be expected to persist and even increase in abundance as long as, on balance, they boost an individual's fitness. He also pointed out that selection should be weaker in older age because fewer individuals are alive to be subject to it — an idea for which Williams shares credit with Peter Medawar.

The dominant narrative of early 1960s evolutionary biology was that natural selection acts at the level of the group or even for 'the good of the species'. Even death was explained in a group-selectionist light — as creating space for the next generation. Williams skewered this thinking, which he felt was “sloppy” and “anti-Darwinian”, in his most influential book, Adaptation and Natural Selection (1966). In it he proposed that natural selection almost always acts more directly, swiftly and strongly at the level of the gene or the individual than at the level of the group or even species. He also railed against 'pan-adaptationism' — the idea that every feature is adaptive: he showed that adaptations have to have fitness-enhancing effects at the level of the individual rather than at the level of the species.

Adaptation and Natural Selection was way ahead of its time its impact was felt for decades. Following Williams, E. O. Wilson extended gene-level and individual selection in Sociobiology: The New Synthesis — his controversial 1975 book on the role of genetics in social behaviour, even of humans. And Richard Dawkins's 1976 book The Selfish Gene popularized some of Williams's ideas. That said, gene-level selection and inclusive fitness were not universally accepted then, and still meet with occasional criticism — notably from researchers trying to explain altruism and eusociality, for example. These ideas remain, nonetheless, cornerstones of modern biological theory.

Competition not cooperation

Williams made further influential contributions. With his 1975 book Sex and Evolution, he was among the first to offer explanations for the puzzling prevalence of sexual reproduction. He pointed out that it is yet another example of competition, not cooperation, being the dominant force in evolution — with genes from each parent battling for influence within the same genome. (He saw a bright future for the fields of genetic imprinting and epigenetics.)

Williams went even further with his reductionist view of natural selection in Natural Selection: Domains, Levels and Challenges, his 1992 book about information and matter. He pointed out that what is of importance in evolution is the information that is contained in genes, genotypes and gene pools, not the physical objects — a position reminiscent of Dawkins's 'meme' concept.

Williams returned late in life to his abiding concern — ageing. In 1994 he wrote the book Why We Get Sick: the New Science of Darwinian Medicine with the physician Randolph Nesse. Williams and Nesse proposed that disease symptoms should be understood, and treatment informed, by the long evolutionary history that shaped immune responses. Their work has spawned a new field of study, evolutionary medicine.

It is a cruel irony that this brilliant man who first explained senescence died of Alzheimer's disease.


Mutation, Not Natural Selection, Drives Evolution

In a cavernous concert hall, before an eager audience of thousands, Masatoshi Nei is experiencing a technical glitch.

The biologist has just received Japan’s prestigious Kyoto Prize in Basic Sciences, honoring his groundbreaking exploration of evolution on a molecular level. The eyes and ears of international media, diplomats and dignitaries, including Japan’s Princess Takamado, are trained on the soft-spoken 82-year-old as he delivers his acceptance speech.Or tries to. On a massive screen above him, a slide show advances and retreats randomly as Nei attempts to present techniques he pioneered that have revolutionized his field — and theories that challenge some of its most deeply rooted ideas.

“So sorry,” Nei tells his audience with an endearing chuckle. “I’m always pursuing the theory, not the practical.”

Practicality has been, however, a guiding force throughout Nei’s career, from his early agricultural research to his decades-long quest to move evolutionary biology away from subjective field observations and into objective, math-based analysis on a molecular level. In 1972, he devised a now widely used formula, Nei’s standard genetic distance, which compares key genes of different populations to estimate how long ago the groups diverged. In the early ’90s, Nei was a co-developer of free software that creates evolutionary trees based on genetic data. Two decades later, Molecular Evolutionary Genetics Analysis, or MEGA, remains one of the most widely used and cited computer programs in biology.

But it’s his natural selection-busting theory, which Nei developed in the ’80s and expanded on in the 2013 book Mutation-Driven Evolution, that the researcher wants to see embraced, cited and taught in schools.

A few days after his presentation slides finally cooperated, Nei, director of the Institute of Molecular Evolutionary Genetics at Pennsylvania State University, spoke with Discover about where he believes Darwin went wrong.

Discover : You began your academic career in Japan in the ’50s as an assistant professor of agricultural science. How did you, no pun intended, evolve into a molecular biologist taking on Darwin?

Masatoshi Nei: I wanted to make population genetics useful and practical, so I went into plant breeding. But I started to ask, why does phenotopic [observable trait-based] evolution take place? I was interested in it on a genetic level. Charles Darwin said evolution occurs by natural selection in the presence of continuous variation, but he never proved the occurrence of natural selection in nature. He argued that, but he didn’t present strong evidence.

But among the people working on evolution, most of them still believe natural selection is the driving force.

If you say evolution occurs by natural selection, it looks scientific compared with saying God created everything. Now they say natural selection created everything, but they don’t explain how. If it’s science, you have to explain every step. That’s why I was unhappy. Just a replacement of God with natural selection doesn’t change very much. You have to explain how.

A: Every part of our body is controlled by molecules, so you have to explain on a molecular level. That is the real mechanism of evolution, how molecules change. They change through mutation. Mutation means a change in DNA through, for example, substitution or insertion [of nucleotides]. First you have to have change, and then natural selection may operate or may not operate. I say mutation is the most important, driving force of evolution. Natural selection occurs sometimes, of course, because some types of variations are better than others, but mutation created the different types. Natural selection is secondary.

Q: Someone on the outside looking in at the debate might say you and other researchers are splitting hairs, that both mutation and natural selection drive evolution. How do you respond?

A: I don’t study the character or the function I study the gene that controls it. My position is mutation creates variation, then natural selection may or may not operate, it may or may not choose the good variation and eliminate the bad one, but natural selection is not the driving force.

In neo-Darwinism, evolution is a process of increasing fitness [in the sense of an organism’s ability both to survive and to reproduce]. In mutation-driven evolutionary theory, evolution is a process of increasing or decreasing an organism’s complexity. We tend to believe natural selection selects one type. But there are many types, and still they’re OK. They can survive, no problem.

For example, if blue eyes are better for some reason in Scandinavia, that mutation has a selected advantage, and then of course that advantage will occur more in that population. But first you have to have the mutation. And natural selection itself is not so clear. In certain cases it is, but not always. The gene frequency of blue eyes may have increased by chance, too, rather than natural selection. The blue eye color may be just as good as green. Both can see.

Q: In 1968, your friend and mentor Motoo Kimura proposed the neutral theory of molecular evolution, arguing that most mutations that occur have neither advantageous nor deleterious consequences for an organism. How did you take neutral theory a step further with mutation-driven evolutionary theory?

A: Kimura believed morphology [appearance] evolves through natural selection. He applied neutral theory only on a molecular level. I say it can determine morphological characteristics as well because DNA determines everything, but to prove this has not been so easy. [Laughs.] Forty or 50 years later, I am still trying to prove it.

Q: One of your most significant contributions to the field is Nei’s standard genetic distance, a formula that determines when different populations diverged based on mathematical analysis of their genomes. But this formula assumes the rate of genetic change is constant. Do you think human activity — from overfishing to burning fossil fuels to illuminating our cities and highways with artificial light — could be speeding up the rate of mutation?

A: I think there is a mutagenic element to human activity, but it’s difficult to gather proof. It’s occurred only in, say, the past 10,000 years, and I don’t know if it’s changing the rate of mutation. You can identify how many different mutations occurred, but not always how.

Q: You’ve been talking about mutation-driven evolution for more than three decades. Why do you think the majority of evolutionary biologists remain in the natural selection camp?

A: I expressed this simple view first in 1975 in my book Molecular Population Genetics and Evolution , and in 1987 in a chapter in another book, but no one changed their views or the textbooks. Of course, at that time, molecular biology had not developed too far yet, and traditional evolutionary biology only considered morphology, not how the variation occurred.

Some birds, for example, have a variant of hemoglobin that allows them to fly over the Himalayas, at very high altitudes. Some alligators have a different variant of hemoglobin that allows them to stay submerged for a very long time. This has been known for a while and everyone felt, well, variation exists in the populations, but the condition necessary must be just natural selection.

Q: In 1987, you co-authored a paper with Naruya Saitou describing the neighbor-joining method, a novel algorithm for creating evolutionary trees by working backward based on key genetic differences between related species, the idea being the more recently one species diverged from another, the more similar their DNA will be. It’s been cited more than 34,000 times over the years and has become a cornerstone of molecular evolutionary biology research. Why do you feel it was so influential?

A: It’s simple. [Laughs.] I had developed the genetic distance theory [in the ’70s] because I wanted to make a phylogenetic tree, and distance can be used for making trees. But I was also interested in statistics. So I combined the two methods. To test it, first we did computer simulations: We generated a DNA sequence for an evolutionary tree where we already knew where the tree branched. Then we used statistics, the neighbor-joining method, to reconstruct the tree and test whether it resembled the actual phylogenetic tree. It did, and that’s how we knew this method gave a pretty good idea of how species evolved and diverged.

At first, other biologists were fanaticists about sticking to earlier methods of calculating relationships between species. There were a lot of stupid fights in the ’80s, but I insisted it would work. In the case of, say, using 100 genetic sequences, we can make a neighbor-joining tree within a few seconds. With the regular method, it would take months. And after working for months, the result was almost always the same as the neighbor-joining method.

Q: You’ve stated on a number of occasions that you’re ready for a lot of criticism over your most recent book, 2013’s Mutation-Driven Evolution . Why?

A: I presented such views in my 1987 book Molecular Evolutionary Genetics , but people didn’t pay attention. Textbooks on evolution haven’t changed: They still say natural selection causes evolution. My views were totally ignored. In that book, I discussed many statistical techniques, and only in the last chapter did I discuss the problem of natural selection not being proven. The chapter did not convince a lot of people, I think, because they already had a preconceived notion that natural selection must be the driving force because Darwin said so. Darwin is a god in evolution, so you can’t criticize Darwin. If you do, you’re branded as arrogant.

But any time a scientific theory is treated like dogma, you have to question it. The dogma of natural selection has existed a long time. Most people have not questioned it. Most textbooks still state this is so. Most students are educated with these books.

You have to question dogma. Use common sense. You have to think for yourself, without preconceptions. That is what’s important in science.

This article originally appeared in print as "We Are All Mutants."


How do we know that evolution is really happening?

Evolution is one of the greatest theories in all of science. It sets out to explain life: specifically, how the first simple life gave rise to all the huge diversity we see today, from bacteria to oak trees to blue whales.

For scientists, evolution is a fact. We know that life evolved with the same certainty that we know the Earth is roughly spherical, that gravity keeps us on it, and that wasps at a picnic are annoying.

Not that you would know that from the media in some countries, where evolution is ferociously argued about &ndash put down as "just a theory" or dismissed as a flat-out lie.

Why are biologists so certain about this? What is the evidence? The short answer is that there is so much it's hard to know where to start. But here is a very cursory summary of the evidence that life has, indeed, evolved.

It might help to first spell out quickly what Darwin's theory of evolution actually says. Most of us have the general idea: species change over time, only the fittest survive, and somehow a monkey-like creature gave rise to human beings.

It is hard to accept that you are descended, through countless generations, from a worm

Darwin's theory of evolution says that each new organism is subtly different from its parents, and these differences can sometimes help the offspring or impede it. As organisms compete for food and mates, those with the advantageous traits produce more offspring, while those with unhelpful traits may not produce any. So within a given population, advantageous traits become common and unhelpful ones disappear.

Given enough time, these changes mount up and lead to the appearance of new species and new types of organism, one small change at a time. Step by step, worms became fish, fish came onto land and developed four legs, those four-legged animals grew hair and &ndash eventually &ndash some of them started walking around on two legs, called themselves "humans" and discovered evolution.

This can be hard to believe. It's one thing to realise that you are not identical to our parents: perhaps your hair is a different colour, or you are taller, or have a more cheerful nature. But it is much harder to accept that you are descended, through countless generations, from a worm.

Plenty of people certainly don't accept this. But forget all the drama for a moment. Instead, begin as Charles Darwin did: on your doorstep.

Darwin's book On the Origin of Species, first published in 1859, begins by asking the reader to look around at the familiar. Not unexplored tropical islands or faraway jungles, but the farmyard and garden. There, you can easily see that organisms pass on characteristics to their offspring, changing the nature of that organism over time.

These changes from generation to generation are called "descent with modification"

Darwin was highlighting the process of cultivation and breeding. For generations, farmers and gardeners have purposefully bred animals to be bigger or stronger, and plants to yield more crops.

Breeders work just like Darwin imagined evolution worked. Suppose you want to breed chickens that lay more eggs. First you must find those hens that lay more eggs than the others. Then you must hatch their eggs, and ensure that the resulting chicks reproduce. These chicks should also lay more eggs.

If you repeat the process with each generation, eventually you'll have hens that lay far more eggs than wild chickens do. A female jungle fowl &ndash the closest wild relative of the domestic chicken &ndash might lay 30 eggs in a year, whereas farm hens may well produce ten times as many.

These changes from generation to generation are called "descent with modification".

Our oldest domesticated animals are still capable of rapid improvement or modification

A young chick will in many ways be similar to its parents: it will be recognisably a chicken, and definitely not an aardvark, and it will probably be more similar to its parents than it is to other chickens. But it won't be identical.

"That's what evolution is," says Steve Jones of University College London in the UK. "It's a series of mistakes that build up."

You might think that breeding can only make a few changes, but there seems to be no end to it. "No case is on record of a variable being ceasing to be variable under cultivation," wrote Darwin. "Our oldest cultivated plants, such as wheat, still often yield new varieties: our oldest domesticated animals are still capable of rapid improvement or modification."

Breeding, Darwin argued, is essentially evolution under human supervision. It shows us that the tiny changes from generation to generation can add up. "It's inevitable," says Jones. "It's bound to happen."

Still, it's quite a step from carefully breeding chickens that lay more eggs to the natural evolution of new species. According to evolutionary theory, those chickens are ultimately descended from dinosaurs, and if you go further back, from fish.

The answer is simply that evolution takes a long time to make big changes. To see evidence of that, you have to look at older records. You have to look at fossils.

Fossils are the remains of long-dead organisms, preserved in rock. Because rocks are laid down in layers, one on top of the other, the fossil record is generally set out in date order: the oldest fossils are at the bottom.

I always think that the most convincing case for evolution is in the fossil record

Running through the fossil record makes it clear that life has changed over time.

The oldest fossils of all are the remains of single-celled organisms like bacteria, with more complicated things like animals and plants only appearing much later. Among the animal fossils, fish appear much earlier than amphibians, birds or mammals. Our closest relatives the apes are only found in the shallowest &ndash youngest &ndash rocks.

"I always think that the most convincing case for evolution is in the fossil record," says Jones. "It's noticeable that one page in every six in the Origin of Species is to do with the fossil record. [Darwin] knew that that was an irrefutable case that evolution had taken place."

How do we really know that one species evolved into another?

By carefully studying fossils, scientists have been able to link many extinct species with ones that survive today, sometimes indicating that one descended from another.

For example, in 2014 researchers described the fossils of a 55-million year old carnivore called Dormaalocyon, which may be a common ancestor of all today's lions, tigers and bears. The shapes of Dormaalocyon's teeth gave it away.

Still, you may not be convinced. Those animals may all have similar teeth, but lions, tigers and Dormaalocyons are still distinct species. How do we really know that one species evolved into another?

The fossil record is only so much help here, because it is incomplete. "If you look at most fossil records, what you actually see is one form that lasts quite a long time and then the next bunch of fossils that you've got is quite different from what you had before," says Jones.

It is also possible to observe the evolution of a new species as it happens

But as we have dug up more and more remains, a wealth of "transitional fossils" has been discovered. These "missing links" are halfway houses between familiar species.

For instance, earlier we said that chickens are ultimately descended from dinosaurs. In 2000 a team led by Xing Xu of the Chinese Academy of Sciences described a small dinosaur called Microraptor, which had feathers similar to modern birds and may have been able to fly.

It is also possible to observe the evolution of a new species as it happens.

In 2009, Peter and Rosemary Grant of Princeton University in New Jersey described how a new species of finch came into being on one of the Galápagos Islands: the same islands visited by Darwin.

This little group of birds had formed a new species

In 1981, a single medium ground finch arrived on an island called Daphne Major. He was unusually large and sang a somewhat different song to the local birds.

He managed to breed, and his offspring inherited his unusual traits. After a few generations, they were reproductively isolated: they looked different from the other birds, and sang different songs, so could only breed among themselves. This little group of birds had formed a new species: they had "speciated".

This new species is only subtly different from its forebears: their beaks are different and they sing an unusual song. But it is possible to watch far more dramatic changes as they happen.

Richard Lenski of Michigan State University is in charge of the world's longest-running evolution experiment.

It's a very direct demonstration of Darwin's idea of adaptation by natural selection

Since 1988, Lenski has been tracking 12 populations of Escherichia coli bacteria in his lab. The bacteria are left to their own devices in storage containers, with nutrients to feed on, and Lenski's team regularly freezes small samples.

The E. coli are no longer the same as they were in 1988. "In all 12 populations, the bacteria have evolved to grow much faster than did their ancestor," says Lenski. They have adapted to the specific mix of chemicals he gives them.

"It's a very direct demonstration of Darwin's idea of adaptation by natural selection. Now, 20-some years into the experiment, the typical lineage grows about 80% faster than did the ancestor."

In 2008, Lenski's team reported that the bacteria had made a huge leap forward. The mixture they live in includes a chemical called citrate, which E. coli cannot digest. But 31,500 generations into the experiment, one of the 12 populations started feeding on citrate. This would be like humans suddenly developing the ability to eat tree bark.

All living things carry genes, in the form of DNA

The citrate was always there, says Lenski, "so all of the populations have [had] the opportunity in a sense to evolve the ability to use this. But only one of the 12 populations has found their way to do this."

At this point, Lenski's habit of regularly freezing samples of the bacteria proved crucial. He was able to go back through older samples, and trace the changes that led to the E. coli eating citrate.

To do this, he had to look under the hood. He used a tool that wasn't available in Darwin's day, but which has revolutionised our understanding of evolution as a whole: genetics.

All living things carry genes, in the form of DNA.

Genes control how an organism grows and develops, and they are passed on from parent to offspring. When a mother chicken lays lots of eggs, and passes that trait onto her offspring, she does so through her genes.

All modern life has descended from a single common ancestor

Over the last century scientists have catalogued the genes from different species. It turns out that all living things store information in their DNA in the same way: they all use the same "genetic code".

What's more, organisms also share many genes. Thousands of genes found in human DNA may also be found in the DNA of other creatures, including plants and even bacteria.

These two facts imply that all modern life has descended from a single common ancestor, the "last universal ancestor", which lived billions of years ago.

By comparing how many genes organisms share, we can figure out how they are related. For instance, humans share more genes with apes like chimps and gorillas than other animals, as much as 96%. That suggests they are our closest relatives.

We have a common ancestor with chimpanzees

"Try to explain that in any other way than the fact that those relationships are based on a sequence of changes through time," says Chris Stringer of the Natural History Museum in London. "We have a common ancestor with chimpanzees, and we and they have diverged since then from that common ancestor."

We can also use genetics to track the detail of evolutionary changes.

"You can compare different types of bacteria and find the genes that they share," says Nancy Moran at the University of Texas at Austin. "Once you recognise these genes&hellip you can look at how they have evolved in different kinds of populations."

When Lenski went back through his E. coli samples, he found that the citrate-eating bacteria had several changes to their DNA that the other bacteria didn't. These changes are called mutations.

Lenski's E. coli show us that evolution can give organisms radically new abilities

Some of them had happened long before the bacteria developed their new ability. "In and of themselves, [these mutations] did not confer the ability to grow on citrate, but set the stage for subsequent mutations that then conferred that ability," says Lenski.

This complex chain of events helps explain why only one population evolved the ability.

It also illustrates an important point about evolution. A particular evolutionary step may seem extremely unlikely, but if there are enough organisms being pushed to take it, one of them probably will &ndash and it only takes one.

Lenski's E. coli show us that evolution can give organisms radically new abilities. But evolution doesn't always make things better. Its effects are often, to our eyes at least, rather random.

The mutations that lead to changes in an organism are very rarely for the better, says Moran. In fact, most mutations have either no impact, or a negative impact, on the way an organism functions.

Animals that live in dark caves often lose their eyes

When bacteria are confined to isolated environments, they sometimes pick up unwelcome genetic mutations that get passed on directly to every generation. Over time, this gradually hampers the species.

"It really shows the process of evolution," says Moran. "It's not all just adaptation and things getting better, there's also this big potential for things to get worse."

What's more, organisms sometimes lose abilities. For instance, animals that live in dark caves often lose their eyes.

This may seem odd. We tend to think of evolution as a process of biological betterment, of species improving and becoming less primitive. But this is not necessarily what happens.

The notion of betterment can be traced back to a scientist named Jean-Baptiste Lamarck, who was pushing the idea that organisms evolve before Darwin was. His contributions were vital.

What did he mean they wanted to improve? How would you test that?

But unlike Darwin, Lamarck thought that organisms got better at living in their environments as a deliberate reaction to those environments, as though they inherently wanted to improve.

Lamarck's theory would say that giraffes have long necks because their ancestors stretched to reach tall trees, and then passed their newly-acquired long necks on to their offspring.

"Darwin wrote about Lamarck privately and said his theory is complete nonsense, it's untestable," says Jones. "What did he mean they wanted to improve? How would you test that?"

Darwin had an alternative theory: natural selection. It offers a completely different explanation for giraffes' long necks.

Imagine an ancestor of modern giraffes, something a bit like a deer or antelope. If there were lots of tall trees where this animal lived, the animals with the longest necks would get more food, and do better than those with shorter necks.

Animals like giraffes are so striking because they appear so perfectly adapted

After a few generations, all the animals would have slightly longer necks than their ancestors did. Again, those with the longest would do best, so over many years, giraffes' necks would gradually get longer, because those with short necks tended not to have offspring.

The mutations underlying this all happened at random, and were just as likely to produce short necks as long ones. But those short-neck mutations didn't tend to last.

Animals like giraffes are so striking because they appear so perfectly adapted. They live in areas where the trees are tall and only have leaves high off the ground, so of course they have long necks to reach them.

"That kind of image is actually what confuses people, I think, because it looks so perfect, it looks designed," says Moran. But if you look closer, it is the result of a long chain of little changes. "You realise, oh, it's not designed, it's actually one odd event that might have spread and led to another odd event."

We now have all the pieces of evidence that, when put together, show that life has evolved.

Human evolution has always been a concept difficult for some to stomach

Descent with modification, which is caused by random mutations in genes, ultimately leads to gradual changes and the formation of new species &ndash much of it driven by natural selection, which weeds out those organisms that are less suited to their environments.

Finally, let's apply all this to ourselves.

Human evolution has always been a concept difficult for some to stomach, but it's impossible to turn a blind eye to it now, says Stringer.

Homo sapiens is believed to have evolved in Africa before spreading all over the world.

People of European and Asian descent carry Neanderthal genes in their DNA

The fossil record shows a gradual change from ape-like animals walking on all fours to bipedal creatures that gradually developed bigger brains.

The first humans to leave Africa interbred with other hominin species, such as the Neanderthals. As a result, people of European and Asian descent carry Neanderthal genes in their DNA, but people of African descent don't.

This all happened thousands of years ago, but the story is not over. We are still evolving.

For instance, in the 1950s a British doctor called Anthony Allison was studying a genetic disorder called sickle-cell anaemia, which is common in some African populations. People with the disorder have misshapen red blood cells, which don't carry oxygen around the body as well as they might.

For those people, it was worth carrying the sickle-cell mutation

Allison discovered that the east African populations were divided into groups of lowland-dwelling people, who were prone to the disease, and people who lived in the highlands, who were not.

It turned out that people carrying the sickle-cell trait got an unexpected benefit. It protected them from malaria, which was only really a threat in the lowlands. For those people, it was worth carrying the sickle-cell mutation, even if their children might be anaemic.

By contrast, people living in highland areas were not at risk from malaria. That meant there was no advantage to carrying the sickle-cell trait, so its otherwise-harmful nature had meant it disappeared.

Of course, there are all sorts of questions about evolution that we still haven't answered.

Their ancestors go back in an unbroken line for over 3 billion years

Stringer offers a simple one: what was the genetic change that allowed humans to walk upright, and why was that mutation so successful? Right now we don't know, but with more fossils and better genetics, we might someday.

What we do know is that evolution is a fact of nature. It is the basis for life on Earth as we know it.

So next time you're out and about, whether it's in your garden or on a farm or just walking down a road, take a look at the animals and plants around you and think about how they all got there.

Each of the organisms you see, whether it's a tiny insect or a great big elephant, is the latest member of an ancient family. Their ancestors go back in an unbroken line for over 3 billion years, to the dawn of life itself. So do yours.


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E.O. Wilson's Theory of Altruism Shakes Up Understanding of Evolution

In 1975 Harvard biologist E. O. Wilson published Sociobiology , perhaps the most powerful refinement of evolutionary theory since On the Origin of Species . Darwin’s theory of natural selection postulated a brutal world in which individuals vied for dominance. Wilson promoted a new perspective: Social behaviors were often genetically programmed into species to help them survive, he said, with altruism— self-destructive behavior performed for the benefit of others—bred into their bones.

In the context of Darwinian selection, such selflessness hardly made sense. If you sacrificed your life for another and extinguished your genes, wouldn’t the engine of evolution simply pass you by? Wilson resolved the paradox by drawing on the theory of kin selection . According to this way of thinking, “altruistic” individuals could emerge victorious because the genes that they share with kin would be passed on. Since the whole clan is included in the genetic victory of a few, the phenomenon of beneficial altruism came to be known as “inclusive fitness.” By the 1990s it had become a core concept of biology, sociology, even pop psychology.

So the scientific world quaked last August when Wilson renounced the theory that he had made famous. He and two Harvard colleagues, Martin Nowak and Corina Tarnita, reported in Nature that the mathematical construct on which inclusive fitness was based crumbles under closer scrutiny. The new work indicates that self-sacrifice to protect a relation’s genes does not drive evolution. In human terms, family is not so important after all altruism emerges to protect social groups whether they are kin or not. When people compete against each other they are selfish, but when group selection becomes important, then the altruism characteristic of human societies kicks in, Wilson says. We may be the only species intelligent enough to strike a balance between individual and group-level selection, but we are far from perfect at it. The conflict between the different levels may produce the great dramas of our species: the alliances, the love affairs, and the wars.

When you published Sociobiology in 1975, you faced enormous resistance, especially to the implication that human nature was genetically based. Now your colleagues are defending one of key tenets in your book—kin selection—while you try to dismantle it. What do you make of the shifting attitudes in your field? Interesting, isn’t it? But I’m not so sure I pivoted that much on kin selection in Sociobiology . If you look at the opening pages, I had a diagram showing how a future science of sociobiology would be built. Kin selection was a nice little part of it in 1975, but Sociobiology went way beyond that. It goes into demography: how groups are formed, how they compete, how communication evolves. Together with ecology and population genetics, it all formed a framework to help explain the origin of social behavior.

Yet a generation of sociobiologists built their research around the idea of kin selection. How did that happen? They were enchanted by kin selection because it appeared to have a basis in mathematics. It seemed solid and it looked good. It was glamorous.

Your new paper states that the mathematical underpinning of kin selection, called the Hamilton inequality, does not work. Why not? When analyzed to the bottom of its assumptions–when we ask under what conditions it could hold—it applies only to a very narrow set of parameters that don’t actually exist on Earth. Inclusive fitness turns out to be a phantom measure that cannot be obtained.

If inclusive fitness is wrong, how do you explain “eusociality”—when individuals reduce their ability to have offspring of their own to raise the offspring of others? It turns out that there’s only one condition that has to be reached in the course of evolution for eusociality to emerge: A mother or father must raise their young within reach of adequate resources at a defensible nest. Getting from the solitary lifestyle to one that includes a defensible nest can be done in one evolutionary step—one gene change. This turns the concept of inclusive fitness on its head, because the gene change and the social behavior came first. Kinship is a consequence of that, not a cause.

How do these ideas play out in the natural world? Let’s take the example of a bird with helpers at the nest. Supporters of inclusive fitness point to a correlation between the amount of help that the young birds give when they stay at home and how closely they are related to the parents and each other. But the young birds are looking after their extended family only until they have families of their own. By analogy, you might stay home and baby-sit for younger siblings after college, but it’s not out of a sense of kinship toward them. It’s because it makes financial sense until you find a job and move out. What these researchers unwittingly do not mention in their studies is that cases of inclusive fitness are quite unusual in an important way. Each of the bird species lives in an area where nest sites and territories are very scarce, very hard for young birds to get.


Teaching About Evolution and the Nature of Science (1998)

Why is it so important to teach evolution? After all, many questions in biology can be answered without mentioning evolution: How do birds fly? How can certain plants grow in the desert? Why do children resemble their parents? Each of these questions has an immediate answer involving aerodynamics, the storage and use of water by plants, or the mechanisms of heredity. Students ask about such things all the time.

The answers to these questions often raise deeper questions that are sometimes asked by students: How did things come to be that way? What is the advantage to birds of flying? How did desert plants come to differ from others? How did an individual organism come to have its particular genetic endowment? Answering questions like these requires a historical context&mdasha framework of understanding that recognizes change through time.

People who study nature closely have always asked these kinds of questions. Over time, two observations have proved to be especially perplexing. The older of these has to do with the diversity of life: Why are there so many different kinds of plants and animals? The more we explore the world, the more impressed we are with the multiplicity of kinds of organisms. In the mid-nineteenth century, when Charles Darwin was writing On the Origin of Species, naturalists recognized several tens of thousands of different plant and animal species. By the middle of the twentieth century, biologists had paid more attention to less conspicuous forms of life, from insects to microorganisms, and the estimate was up to 1 or 2 million. Since then, investigations in tropical rain forests&mdashthe center of much of the world's biological diversity&mdashhave multiplied those estimates at least tenfold. What process has created this extraordinary variety of life?

The second question involves the inverse of life's diversity. How can the similarities among organisms be explained? Humans have always noticed the similarities among closely related species, but it gradually became apparent that even distantly related species share many anatomical and functional characteristics. The bones in a whale's front flippers are arranged in much the same way as the bones in our own arms. As organisms grow from fertilized egg cells into embryos, they pass through many similar developmental stages. Furthermore, as paleontologists studied the fossil record, they discovered countless extinct species that are clearly related in various ways to organisms living today.

This question has emerged with even greater force as modern experimental biology has focused on processes at the cellular and molecular level. From bacteria to yeast to mice to humans, all living things use the same biochemical machinery to carry out the basic processes of life. Many of the proteins that make up cells and catalyze chemical reactions in the body are virtually identical across species. Certain human genes that code for proteins differ little from the corresponding genes in fruit flies,

Investigations of forest ecosystems have helped reveal the incredible diversity of earth's living things.

mice, and primates. All living things use the same biochemical system to pass genetic information from one generation to another.

From a scientific standpoint, there is one compelling answer to questions about life's commonalities. Different kinds of organisms share so many characteristics of structure and function because they are related to one another. But how?

Solving the Puzzle

The concept of biological evolution addresses both of these fundamental questions. It accounts for the relatedness among organisms by explaining that the millions of different species of plants, animals, and microorganisms that live on earth today are related by descent from common ancestors&mdashlike distant cousins. Organisms in nature typically produce more offspring than can survive and reproduce given the constraints of food, space, and other resources in the environment. These offspring often differ from one another in ways that are heritable&mdashthat is, they can pass on the differences genetically to their own offspring. If competing offspring have traits that are advantageous in a given environment, they will survive and pass on those traits. As differences continue to accumulate over generations, populations of organisms diverge from their ancestors.

This straightforward process, which is a natural consequence of biologically reproducing organisms competing for limited resources, is responsible for one of the most magnificent chronicles known to science. Over billions of years, it has led the earliest organisms on earth to diversify into all of the plants, animals, and microorganisms that exist today. Though humans, fish, and bacteria would seem to be so different as to defy comparison, they all share some of the characteristics of their common ancestors.

Evolution also explains the great diversity of modern species. Populations of organisms

Living fish and fossil fish share many similarities, but the fossil fish clearly belongs to a different species that no longer exists. The progression of species found in the fossil record provides powerful evidence for evolution.

with characteristics enabling them to occupy ecological niches not occupied by similar organisms have a greater chance of surviving. Over time&mdashas the next chapter discusses in more detail&mdashspecies have diversified and have occupied more and more ecological niches to take advantage of new resources.

Evolution explains something else as well. During the billions of years that life has been on earth, it has played an increasingly important role in altering the planet's physical environment. For example, the composition of our atmosphere is partly a consequence of living systems. During photosynthesis, which is a product of evolution, green plants absorb carbon dioxide and water, produce organic compounds, and release oxygen. This process has created and continues to maintain an atmosphere rich in oxygen. Living communities also profoundly affect weather and the movement of water among the oceans, atmosphere, and land. Much of the rainfall in the forests of the western Amazon basin consists of water that has already made one or more recent trips through a living plant. In addition, plants and soil microorganisms exert important controls over global temperature by absorbing or emitting ''greenhouse gases" (such as carbon dioxide and methane) that increase the earth's capacity to retain heat.

In short, biological evolution accounts for three of the most fundamental features of the world around us: the similarities among living things, the diversity of life, and many features of the physical world we inhabit. Explanations of these phenomena in terms of evolution draw on results from physics, chemistry, geology, many areas of biology, and other sciences. Thus, evolution is the central organizing principle that biologists use to understand the world. To teach biology without explaining evolution deprives students of a powerful concept that brings great order and coherence to our understanding of life.

The teaching of evolution also has great practical value for students. Directly or indirectly, evolutionary biology has made many contributions to society. Evolution explains why many human pathogens have been developing resistance to formerly effective drugs and suggests ways of confronting this increasingly serious problem (this issue is discussed in greater detail in Chapter 2). Evolutionary biology has also

Living things have altered the earth's oceans, land surfaces, and atmosphere. For example, photosynthetic organisms are responsible for the oxygen that makes up about a fifth of the earth's atmosphere. The rapid accumulation of atmospheric oxygen about 2 billion years ago led to the evolution of more structured eucaryotic cells, which in turn gave rise to multicellular plants and animals.

contributed to many important agricultural advances by explaining the relationships among wild and domesticated plants and animals and their natural enemies. An understanding of evolution has been essential in finding and using natural resources, such as fossil fuels, and it will be indispensable as human societies strive to establish sustainable relationships with the natural environment.

Such examples can be multiplied many times. Evolutionary research is one of the most active fields of biology today, and discoveries with important practical applications occur on a regular basis.

Those who oppose the teaching of evolution in public schools sometimes ask that teachers present "the evidence against evolution." However, there is no debate within the scientific community over whether evolution occurred, and there is no evidence that evolution has not occurred. Some of the details of how evolution occurs are still being investigated. But scientists continue to debate only the particular mechanisms that result in evolution, not the overall accuracy of evolution as the explanation of life's history.

Evolution and the Nature of Science

Teaching about evolution has another important function. Because some people see evolution as conflicting with widely held beliefs, the teaching of evolution offers educators a superb opportunity to illuminate the nature of science and to differentiate science from other forms of human endeavor and understanding.

Chapter 3 describes the nature of science in detail. However, it is important from the outset to understand how the meanings of certain key words in science differ from the way that those words are used in everyday life.

Think, for example, of how people usually use the word "theory." Someone might refer to an idea and then add, "But that's only a theory." Or someone might preface a remark by saying, "My theory is &hellip." In common usage, theory often means "guess" or ''hunch."

In science, the word "theory" means something quite different. It refers to an overarching explanation that has been well substantiated. Science has many other powerful theories besides evolution. Cell theory says that all living things are composed of

cells. The heliocentric theory says that the earth revolves around the sun rather than vice versa. Such concepts are supported by such abundant observational and experimental evidence that they are no longer questioned in science.

Sometimes scientists themselves use the word "theory" loosely and apply it to tentative explanations that lack well-established evidence. But it is important to distinguish these casual uses of the word "theory" with its use to describe concepts such as evolution that are supported by overwhelming evidence. Scientists might wish that they had a word other than "theory" to apply to such enduring explanations of the natural world, but the term is too deeply engrained in science to be discarded.

As with all scientific knowledge, a theory can be refined or even replaced by an alternative theory in light of new and compelling evidence. For example, Chapter 3 describes how the geocentric theory that the sun revolves around the earth was replaced by the heliocentric theory of the earth's rotation on its axis and revolution around the sun. However, ideas are not referred to as "theories" in science unless they are supported by bodies of evidence that make their subsequent abandonment very unlikely. When a theory is supported by as much evidence as evolution, it is held with a very high degree of confidence.

In science, the word "hypothesis" conveys the tentativeness inherent in the common use of the word "theory." A hypothesis is a testable statement about the natural world. Through experiment and observation, hypotheses can be supported or rejected. As the earliest level of understanding, hypotheses can be used to construct more complex inferences and explanations.

Like "theory," the word "fact" has a different meaning in science than it does in common usage. A scientific fact is an observation that has been confirmed over and over. However, observations are gathered by our senses, which can never be trusted entirely. Observations also can change with better technologies or with better ways of looking at data. For example, it was held as a scientific fact for many years that human cells have 24 pairs of chromosomes, until improved techniques of microscopy revealed that they actually have 23. Ironically, facts in science often are more susceptible to change than theories&mdashwhich is one reason why the word "fact" is not much used in science.

Finally, "laws" in science are typically descriptions of how the physical world behaves under certain circumstances. For example, the laws of motion describe how objects move when subjected to certain forces. These laws can be very useful in supporting hypotheses and theories, but like all elements of science they can be altered with new information and observations.

Glossary of Terms Used in Teaching About the Nature of Science

Fact: In science, an observation that has been repeatedly confirmed.

Law: A descriptive generalization about how some aspect of the natural world behaves under stated circumstances.

Hypothesis: A testable statement about the natural world that can be used to build more complex inferences and explanations.

Theory: In science, a well-substantiated explanation of some aspect of the natural world that can incorporate facts, laws, inferences, and tested hypot


Contemporary Views

Throughout the history of psychology, however, this debate has continued to stir up controversy. Eugenics, for example, was a movement heavily influenced by the nativist approach.

Psychologist Francis Galton, a cousin of the naturalist Charles Darwin, coined both the terms nature versus nurture and eugenics and believed that intelligence was the result of genetics. Galton believed that intelligent individuals should be encouraged to marry and have many children, while less intelligent individuals should be discouraged from reproducing.

Today, the majority of experts believe that both nature and nurture influence behavior and development. However, the issue still rages on in many areas such as in the debate on the origins of homosexuality and influences on intelligence. While few people take the extreme nativist or radical empiricist approach, researchers and experts still debate the degree to which biology and environment influence behavior.

Increasingly, people are beginning to realize that asking how much heredity or environment influence a particular trait is not the right approach. The reality is that there is not a simple way to disentangle the multitude of forces that exist.

These influences include genetic factors that interact with one another, environmental factors that interact such as social experiences and overall culture, as well as how both hereditary and environmental influences intermingle. Instead, many researchers today are interested in seeing how genes modulate environmental influences and vice versa.