Evolution FAQ

The theory of evolution is scientifically valid, and is possibly the major unifying theme of today's biology. However, many people still have doubts about its validity, or have misconceptions about what evolution entails. We asked several leading biologists - Harvard's professors of biology (in its many modern guises, including molecular biology, systems biology, and medicine) - to give short responses to the following frequently asked questions.

Click on the question to see the responses. (Being updated regularly - check back often!)

1. What is Darwin's theory of evolution?
Prof. Arkhat Abzhanov

It is best to quote Darwin here: "Probably all organic beings which have ever lived on this earth have descended from some one primordial life form. There is grandeur in this view of life that, whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being evolved." Charles Darwin (The Origin of Species). Charles Darwin explained the source (heritable variation from parents to progeny), the need (competition for limited resources) and the mechanism (natural selection) of evolution.

Prof. Abzhanov is an Assistant Professor in the Department of Organismic and Evolutionary Biology. (Website)

Prof. George Church

In oversimplified form: Cycles of generation of diversity plus selective survival enables not just small changes, but most of the physiological, morphological, and behavioral diversity of life on earth.

Prof. Church is Professor of Genetics at the Harvard Medical School. (website)

Dr. Kevin Foster

The key novelty to Darwin's theory is actually the idea of natural selection more than evolution. A number of scholars before Darwin had suggested that species evolve and change over time; an idea that challenged the orthodoxy of the time that all species had remained unchanged since they were created. Notable evolutionists include Lamarck who is famous for suggesting that evolution happened based upon use and disuse: think a giraffe stretching its neck to reach for leaves and then passing that to its offspring, or a mole going blind because it no longer sees light. Indeed, even Darwin's own grandfather Erasmus Darwin discussed the idea of evolution long before Darwin, albeit in the form of a poem!

So what is natural selection? Darwin observed that - like a breeder artificially selecting the most virulent bull or prettiest pigeon - nature had an intrinsic mechanism of 'selecting' certain types of individuals. In particular, Darwin noted that if a) individuals carry traits that can be passed to their offspring, b) these traits affect the ability of individuals to survive and reproduce and finally, that c) there is a limit in the number of individuals that can exist, as their surely is, then those traits that promote survival and reproduction will increase in frequency over time. Some have since complained at Darwin's use of the word "selection" since obviously there is no real selector at work. Nevertheless, this simple but powerful piece of logic now represents the theoretical basis upon which all biology rests.

A final historical note is that Alfred Russel Wallace independently came up with the idea of natural selection. His realization appears to have occurred quite a few years after Darwin but in the end they published the first papers on it together at the Linnean Society of London in 1858.

Dr. Foster is a Bauer Fellow in the Center for Systems Biology

Prof. James Hanken

Darwin’s theory of evolution relies on naturalistic causes and mechanisms to explain the history of life on Earth. It posits that evolution of life involves descent (from common ancestors) with modification (as adaptation to specialized environments). It also posits that at least some of the variation seen among individuals is heritable, and that in many circumstances these individual differ in their ability to compete for resources, avoid predators, reproduce, etc. The better adapted individuals will leave proportionally more offspring to the next generation, and over time these variants will be “favored.”

Prof. Hanken is Professor of Biology and Curator of Herpetology, Alexander Agassiz Professor of Zoology in and Director of the Museum of Comparative Zoology. (website)

2. How have Darwin's theories been revised and expanded upon?
Prof. Arkhat Abzhanov

Darwin knew nothing about DNA and some of the most profound elaborations of his theory came after breakthroughs in molecular biology and genetics. There were multiple minor revisions, for example in understanding the exact nature of different modes of speciation (evolution of new species) and a better appreciation for the speed of evolutionary change. We also have a far more complete paleontological record that produced numerous transitory (intermediate) forms predicted by the theory of evolution.

Prof. Abzhanov is an Assistant Professor in the Department of Organismic and Evolutionary Biology. (Website)

Prof. George Church

Darwinian theory has been expanded to include Mendelian genetics, then genomics, molecular phylogenetic trees, potential pre-biotic chemistries, cultural/digital evolution and experimental evolution.

Prof. Church is Professor of Genetics at the Harvard Medical School. (website)

Dr. Kevin Foster

Darwin was amazingly prescient on a whole range of topics in modern evolutionary biology ranging from social evolution through to sexual selection. However, what Darwin's writing lacked was a mechanism of inheritance: he didn't know about genes. That had to wait until the twentieth century when Gregor Mendel's work on inheritance in peas - performed at the same time as Darwin's book on natural selection was published - was rediscovered and combined with Darwin's ideas.

Dr. Foster is a Bauer Fellow in the Center for Systems Biology

Prof. James Hanken

Darwin’s theories have been revised and expanded upon in two principal ways. First, empirical evidence for the basic fact of evolution—descent with modification from common ancestors—has continued to accumulate, especially in regards to important transitions among major groups, e.g., evolution of terrestrial life, evolution of flight. Secondly, we now know a lot more about the underlying mechanisms. For example, the basic laws of heredity and genetics were revealed about 40 years after Darwin first published the Origin of Species. Molecular biology, which began in the 1950’s, has contributed importantly in both areas.

Prof. Hanken is Professor of Biology and Curator of Herpetology, Alexander Agassiz Professor of Zoology in and Director of the Museum of Comparative Zoology. (website)

Prof. Peter Godfrey-Smith

It is remarkable how much Darwin was able to work out about evolution despite knowing very little about the mechanics of how living systems work, especially (what we now call) genetics. Since Darwin's time, the single biggest additions to evolutionary theory have come from the integration of Darwin's basic ideas with our newer knowledge of genetics. We have also learned a great deal more about the overall history of life, including the time-span involved.

Prof. Godfrey-Smith is Professor of Philosophy in the Department of Philosophy. (Website)

3. How does natural selection work? Is it the same as 'survival of the fittest'?
Prof. Arkhat Abzhanov

Let's again quote Charles Darwin: "In a world of stable populations where each individual must struggle to survive, those with the "best" characteristics will be more likely to survive, and those desirable traits will be passed to their offspring. These advantageous characteristics are inherited by following generations, becoming dominant among the population through time. This is natural selection." Keep in mind that "best" and "fittest" are relative terms. What makes you "best" today may not help you tomorrow.

Prof. Abzhanov is an Assistant Professor in the Department of Organismic and Evolutionary Biology. (Website)

Prof. George Church

Rather than "fittest" (a superlative), a more realistic view is that individuals showing a range of fitness survive in a variable environment. So an organism somewhat "fit" today might be more fit (or less) in the future for different reasons or might expand or shrink at random (genetic drift).

Prof. Church is Professor of Genetics at the Harvard Medical School. (website)

Prof. James Hanken

If some of the variation among individuals of the same species is heritable, and if there is corresponding variation among those individuals in their tendency to survive and reproduce, then that species will evolve in the direction of the favored individuals. That is evolution by natural selection. We tend to think of differential survival and reproduction as being mediated by the external biotic or abiotic environment (e.g., predators, temperature regime), and so frequently view natural selection as promoting “adaptation” to the environment.

Prof. Hanken is Professor of Biology and Curator of Herpetology, Alexander Agassiz Professor of Zoology in and Director of the Museum of Comparative Zoology. (website)

Prof. Peter Godfrey-Smith

The phrase "survival of the fittest" is not a good summary of how natural selection works. The concept of "fitness" is a constant source of confusion. It is best to give the initial summary of natural selection without even using the concept. Here is the basic set-up Darwin described: (i) a population contains variation between individuals with respect to their structure, behavior, or physiology, (ii) some individuals have features that enable them to survive and reproduce better than others, and (iii) these features are inherited over generations. When these conditions are met, change in the population will usually occur. That is evolution by natural selection.

Prof. Godfrey-Smith is Professor of Philosophy in the Department of Philosophy. (Website)

4. Is eugenics based on evolutionary principles?
Prof. Arkhat Abzhanov

Not at all. In fact, eugenics is largely based on the assumption that Natural Selection no longer works on human species and, thus, its (humankind's) "fitness" needs to be maintained by rather artificial needs (by humans themselves).

Prof. Abzhanov is an Assistant Professor in the Department of Organismic and Evolutionary Biology. (Website)

Prof. George Church

Eugenics has too much pseudoscience baggage to be valued today. The question could be rephrased: Do people try to exercise some control over the genetic (and non-genetic) inheritance of their offspring (e.g. by mate choice, prenatal genetic diagnosis, etc) and does this reflect Darwinian evolution? The answer is yes.

Prof. Church is Professor of Genetics at the Harvard Medical School. (website)

Prof. Gonzalo Giribet

The idea of eugenics may be based on evolutionary principles, but the ideology behind it is certainly flawed. However, we practise 'eugenics' with domestic animals and crops, and people select their couples based on biological features they favor, such as intelligence, or others. Fortunately in general there is no standard criterion or mandated restrictions about who and how to choose for a couple, and therefore evolution continues.

Prof. Giribet is Professor of Organismic and Evolutionary Biology and Curator of Invertebrates in the Museum of Comparative Zoology. (Website)

5. What evidence is there for biological evolution?
Prof. Arkhat Abzhanov

These are some of the main lines of evidence for evolution (past and present): unity of life via common descent (universal genetic code and common mechanisms for encoding and deciphering genetic information in all living forms), transitional forms (from major morphological features such as legs on ancient whales to the more subtle transitions on the molecular level), biogeography (distribution of species that only makes sense considering the history of the landscape), and modern observations of speciation (from microbes to Darwin's finches).

Prof. Abzhanov is an Assistant Professor in the Department of Organismic and Evolutionary Biology. (Website)

Prof. George Church

This is a big topic, but some exciting present/future directions lie in laboratory-scale experiments that can greatly accelerate evolution for practical applications and increased understanding of the power of evolution. These activities include 1) selecting functional molecules from a large collection of random nucleic acids, 2) combinatoric exploration of selected subsets of genomes in rapidly dividing organisms, 3) "biologically inspired engineering" of inorganic or hybrid systems.

Prof. Church is Professor of Genetics at the Harvard Medical School. (website)

Prof. James Hanken

Historically, there have been three great categories of evidence for biological evolution: paleontology (the sequence of ancestors and descendants whose remains we see in the fossil record); comparative anatomy (patterns of anatomical similarity and difference among species); and embryology (the tendency for closely related species to share features of embryonic development more than distantly related species). To this we must add a fourth category, genetic evidence (patterns of similarity and difference among species in their DNA sequences, and the basic fact that all of life utilizes the same basic chemical basis of heredity).

Prof. Hanken is Professor of Biology and Curator of Herpetology, Alexander Agassiz Professor of Zoology in and Director of the Museum of Comparative Zoology. (website)

Prof. Gonzalo Giribet

The world with all its biodiversity and how all that information is contained in the DNA and RNA of those organisms!

Prof. Giribet is Professor of Organismic and Evolutionary Biology and Curator of Invertebrates in the Museum of Comparative Zoology. (Website)

6. Does evolution equal progress? Are humans the pinnacle of evolution?
Prof. Arkhat Abzhanov

Evolution is progressive in a sense that it is a forward moving and often irreversible process. However, it is not progressive in terms of "improvement": organisms simply adapt to their changing environments. All species are pinnacles of their own evolutionary paths.

Prof. Abzhanov is an Assistant Professor in the Department of Organismic and Evolutionary Biology. (Website)

Prof. George Church

Progress is less well defined than evolution, but what if we defined "progress" as steps toward infinite survival ? – This could include getting some life off of our planet before an asteroid hits, plus the deep scientific and humanistic wisdom that might be required to achieve that goal. Pre-human evolution was not obviously on such a track, but as it turned out we may now be closer to that track. So evolution might be compatible with progress in some scenarios, but in others the entire biosphere could vanish.

Prof. Church is Professor of Genetics at the Harvard Medical School. (website)

Prof. Gonzalo Giribet

No, evolution does not equal progress. Organisms evolve by many factors and selection may act upon the organismal traits. What may be selected under certain environmental conditions at a given time, may have not been selected under other conditions. So evolution equates change, opportunity, and adaptation to certain conditions, but those conditions may be bad general conditions (e.g., organisms could adapt to polluted waters). Is this progress? I do not think so.

Humans are definitely not the pinnacle of evolution. Humans, as as species (i.e., Homo sapiens) will go extinct, as any other species will or have done already, and their lineage (descendants of H. sapiens) may end up giving origin to other hominid species or go extinct. If they were the pinnacle of anything, that would imply that evolution has reached an end, but the universe and the organisms that leave in it keep changing.

Prof. Giribet is Professor of Organismic and Evolutionary Biology and Curator of Invertebrates in the Museum of Comparative Zoology. (Website)

Prof. Peter Godfrey-Smith

Evolution has no "pinnacle." It is open-ended, and who knows what it will produce in the future? There are things that humans can do better than any other organism (for example, we are very good at vocal communication). But there are plenty of things that other organisms can do better than us. I admire cuttlefish for changing the color of their skin in less than a second, for example. That is an amazing evolutionary product. Evolutionary theory does not give us a basis for saying that one organism is more "advanced" than another in any absolute sense.

Prof. Godfrey-Smith is Professor of Philosophy in the Department of Philosophy. (Website)

7. Is Intelligent Design (ID) a valid alternative to evolution?
Prof. Arkhat Abzhanov

Intelligent Design is not based on scientific method and, thus, can not be a valid alternative to any scientific theory.

Prof. Abzhanov is an Assistant Professor in the Department of Organismic and Evolutionary Biology. (Website)

Prof. George Church

This question includes a significant set of background issues. Creationists and ID-advocates generally don't reject "microevolution", but just "macroevolution" of new types (e.g. the common ancestry of birds and slugs). Have we ruled out the possibility that aliens have taken an interest in our evolution and nudged it? Or was an ancient "design" sufficient to guide all changes in the history of life (without intervention). On a separate tack, most evolution going forward may involve "design" and not be limited to DNA (e.g. digital-cultural evolution), so ID (defined broadly) could become an increasingly relevant discipline (possibly under a different name).

Prof. Church is Professor of Genetics at the Harvard Medical School. (website)

Prof. Richard Losick

Science is a series of arguments that can be tested and refuted. Religion is based on faith. Evolution is a scientific concept whose predictions are supported by a vast body of empirical evidence. Intelligent Design is a faith-based concept that makes no testable assertions. In Darwin's Black Box, Michael Behe argues that living systems exhibit "irreducible complexity" that must be the result of intelligent design rather than arising from the principles of evolution. But this assertion of irreducible complexity makes no testable predictions and therefore is outside the realm of science.

Many things in the natural world that once seemed perplexing and beyond rational explanation (irreducibly complex) later turned out to be simple to comprehend once the answer was known. Prior to 1953, the problem of how the genetic material is duplicated and passed on from generation to generation seemed outside the realm of explanation by the known laws of science. Indeed, one of the fathers of molecular biology, physicist Max Delbruck, was drawn to tackling this very problem because he believed its understanding would require a new law of physics. Instead, the Watson and Crick model for the structure of DNA immediately suggested a simple and testable model for how the genetic material is duplicated that required no new laws of physics or chemistry and that made testable predictions.

The history of science teaches us that it is wise to keep the following question in mind: What is it that we currently and collectively believe is beyond rational explanation that will later prove to be understandable in a straight-forward manner by science?

Prof. Losick is a Harvard College Professor and Maria Moors Cabot Professor of Biology in the department of Molecular and Cellular Biology. (bio, lab)

Prof. Gonzalo Giribet

Of course not. Evolution is a scientific hypothesis that can be tested (e.g., falsified in a Popperian sense). Intelligent design cannot be tested because any test attempted to falsify it will end up with the same answer, God did it. So there can be believers in ID, but evolution is not a matter of belief!

Prof. Giribet is Professor of Organismic and Evolutionary Biology and Curator of Invertebrates in the Museum of Comparative Zoology. (Website)

Prof. James Hanken

No. It may be a valid alternative in the eyes of some, but it is not a valid scientific alternative. Attempts to represent ID as a scientific theory have failed miserably; they simply have no empirical or theoretical support. Creationist challenges to evolutionary biology are highly flawed; they grossly distort reality. To be sure, there still is a lot about evolution that we (scientists) don’t yet know, but nothing that we do know gives us any reason to abandon Darwin’s theory—as it stands today—and instead embrace ID.

Prof. Hanken is Professor of Biology and Curator of Herpetology, Alexander Agassiz Professor of Zoology in and Director of the Museum of Comparative Zoology. (website)

8. What relevance does evolution have for me?
Prof. Arkhat Abzhanov

Practically everything one sees in the living world today is a product of the evolutionary process. The diversity and complexity of life on this planet can only be understood with knowledge of its history and evolutionary mechanisms that are at work to this day.

Prof. Abzhanov is an Assistant Professor in the Department of Organismic and Evolutionary Biology. (Website)

Prof. George Church

Evolution is increasingly used industrially to make useful products, like biofuels and pharmaceuticals. It is also used to enhance understanding of global health epidemics and various positive and negative aspects of specific alleles in human and agricultural species in various environments.

Prof. Church is Professor of Genetics at the Harvard Medical School. (website)

Prof. Gonzalo Giribet

More than one often can think of. Evolution is the generator of all the diversity we observe, including that which affects us in many ways. Loss of genetic diversity in crops can have fatal effects, due to the lack of evolvability (the capacity to evolve) of such crops. Loss of species or entire ecosystems will have even more dramatic effects. Bacteria evolve quickly, hence the constant battle to develop new antibiotics. Certain viruses can evolve so fast that they skip vaccines. Only by understanding evolution as well as possible can we begin to tackle some of these issues, and many others that we cannot even think of right now.

Prof. Giribet is Professor of Organismic and Evolutionary Biology and Curator of Invertebrates in the Museum of Comparative Zoology. (Website)

Prof. James Hanken

There are many areas in which evolution is relevant to individual humans and human society. For example, evolution posits that humans evolved from earlier species of non-human primates, and ultimately from earlier and even more remote (from us) forms of life, and that humans weren’t “created,” in a bibilical sense. Many of our features of anatomy, physiology, and even behavior thus evolved well before humans did; their presence as human characteristics thus represents the retention of ancestral (prehuman) traits. Modern principles of evolutionary biology also provide important insights into the significance and basis of variation among contemporary human populations.

Prof. Hanken is Professor of Biology and Curator of Herpetology, Alexander Agassiz Professor of Zoology in and Director of the Museum of Comparative Zoology. (website)

Prof. Peter Godfrey-Smith

Suppose you look around you and see a pine tree, a bird, and an ant. If you go far enough back, you all share common ancestors. There is a great-great-great... grandparent of yours who is also the great-great-great... grandparent of the tree, bird, and ant. I am not sure what exactly follows from this, but it seems to me to be a fact with great relevance to how we see our place in the world.

Prof. Godfrey-Smith is Professor of Philosophy in the Department of Philosophy. (Website)

Links to other webpages on evolution can be found in the links page.

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