Clearly at both ends of the spectrum in the debate on evolution, Gould and Dawkins represent the best examples of two great minds expressing two very different views. This article, the first collaborative article between Miguel and preator605, will focus on four topics on evolution on which both scientist's views are quite different and explain their point of view.

Let us put both person into perspective. Stephen Jay Gould, a New-Yorker, born on September 10th, 1941, was an American paleontologist, evolutionary biologist, and historian of science. He spent most of his career teaching at Harvard University and working as a curator of the American Museum of Natural History. He died at the age of 60, on May 20th, 2002.

Richard Dawkins was born in Nairobi in 1941 and his family returned to England in 1949. He was educated at Oxford University and has taught zoology at the universities of California and Oxford. He is the Charles Simonyi Professor of the Public Understanding of Science at Oxford University. His books about evolution and science include: "The Selfish Gene", "The Extended Phenotype", "The Blind Watchmaker", "River Out of Eden", "Climbing Mount Improbable", and most recently, "Unweaving the Rainbow". (Short bio taken from his website, see End-notes).

Here are the words of two of the greatest evolutionary theoretician of our century, on four of the most important philosophical questions of our field. The answers from Stephen Jay Gould were prepared by Miguel and the ones from Dawkins were prepared by preator605.

1. What is the unit of evolution on which selection mainly occurs?

1.1 Stephen Jay Gould: The species.

He is one of the most important defender of the theory of species selection and selection at higher taxonomic levels. Gould says that there exists a macroevolution process that shapes the evolution at and above the species level, and that it is not driven by microevolution, which is the basis of the modern theory.

Natural selection is a theory of ultimate individualism. Darwin's mechanism works through the differential reproductive success of individuals who, by fortuitous possession of features rendering them more successful in changing local environments, leave more surviving offspring. Benefits accrue thereby to species in the same paradoxical and indirect sense that Adam Smith's economic theory of laissez faire may lead to an ordered economy by freeing individuals to struggle for personal profit alone - no accident in overlap, because Darwin partly derived his theory of natural selection as a creative intellectual transfer from Smith's ideas. (Gould 1995, p. 329)

1.2 Richard Dawkins: The genes.

Genes are competing directly with their alleles for survival, since their alleles in the gene pool are rivals for their slot on the chromosomes of future generations. Any gene that behaves in such a way as to increase its own survival chances in the gene pool at the expense of its alleles will, by definition, tautologously, tend to survive. The gene is the basic unit of selfishness. [selfish gene]

The evolutionary importance of the fact that genes control embryonic development is this: it means that genes are at least partly responsible for their own survival in the future, because their survival depends on the efficiency of the bodies in which they live and which they helped to build. [selfish gene]

Individuals are not stable things, they are fleeting. Chromosomes too are shuffled to oblivion, like hands of cards soon after they are dealt. But the cards themselves survive the shuffling. The cards are the genes. The genes are not destroyed by crossing-over, they merely change partners and march on. Of course they march on. That is their business. They are the replicators and we are their survival machines. When we have served our purpose we are cast aside. But genes are denizens of geological time: genes are forever. [selfish gene]

What Dawkins is saying here is that the basic unit of heredity, the gene, is what natural selection and evolution act on primarily. Genes build survival machines, or bodies, in order to survive and be passed on to the next generation. The better the survival machine is built, the better chance the genes have of being passed on. Everything an organism does is usually selfish in nature because it is done to pass the genes on to the next generation. Even altruistic behavior can be described in such ways because the individual organism (survival machine) garners some benefit from cooperating and thus is more likely to pass on its genes. Thus it is the competition between genes and the survival machines they build that are the driving force of evolution.

The messages that DNA molecules contain are all but eternal when seen against the time scale of individual lifetimes. The lifetimes of DNA messages (give or take a few mutations) are measured in units ranging from millions of years to hundreds of millions of years; or, in other words, ranging from 10,000 individual lifetimes to a trillion individual lifetimes. Each individual organism should be seen as a temporary vehicle, in which DNA messages spend a tiny fraction of their geological lifetimes. [blind watchmaker]

2. What is the main mechanism of speciation?

2.1 Stephen Jay Gould: In the late 1970's, he challenged the synthesis model of evolution, and proposed a punctuated equilibrium model, whereby major evolutionary changes took place in limited gene pools after radical climate changes.

In the following quote, Gould is arguing against the belief that human evolution is ending, ushering in a long maturity in which Homo Sapiens persists pretty much unchanged. He is trying to explain to the sceptics why human anatomy has not altered substantially for the past 100 000 years or so. His argument here is a good example of how evolution works in his mind:

Most species are stable during most of their geological duration. Large, successful, well adapted, mobile, geographically widespread species are particularly prone to stability - because evolutionary events are concentrated in episodes of branching speciation within small, isolated populations. (Gould 1995, p. 333)

2.2 Richard Dawkins: The gradual evolution of one species into another, usually by the isolation of a small group in a different environment.

The idea of tiny changes cumulated over many steps is an immensely powerful idea, capable of explaining an enormous range of things that would be otherwise inexplicable.[blind watchmaker]

There would never be a generation in which it made sense to say of an individual that he is homo sapians but his parents are homo ergaster...there is no reason to think that any child was ever a member of a different species from its parents, even though the daisy chain of parents and children stretches back from humans to fish and beyond. [ancestor's tale]

Dawkins and Gould do not really disagree on what is needed for speciation to occur or that it does occur at all. Instead they differ on the rate of speciation and what the evidence shows us. Both of these topics will be addressed next so I will not go in to them here. Suffice it to say that a group of organisms can become isolated in some fashion from the rest of the species. If the selection pressures are significantly different between the two groups, they will begin to diverge and (over thousands if not millions of years) eventually evolve into at least two distinct breeding groups.

3. How do you explain gaps in the fossil record?

3.1 Stephen Jay Gould: The absence of fossil evidence is explained by the very process of evolution, Punctuated Equilibrium, which states that major evolutionary changes took place in limited gene pools after radical climate changes and therefore seems to happen as a sudden event.

The absence of fossil evidence for intermediary stages between major transitions in organic design, indeed our inability, even in our imagination, to construct functional intermediates in many cases, has been a persistent and nagging problem for gradualistic accounts of evolution. (Gould 1980 , p.140)

3.2 Richard Dawkins: Instead of great leaps of evolutionary change, the gaps in the fossil record are a result of the very process of fossil formation. Because fossil formation is rare, we only find good records in certain places for certain times. We thus get an incomplete picture of the entire fossil record because what we have recorded in one area is unlikely to reflect changes in another. Also, the fossil record would not show a smooth continuous change even if we had a fossil of every organism that ever existed.

But since fossilization is such a chancy business, and finding such fossils as there are is scarcely less chancy , it is as though we had a cine film with most of the frames missing. [blind watchmaker]

Thus our picture of the fossil record has "gaps" because we do not have fossils for every organism nor should we expect to find such a complete record. The very act of speciation may be occurring somewhere else on the planet so when the "new" animals return to their old area or appear in the fossil record, it seems as if an evolutionary jump has taken place. But this is not accurate. Organisms do not make large jumps in a small number of generations to produce an entirely new species. Rather, they gradually evolve into a new species in a process that is not always reflected in the fossil record and is not produced under a uniform speed.

The 'gaps', far from being annoying imperfections or awkward embarrassments, turn out to be what we should positively expect, if we take seriously our orthodox neo-Darwinian theory of speciation. ... The point that Eldredge and Gould were making, then, could have been modestly presented as a helpful rescuing of Darwin and his successors from what had seemed to them an awkward difficulty. Indeed that is, at least in part, how it was presented - initially. ... Eldredge and Gould could have made this their main message: Don't worry Darwin, even if the fossil record were perfect you shouldn't expect to see a finely graduated progression if you only dig in one place, for the simple reason that most of the evolutionary change took place somewhere else. ... But no, instead they chose, especially in their later writings in which they were eagerly followed by journalists, to sell their ideas as being radically opposed to Darwin's and opposed to the neo-Darwinian synthesis. [blind watchmaker]

4. How does PE differ from gradualism?

4.1 Stephen Jay Gould: They are two very different things. According to Stephen Jay Gould and Niles Eldredge, Punctuated Equilibrium is what explains the major events of evolution. In the following quote, taken from a paper explaining their belief, and relatively new theory (Punctuated Equilibria was "invented" in 1973), they both, very clearly, express their opinion on this subject:

We believe that punctuational change dominates the history of life: evolution is concentrated in very rapid events of speciation (geologically instantaneous, even if tolerably continuous in ecological time). Most species, during their geological history, either do not change in any appreciable way, or else they fluctuate mildly in morphology, with no apparent direction. Phyletic gradualism is very rare and too slow, in any case, to produce the major events of evolution. Evolutionaty trends are not the product of slow, directional transformation within lineages; they represent the differential success of certain species, within a clade - speciation may be random with respected to the direction of a trend (Wright's rule).(Gould and Eldredge 1977)

However, punctuated equilibria is not necessarily restrictive in scope and does not represent an attempt to exclude gradualism from speciation by establishing a new dogma for evolutionary tempos. The authors explain hoe they see PE

We see it as fundamentally expensive - as a more adequate picture that should extend the range of paleontological activity by valuing types of data previously neglected. We never claimed either that gradualism could not occur in theory, or did not occur in fact. Nature is far too varied and complex for duch absolutes: Captain Corcoran's "hardly ever" is the strongest statement that a natural historian can hope to make.(Gould and Eldredge 1977)

Therefore, Gould and Eldredge would argue that PE and gradualism do differ in theory, but are far from being mutually exclusive theories. The main problem the authors have with gradualism is its status as restrictive dogma.

For it has the unhappy property of excluding a priori the very data that might refute it. Stasis is ignored as "no data", while breaks are treated as imperfect data.(Gould and Eldredge 1977)

This sentence represent the strongest pro for a change in the theory of evolution. Why would these two example of data should be "non-data" ? Punctuated Equilibria represented a breakthrough in the way scientists looked at evolutionary change and the theory behind it.

4.2 Richard Dawkins: It does not. Punctuated equilibrium is simply gradualism under a different name and was not a revolutionary concept in evolutionary thinking.

The fact is that, in the fullest and most serious sense, Eldredge and Gould are really just as gradualist as Darwin or any of his followers. It is just that they would compress all the gradual change into brief bursts, rather than having it go on all the time; and they emphasise that most of the gradual change goes on in geographical areas away from the areas where most fossils are dug up.[blind watchmaker]

So it is not really the gradualism of Darwin that the punctuationists oppose: gradualism means that each generation is only slightly different from the previous generation; you would have to be a saltationist to oppose that, and Eldredge and Gould are not saltationists. Rather, it turns out to be Darwin's alleged belief in the constancy of rates of evolution that they and other punctuationists object to. [blind watchmaker]

What Dawkins is saying is that the idea that evolution does not occur at a constant rate and can speed up or slow down is not a new one. In fact, Darwin himself was not an extreme (phyletic) gradualist.

It isn't true that Darwin believed that evolution proceeded at a constant rate. He certainly didn't believe it in the ludicrously extreme that I satirized [in a parable that since it took the Israelistes 40 years to get to Palestine, they were only doing 24 yards a day]..., and I don't think he really believed it in any important sense.[blind watchmaker]

What PE really says is that a species can be in equilibrium with its environment until a new selection pressure comes about which will then spur evolution on at an increased rate. This is not a new idea. Few, if any, evolutionary scientists believed that evolution occurred at a constant rate over time. The very idea if phyletic gradualism as put forward by Gould was a straw-man argument that did not represent the ideas expressed in the modern synthesis.

... it is all too easy to confuse gradualism (the belief, held by modern punctuationists as well as Darwin, that there are no sudden leaps between one generation and the next) with 'constant evolutionary speedism' (opposed by punctuationists and allegedly, though not actually, held by Darwin). They are not the same thing at all.[blind watchmaker]

The punctuated part of the idea often misleads people into believing that large jumps within a few generations result in changes in organisms or the production of a new species. That is simple not the case. The rate of evolution in speciation and selection pressure changes is only "punctuated" relative to the speed it was before. The process still takes thousands (or millions) of years and each change is gradual from generation to generation. Now this does not mean that a wing will grow 1cm ever generation at a constant rate but the changes in size will not be very different from those directly before and after it. So it is not the case that the gaps we see in the fossil record is a result of large jumps, but rather is the result of the difficulties on fossil formation discussed earlier.

The theory of punctuated equilibrium is a minor gloss on Darwinism, one which Darwin himself might well have approved if the issue had been discussed in his day. As a minor gloss, it does not deserve a particularly large measure of publicity. .. the theory has been sold - oversold by some journalists - as if it were radically opposed to the views of Darwin and his successors. [blind watchmaker]

What needs to be said now, loud and clear, is the truth: that the theory of punctuated equilibrium lies firmly within the neo-Darwinian synthesis. It always did. It will take time to undo the damage wrought by overblown rhetoric, but it will be undone. The theory of punctuated equilibrium will come to be seen in proportion, as an interesting but minor wrinkle on the surface of neo-Darwinian theory. [blind watchmaker]

So for all of the hype and excitement surrounding Gould and the theory of punctuated equilibrium, it really says nothing new and fits perfectly into the Darwinian view of evolution. Unfortunately the rhetoric of Gould and others have distorted the meaning behind PE and has been the result of much confusion. This is evident by the use of Gould in many anti-evolution books and media, which is absurd. Gould was not anti-evolution and actually disliked creationism in all of its forms. But the way PE was put forward has lead to a broad misunderstanding of what the theory is actually saying. The speed of evolution is not constant and can in fact be slowed down and sped up in dramatic fashion (relative to the immense spans of time of course). And despite the protests of Gould, neither Darwin nor those who followed him disagreed with this idea.

References

• Dawkins, R. 1990. The Selfish Gene, Oxford University Press.
• Dawkins, R. 1996. The Blind Watchmaker, W.W. Norton; reissue edition.
• Gould, S.J., and Eldredge, N. 1977. "Punctuated Equilibria: The Tempo and Mode of Evolution Reconsidered", Paleobiology, Vol.3, No.2. pp.115-151.
• Gould, S.J. 1980. "Is a new and general theory of evolution emerging?", Paleobiology Vol.6, No. 1. pp.119-130.
• Gould, S.J. 1995. Dinosaur in a Haystack. New York: Harmony Books.

External Links

• Stephen Jay Gould Unofficial Archive: Simply the best ressource for evolutionary theory papers, books, and articles.
• The World of Richard Dawkins Archive: The best online ressource on the work and where abouts of Richard Dawkins.