Is Darwin’s ‘Survival of the Fittest’ theory going Extinct?

READERS in search of literature about Darwin or Darwinism will have no
trouble finding it. Recent milestone anniversaries of Darwin’s birth
and of the publication of On the Origin of Species have prompted a
plethora of material, so authors thinking of adding another volume had
better have a good excuse for it. We have written another book about
Darwinism, and we urge you to take it to heart. Our excuse is in the
title: What Darwin Got Wrong.

By Jerry Fodor and Massimo Piattelli-Palmarini, from the NewScientist

Much of the vast neo-Darwinian literature is distressingly uncritical.
The possibility that anything is seriously amiss with Darwin’s account
of evolution is hardly considered. Such dissent as there is often
relies on theistic premises which Darwinists rightly say have no place
in the evaluation of scientific theories. So onlookers are left with
the impression that there is little or nothing about Darwin’s theory to
which a scientific naturalist could reasonably object. The
methodological scepticism that characterises most areas of scientific
discourse seems strikingly absent when Darwinism is the topic.

Try these descriptions of natural selection, typical of the laudatory
epithets which abound in the literature: “The universal acid”
(philosopher Daniel Dennett in Darwin’s Dangerous Idea, 1995); “a
mechanism of staggering simplicity and beauty… [it] has been called
the greatest idea that anyone ever had… it also happens to be true”
(biologist Jerry Coyne in Why Evolution is True, 2009); “the only
workable theory ever proposed that is capable of explaining life we
have” (biologist and ethologist Richard Dawkins, variously). And as
Dennett continues in Darwin’s Dangerous Idea: “In a single stroke, the
idea of evolution by natural selection unifies the realm of life,
meaning, and purpose with the realm of space and time, cause and
effect, mechanism and physical law.”

Golly! Could Darwinism really be that good?

Darwin’s theory of evolution has two connected parts: connected, but
not inseparable. First, there is an explanation of the taxonomy of
species. It is an ancient observation that if you sort species by
similarities among their phenotypes (a phenotype being a particular
creature’s collection of overt, heritable biological properties) they
form the hierarchy known as a “taxonomic tree”.

This is why most vertebrate species are more similar to one another
than they are to any invertebrate species, most species of mammals are
more similar to one another than they are to any species of reptiles,
and so forth. Why is this? It is quite conceivable that every species
might be equally different from every other. What explains why they
aren’t?

Darwin suggested a genealogical hypothesis: when species are relatively
similar, it’s because they are descended from a relatively recent
common ancestor. In some ways, chimps seem a lot like people. This is
not because God created them to poke fun at us, or vice versa; it is
because humans and chimps are descended from the same relatively recent
primitive ape.

The current consensus is that Darwin was almost certainly right about
this. There are plausible exceptions, notably similarities that arise
from evolutionary convergence, but evidence from a number of
disciplines, including genetics, evolutionary developmental biology and
palaeontology argues decisively for Darwin’s historical account of the
taxonomy of species. We agree that this really was as brilliant an idea
as it is generally said to be.

But that cannot be the whole story, since it is not self-evident why
species that have a recent common ancestor–as opposed, say, to
species that share an ecology–are generally phenotypically similar.
Darwin’s theory of natural selection is intended to answer this
question. Darwinists often say that natural selection provides the
mechanism of evolution by offering an account of the transmission of
phenotypic traits from generation to generation which, if correct,
explains the connection between phenotypic similarity and common
ancestry.

Moreover, it is perfectly general: it applies to any species,
independent of what its phenotype may happen to be. And it is
remarkably simple. In effect, the mechanism of trait transmission it
postulates consists of a random generator of genotypic variants that
produce the corresponding random phenotypic variations, and an
environmental filter that selects among the latter according to their
relative fitness. And that’s all. Remarkable if true.

Compelling evidence

But we don’t think it is true. A variety of different considerations
suggesting that it is not are mounting up. We feel it is high time that
Darwinists take this evidence seriously, or offer some reason why it
should be discounted. Our book about what Darwin got wrong reviews in
detail some of these objections to natural selection and the evidence
for them; this article is a brief summary.

Here’s how natural selection is supposed to work. Each generation
contributes an imperfect copy of its genotype–and thereby of its
phenotype–to its successor. Neo-Darwinism suggests that such
imperfections arise primarily from mutations in the genomes of members
of the species in question.

What matters is that the alterations of phenotypes that the mechanisms
of trait transmission produce are random. Suppose, for example, that a
characteristic coloration is part of the phenotype of a particular
species, and that the modal members of the ith generation of that
species are reddish brown. Suppose, also, that the mechanisms that copy
phenotypes from each generation to the next are “imperfect” in the
sense given above. Then, all else being equal, the coloration of the i
+ 1th generation will form a random distribution around the mean
coloration of the parent generation: most of the offspring will match
their parents more or less, but some will be more red than brown, and
some will be more brown than red.

This assumption explains the random variation of phenotypic traits over
time, but it doesn’t explain why phenotypic traits evolve. So let’s
further assume that, in the environment that the species inhabits, the
members with brownish coloration are more “fit” than the ones with
reddish coloration, all else being equal. It doesn’t much matter
exactly how fitness is defined; for convenience, we’ll follow the
current consensus according to which an individual’s relative fitness
co-varies with the probability that it will contribute its phenotypic
traits to its offspring.

Given a certain amount of conceptual and mathematical tinkering, it
follows that, all else again being equal, the fitness of the species’s
phenotype will generally increase over time, and that the phenotypes of
each generation will resemble the phenotype of its recent ancestors
more than they resemble the phenotypes of its remote ancestors.

That, to a first approximation, is the neo-Darwinian account of how
phenotypes evolve. To be sure, some caveats are required. For example,
even orthodox Darwinists have always recognised that there are plenty
of cases where fitness doesn’t increase over time. So, for example,
fitness may decrease when a population becomes unduly numerous (that’s
density-dependent selection at work), or when a species having once
attained a “fitness plateau” then gets stuck there, or, of course, when
the species becomes extinct.

Such cases do not show that neo-Darwinism is false; they only show that
the “all else being equal” clauses must be taken seriously. Change the
climate enough and the next generation of dinosaurs won’t be more fit
than its parents. Hit enough dinosaurs with meteors, and there won’t be
a next generation. But that does not argue against Darwinian selection,
as this claims only to say what happens when the ecology doesn’t
change, or only changes very gradually, which manifestly does not apply
in the case of the dinosaurs and the meteorite strikes.

So much for the theory, now for the objections. Natural selection is a
radically environmentalist theory. There are, therefore, analogies
between what Darwin said about the process of evolution of phenotypes
and what the psychologist B. F. Skinner said about the learning of what
he called “operant behaviour”–the whole network of events and factors
involved in the behaviour of humans and non-human animals.

Driven from within

These analogies are telling. Skinner’s theory, though once fashionable,
is now widely agreed to be unsustainable, largely because Skinner very
much overestimated the contribution that the structure of a creature’s
environment plays in determining what it learns, and correspondingly
very much underestimated the contribution of the internal or
“endogenous” variables–including, in particular, innate cognitive
structure.

In our book, we argue in some detail that much the same is true of
Darwin’s treatment of evolution: it overestimates the contribution the
environment makes in shaping the phenotype of a species and
correspondingly underestimates the effects of endogenous variables. For
Darwin, the only thing that organisms contribute to determining how
next-generation phenotypes differ from parent-generation phenotypes is
random variation. All the non-random variables come from the
environment.

Suppose, however, that Darwin got this wrong and various internal
factors account for the data. If that is so, there is inevitably less
for environmental filtering to do.

The consensus view among neo-Darwinians continues to be that evolution
is random variation plus structured environmental filtering, but it
seems the consensus may be shifting. In our book we review a large and
varied selection of non-environmental constraints on trait
transmission. They include constraints imposed “from below” by physics
and chemistry, that is, from molecular interactions upwards, through
genes, chromosomes, cells, tissues and organisms. And constraints
imposed “from above” by universal principles of phenotypic form and
self-organisation–that is, through the minimum energy expenditure,
shortest paths, optimal packing and so on, down to the morphology and
structure of organisms.

Over the aeons of evolutionary time, the interaction of these multiple
constraints has produced many viable phenotypes, all compatible with
survival and reproduction. Crucially, however, the evolutionary process
in such cases is not driven by a struggle for survival and/or for
reproduction. Pigs don’t have wings, but that’s not because winged pigs
once lost out to wingless ones. And it’s not because the pigs that
lacked wings were more fertile than the pigs that had them. There never
were any winged pigs because there’s no place on pigs for the wings to
go. This isn’t environmental filtering, it’s just physiological and
developmental mechanics.

So, how many constraints on the evolution of phenotypes are there other
than those that environmental filtering imposes? Nobody knows, but the
picture now emerging is of many, many of them operating in many, many
different ways and at many, many different levels. That’s what the
evolutionary developmental school of biology and the theory that gene
regulatory networks control our underlying development both suggest.
And it strikes us as entirely plausible.

It seems to us to be no coincidence that neo-Darwinian rhetoric in the
literature of experimental biology has cooled detectably in recent
years. In its place, we find evolutionary biologist Leonid Kruglyak
being quoted in Nature in November 2008 (vol 456, p 18) thus: “It’s a
possibility that there’s something [about the contributions of genomic
structure to the evolution of complex phenotypes] we just don’t
fundamentally understand… That it’s so different from what we’re
thinking about that we’re not thinking about it yet.”

And then there is this in March 2009 from molecular biologist Eugene
Koonin, writing in Nucleic Acids Research (vol 37, p 1011):
“Evolutionary-genomic studies show that natural selection is only one
of the forces that shape genome evolution and is not quantitatively
dominant, whereas non-adaptive processes are much more prominent than
previously suspected.” There’s quite a lot of this sort of thing around
these days, and we confidently predict a lot more in the near future.

Darwinists say that evolution is explained by the selection of
phenotypic traits by environmental filters. But the effects of
endogenous structure can wreak havoc with this theory. Consider the
following case: traits t[1] and t[2] are endogenously linked in such a
way that if a creature has one, it has both. Now the core of natural
selection is the claim that phenotypic traits are selected for their
adaptivity, that is, for their effect on fitness. But it is perfectly
possible that one of two linked traits is adaptive but the other isn’t;
having one of them affects fitness but having the other one doesn’t. So
one is selected for and the other “free-rides” on it.

We should stress that every such case (and we argue in our book that
free-riding is ubiquitous) is a counter-example to natural selection.
Free-riding shows that the general claim that phenotypic traits are
selected for their effects on fitness isn’t true. The most that natural
selection can actually claim is that some phenotypic traits are
selected for their effects on fitness; the rest are selected for…
well, some other reason entirely, or perhaps for no reason at all.

It’s a main claim of our book that, when phenotypic traits are
endogenously linked, there is no way that selection can distinguish
among them: selection for one selects the others, regardless of their
effects on fitness. That is a great deal less than the general theory
of the mechanics of evolution that the Darwinists suppose that natural
selection provides. Worse still, there isn’t the slightest reason to
suppose that free-riding exhausts the kinds of exceptions to natural
selection that endogenous structures can produce.

“All right,” you may say, “but why should anybody care?” Nobody
sensible doubts that evolution occurs–we certainly don’t. Isn’t this
a parochial issue for professional biologists, with nothing cosmic
turning on it? Here’s why we think that is not so.

Natural selection has shown insidious imperialistic tendencies. The
offering of post-hoc explanations of phenotypic traits by reference to
their hypothetical effects on fitness in their hypothetical
environments of selection has spread from evolutionary theory to a host
of other traditional disciplines: philosophy, psychology, anthropology,
sociology, and even to aesthetics and theology. Some people really do
seem to think that natural selection is a universal acid, and that
nothing can resist its powers of dissolution.

However, the internal evidence to back this imperialistic selectionism
strikes us as very thin. Its credibility depends largely on the
reflected glamour of natural selection which biology proper is said to
legitimise. Accordingly, if natural selection disappears from biology,
its offshoots in other fields seem likely to disappear as well. This is
an outcome much to be desired since, more often than not, these
offshoots have proved to be not just post hoc but ad hoc, crude,
reductionist, scientistic rather than scientific, shamelessly
self-congratulatory, and so wanting in detail that they are bound to
accommodate the data, however that data may turn out. So it really does
matter whether natural selection is true.

That’s why we wrote our book.

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Jerry Fodor is a philosopher and cognitive scientist at Rutgers
University, New Jersey. Massimo Piattelli-Palmarini is a cognitive
scientist at the University of Arizona, Tucson. This essay draws on
material from their new book, What Darwin Got Wrong, published in the
US by Farrar, Straus, and Giroux, and in the UK by Profile