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INTERNAL CONSTRAINTS: WHAT THE NEW BIOLOGY TELLS US
"One can spend an entire lifetime correcting a flawed paper published
in a reputable journal and still lose the battle if people like the basic idea."
—V. Hamburger, developmental neurobiologist, cited in Rakic, 2008
As we mentioned earlier, some of our good friends, patented experimental
biologists (usually known as ‘wet biologists) who have read
previous versions of this manuscript, slapped us on the wrist because
they think what we are saying is overkill. They told us, ‘no one is
that kind of Darwinian any more. Wed be happy if that were so,
but there is good reason to doubt that it is. And, if it is true, the
news has not been widely disseminated even among wet biologists
(see, for example, Coyne, 2009). This chapter and the next two are
essentially a summary of why those biologists say what they (rightly)
say. Chapter 5 wades into relatively new territory, even for biologists.
News of what we summarize there has, alas, remained even more
elusive so far.
Strict neo-Darwinists are, of course, environmentalists by definition:
the genotype generates candidate phenotypes more or less at
random; the environment filters for traits that are fitness enhancing.
But there are signs of a deep revisionism emerging in current evolutionary
theory: modern biology urges us to conclude (what Darwin
himself had acknowledged) that the effect of ecological variables on
phenotypes is not the whole story about evolution. Indeed it goes
further, urging us to conclude that ecological variables arent even the
most important part of the story about evolution. We will now see, in
summary, how and why contemporary biology has changed classical
neo-Darwinian adaptationism beyond recognition. Many important
discoveries and many explicit quotes by their discoverers bear witness
to this momentous change. Our book as a whole, however, parts
company with many of these distinguished biologists. Paraphrasing
a famous slogan by Karl Marx (an author whose views we do not consider
to be otherwise germane), we can say: biologists have changed
neo-Darwinism in many ways; the point now is to subvert it.
Natural selection is real, of course (when properly construed)
There can be little doubt that shifting equilibria (that is, variations
in the relative frequencies of phenotypic types within and across
populations) happen all the time, on land, in the seas, in lakes, in
rivers and in streams all over this planet. They also happen within
our bodies. Alterations in epithelial (skin) cells, pancreatic cells, lymphocytes
(white blood cells), neurons and synapses occurred in us
even as we wrote these lines and in you even as you read them. Such
shifts are relentless and have been happening on Earth for hundreds
of millions of years. And webs of relations of predation, commensalism
(food-sharing), competition and migration are intermingled with
these shifts and modify, in the long run, our structure and that of our
ecosystems. The distributions of biological and behavioural traits in
populations that we see today are results of these processes, although
certainly not exclusively so, and probably not even chiefly so (assuming
that a reliable measure [a reasonable metric] could be established
for such probabilistic evaluations, a topic to which we will return).
Its common ground that distributions of phenotypic traits in
populations change slightly and relentlessly over time. Having said
this much, however, it must be emphasized that such shifting equilibria
do not explain the distribution of phenotypes; rather, they are
among the phenomena that theories of evolution are supposed to
explain. These days biologists have good reasons to believe that selection
among randomly generated minor variants of phenotypic traits
falls radically short of explaining the appearance of new forms of
life. Assuming that evolution occurs over very, very long periods does
not help if, as we believe, endogenous factors and multilevel genetic
regulations play an essential role in determining the phenotypic
options among which environmental variables can choose. Contrary
to traditional opinion, it needs to be emphasized that natural selection
among traits generated at random cannot by itself be the basic
principle of evolution. Rather there must be strong, often decisive,
endogenous constraints and hosts of regulations on the phenotypic
options that exogenous selection operates on. We think of natural
selection as tuning the piano, not as composing the melodies. Thats
our story, and we think its the story that modern biology tells when
its properly construed. We will stick to it throughout what follows.
We think (and will argue in later chapters) that there are convincing
a priori arguments that show this. For the moment, however,
concede that its often very hard to anticipate the effects of applying
a process of selection to a randomly generated population of
traits. Even slight variations in the initial frequencies, in the rates of
random mutation and in the selection coefficients can lead to drastically
different new equilibria. This chapter summarizes a panorama
of specific mechanisms the discovery of which makes the gradualist/
adaptationist theory of natural selection plainly wrong in at least
some cases, because new phenotypic traits arent generated at random
(as they would be if the mutations that they express are independent)
or because adaptation to the ecology plays only a secondary role in
the fixation of the phenotypes, or for both of these reasons.