PHL323. Some thoughts on the Gene Selection Debate.
Some thoughts on the Unit of Selection
We've been asking: what is the unit of selection? The
answer that most biologists accept is, the unit of selection is
This question can be a little unclear. This is compounded by the way
we tend to talk about the issue. Even Dawkins has a way of talking
about gene selection that is very confusing. He continually uses
teleological discourse to describe what he means to claim are
non-teleological processes. Thus, when he says that a monkey caring
for another monkey's child is a "mis-fire," he indulges in teleological
talk. The claim is that the gene that leads the primate to care for
a non-kin child appears unlikely to be replicated if it leads frequently
to this kind of behavior. A "misfire" thus means, a behavior caused by
gene(s) x that is not behavior of the kind that would lead to the replication
of gene(s) x and might even inhibit the replication of gene(s) x.
Perhaps a good way to think about this question of selection is as a
question of reductive explanation. Imagine the tree of terrestrial life
laid out before you. We agree that evolution explains how the tree came
to exist, and why it has the shape it has. We can now ask the additional
question: is competition between genes alone sufficient to explain how
the tree came to exist, and why it has the shape it has?
In a superficial sense, the answer is obviously no. The environment
always matters, and the environment is not usually just another gene.
But at least the local environment is assumed to exist for any
of the explanations we might cite. Hence, the question is perhaps
better put: given the environmental factors that all our theories of
life will assume, can we explain how the tree of life came to exist
and why it has the shape it has by adding to our explanation also just
competition between genes? The claim by the genocentrists is that
this is sufficient.
Also, obviously, physical constraints (what chemistry can and cannot
do, for example) apply to all the kinds of explanation biology might
provide. It would be trivial to say physics matters -- at least for
some philosophers and biologists, since some philosophers and
biologists assume physics will explain everything. The point is more
like: there are constraints to what the gene explanation can do which
arise from chemical and other physical limitations (e.g., an organism
can only be so strong, it costs such and such energy to move at such
and such a speed, cold inhibits life chemistry, etc.).
Thus, our question for the genocentric explanation is, are the following
sufficient to explain the biological kinds and individuals we see?
Genocentrism says these three are sufficient. Alternative theories
claim that at least in some cases a complete explanation will require
reference to some additional kinds of things (groups, species,
asteroids, etc.). That is, an alternative would be if some trait,
population, or other feature of the tree of life had to be explained
by reference to something other than just the local environment and
the physics and the genes involved -- such as the species, the group,
the clade, and so on.
Note that the struggle between reduction and anti-reductive views
arises all the time. It is a key kind of issue in all of metaphysics.
We always try to explain a phenomenon as simply as we can, but
sometimes we find that we cannot produce an adequate explanation
without adding extra elements to our theories. The genocentrists are
saying we can explain terrestrial life with just gene competition and
a few other things. Others are denying this. We can think of the
genocentrists as taking the conservative, reductive position (everyone
involved in the debate agrees that there is gene selection, so that's
not in dispute; it would thus be most conservative or simple if it
turned out that gene selection and a little bit more was sufficient).
(For these arguments, we should remember that all bets are off when we
consider human beings. Human beings seem to muddle everything up.
Even Dawkins is going to abandon his genocentrism when we get to human
beings, and introduce the idea of the meme. He will not describe the
meme as an exception to genocentrism, but in a way it is, if we
include human culture in biology. But let us set homo sapiens aside
for now, and talk largely about all life but human life.)
Dawkins recognizes, rightly so, two problems: sex and death. Sex
jumbles up the genes. Death terminates a copy of the gene. Both seem to
require some hard thinking if we are to propose how they can be consistent
with genocentrism. We discussed another challenge: cases of eusocial
organisms, which (at least at first glance) appear to suggest that group
selection may be occuring. Finally, we considered a problem which Dawkins
did not discuss: macro-evolutionary trends which do not appear to be well
explained by micro-evolutionary continual progress.
I think it's safe to say that at this point, these debates are still alive,
but mostly the genocentrists are considered victors. The exception is that
it seems the kind of macro-evolutionary differences described by Jablonski
would, if further corroborated, be widely agreed to require some emendation
of simple genocentrism. The result would be that we would want a revised
genocentrism that meant something like the theory that the tree of life will
be explained by:
some special non-local events (like mass extinction events).
One other issue deserves mention, and it will arise several times
again as we talk about applications of evolutionary theory to things
like human behavior. This is the view called sometimes
"adaptationism." Sometimes this is meant as an epithet, but here I
mean the term in the following sense: the view that, because of the
long history of evolution and the many selection pressures put upon
the ancestors of all existing organisms, we can reliably assume that
each inherited structural feature of an organism was selected, and
thus performs some function. A stronger but related adaptationist
claim, often implicit, is that any possible trait that would be
beneficial will ultimately evolve.
Adaptationism is a controversial thesis. For our purposes, as
philosophers worried about the adequacy of conceptions and
explanations, it raises some concerns about whether the kinds of uses
of adaptationism are appropriate. What kind of worry? Well, note
that when Dawkins, to pick one example, considers group-selection
accounts, he immediately responds by saying that these kinds of
accounts are implausible because a mutant will destroy the account.
Thus, the group selectionist says that an altruistic gene in a group
spreads because it helps that group overcome competing groups. The
genocentrist says, this explanation cannot work because a selfish
mutant member (that is, an individual without the altruism trait) of
the group will exploit the altruism of the others, benefit
disproportionately as a result, and soon the whole group will contain
only the offspring of the self mutant. Now, consider how this response
works: it assumes that the selfish mutant is always possible. That is,
it assumes some form of adaptationism.
Contrast this with Dawkins's claims about the penis in mammals without
a penis bone (see in our edition the endnote on page 304ff, which is
an endnote to page 158 of chapter 9). He proposes that this evolved
to signal a healthy heart. Now, that's not in the interest of the
males, so why would that come about? He proposes that the females
learned to contrast the erect and unerect penis of an individual, and
so this creates a selection pressure for males to have a strong
contrast, and this can be done with having a penis without a penis
bone, but rather that must be inflated with blood under pressure.
Now, some animals have retractable penis bones. Why didn't "cheater"
mutants just evolve a retractable penis bone? The implicit answer
seems to be that that's difficult to do. And indeed some kinds of
evolutionary outcomes must be more difficult (less likely, require
more energy, etc.) than others. But you see the problem: without some
testable account of what is difficult to evolve and what is less
difficult to evolve, we find the adaptationist thesis is in danger of
being used when it supports genocentrism, and set aside when it is
inconvenient. When we attack group selection, we trot it out and just
assert that the relevant kind of mutant is possible; when on the other
hand some feature seems inconsistent with genocentrism, we cite
constraints on what's evolutionarily possible. The methodological
problem is: how do we verify when such moves are appropriate, and when
they are cheating?