Wokół ewolucji

I Rather Think I Am A Darwinian

Simon Blackburn

When I read the late David Stove's essay So
You think you are a Darwinian? in this journal, I supposed that
biologists or philosophers of biology would have been quick to respond.[1]
But the last eighteen months have shown no sign of this happening. Perhaps
people professionally involved with evolutionary theory have better
things to do, and in some circumstances silence is indeed the best reaction.
But not, I think, on this occasion. Darwin himself spoke wearily of
the standard of criticism not uncommonly reached by theologians and
metaphysicians when they write on scientific subjects; by perpetuating
that unfortunate standard we do philosophy a great disservice. Stove's
essay is also reprinted in a collection of his works - a collection
with accolades by no less than David Lewis and Stephen Stich onthe
cover.[2] A book-length expansion of his
views is now published, although in this paper I shall confine myself
to replying to his arguments as they have appeared in this journal.[3]
People who do not know better will think that there must be something
right in his criticisms. People who do know better may think that philosophy
richly deserves its exile to the margins of serious intellectual pursuit.
So I hope a very brief comment by a philosopher may do something to
restore our tattered dignity.

Stove presents a list of ten Darwinian falsities, and tells us that there
are many more. The ten are:

1. The truth is the total prostitution of all animal life, including Man and
all his airs and graces, to the blind purposiveness of these minute
virus-like substances=92, genes. (Richard Dawkins, The Selfish Gene)

2. 'it is, after all to a mother's advantage that her child should be adopted
by another woman. (ibid.)

3. All communication is manipulation of signal-receiver by signal-sender (ibid.)

4. Homosexuality in social animals is a form of sibling-altruism: that is, your homosexuality
is a way of helping your brothers and sisters to raise more children.
(Robert Trivers, Social Evolution)

5. In all social mammals, the altruism (or apparent altruism) of siblings
towards one another is about as strong and common as the altruism (or
apparent altruism) of parents towards their offspring.
(W. D.Hamilton, The Journal of Theoretical Biology, 1964)

6. no one is prepared to sacrifice his life for any single person, but everyone
will sacrifice it for more than two brothers (or offspring), or
four half-brothers, or eight first-cousins. (ibid. p. 269)

7. Every organism has as many descendants as it can.

8. In every species child-mortality - that is, the proportion of live births
which die before reproductive age - is extremely high.

9. The more privileged people are the more prolific: if one class in a society
is less exposed than another to the misery due to food-shortage, disease,
and war, then the members of the more fortunate class will have (on
the average) more children than the members of the other class.

10. If variations which are useful to their possessors in the struggle for
life do occur, can we doubt (remembering that many more individuals
are born than can possibly survive), that individuals having any advantage,
however slight, over others, would have the best chance of surviving
and of procreating their kind? On the other hand, we may feel sure that
any variation in the least degree injurious would be rigidly destroyed.
(Charles Darwin)

These ten are billed as central, indispensable and characteristic theses of
Darwinism. However, Stove also notices that some of them are only held
by some evolutionary biologists. These he calls ultras, or in other
words those who have been most enthusiastic in applying Darwinian explanations
to a whole variety of behavioural or other features of people and animals.
But although he urges that it is fair to attack a doctrine or approach
by attacking its ultras, this is surely false. For wherea's Darwinism
claims that some features of living things are adaptations, in a sense
we define below, the ultras either think that all of them are, or
at least that certain favourite (alleged) features of people or animals
are. This is not so much an extreme version of Darwinism, as a recipe
for misapplication of it. The ultras are also apt to deliver glib interpretations
of the significance of Darwinism, and this point becomes important when
we return to the first three falsities that Stove presents, all taken
from the writings of the ultra Richard Dawkins. But rather than go
through his ten Darwinian falsities, in his order, I shall start with
the worst example, which also serves to introduce the basics.

The sixth of the parade is supposed to come from W. D. Hamilton, whose paper The
Genetical Evolution of Social Behaviour has been the fountainhead of
much modern evolutionary theory.[4] Here
again is the quotation Stove uses, in the words he gives:
no one is prepared to sacrifice his life for any single person, but everyone
will sacrifice it for more than two brothers [or offspring], or
four half-brothers, or eight first-cousins. (p. 269)

Stove scrupulously explains that the italicization is his own, and so is the
insert in square brackets. But they are scarcely necessary to justify
his own scathing denunciation of Hamilton's view. It is one of the characteristic
Darwinian propositions, Stove tells us, which is obviously false: either
a direct falsity about our species or, where the proposition is a general
one, obviously false in the case of our species, at least. The publisher's
advertisement for Stove's book also claims that Stove has falsified
the prediction that an animal will sacrifice itself for three siblings.
And the unwary reader might well think Stove has a point, for the proposition
is obviously false about our species, so if Hamilton and Darwinians
believe it, they must be badly astray.

But here is the actual quotation from Hamilton:

To express the matter more vividly, in the world of our model organisms, whose
behaviour is determined strictly by genotype, we expect to find that
no one is prepared to sacrifice his life for any single person, but
that everyone will sacrifice it when he can thereby save more than two
brothers, or four half-brothers, or eight first-cousins (p. 16)

By missing out the first twenty-five words, Stove presents a mathematical truth
about Hamilton's model as a contingent falsehood about human
beings.

If Stove knew what he had done, then I think he can only be defended in the words
Sir Peter Medawar used of Teilhard de Chardin in his famous review in
Mind, 1950: its author can be excused of dishonesty only on
the grounds that before deceiving others he has taken great pains to
deceive himself. But if on the other hand he did not see how the omission
matters then Stove is in effect committing one of the very fallacies
that critics claim lie at the heart of vulgar or pop sociobiology,
which is that of inferring actual propensities to behaviour and their
explanations, from genetic models (other fallacies imputed include that
of inferring the existence of a gene =91for=92 any aspect of the phenotype,
just because it exists, and that of inferring the identity of kinds
of behaviour and of evolutionary history, from superficial analogies
across species).

Why does the omission matter so much? Hamilton's paper was centrally acontribution
to population genetics. It was the first formal presentation of the
concept of inclusive fitness: roughly, the extent to which the genetic
material of an organism is represented in future generations. Hamilton
saw that this measure will sometimes increase if a gene codes
for self-sacrificial behaviour. In particular, sacrifices of the type
described, in a population, such as we are, whose members get half their
genetic material from each parent, will actually lead to more of an
individual's genetic material being represented in the next generation
than a non-sacrificial alternative. So, under stable evolutionary conditions,
if there is a variant of a gene (an allele) that codes for such behaviour,
then we would expect animals in which it is present to become predominant
in a population, compared with those with an allele that does not code
for such behaviour. Hamilton went on to apply the model to solve a famous
problem for Darwinian theory: how it can be that in species of hymenoptera
(ants, bees and wasps), sterile workers exist? Why would evolutionary
pressures not have weeded them out? The answer is that sterility could
have evolved under pressure of selection because, given the particular
way genetic material flows through the population, sterility of the
worker can actually increase its genetic representation in future generations:
the sterile worker farms its mother to produce more sisters, to whom
it is more closely related than it would be to its own offspring. So
from the standpoint of inclusive fitness sterility can beadaptive
and it would not be weeded out by evolution. This is a possibility theorem,
similar, for example, to Haldane's earlier answer to the question of
how the gene for sickle cell anaemia, which is almost always lethal,
could persist in human populations. The answer is that although 80%
of people with sickle cell anaemia die before reproducing, the condition
requires the homozygote (SS), the person having received the S gene
from each parent. However, people with the heterozygote (AS) have other
advantages over those who are AA, notably resistance to malaria. It
is as if there is an urn in which a proportion of balls are S, and a
proportion A. Drawings are made two at a time: SS means none go back,
AA means one of the two quite fairly often goes back, but AS or SA means
that one of the two much more often goes back, and that explains why
S persists in the population in the urn. In fact, the S gene is more
prominent in precisely those populations that are more at risk from
malaria.

Now return to self-sacrifice. Nothing in the theory so far predicts that
we, or any other species should behave self-sacrificially in just the
way Haldane and Hamilton described. Why not? Obviously, one reason alone
suffices: the naturalized epistemology is too demanding. That is, it
is obviously extremely hard to recognize the degrees of relatedness
that Hamilton describes, and to adjust any behaviour efficiently to
reflect them accurately (especially remembering the smaller fractions
involved as degrees of relatedness decrease). A likely economical solution
might be an approximation or kludge: sacrifice yourself more readily
for animals that look like your parents or that smell familiar, for
example. Or even: don=92t sacrifice yourself at all under any circumstances.
But furthermore, we don=92t know the costs that would attach to having
behaviour determined by any more accurate device. In some circumstances,
obviously, there would be costs in terms of interference with other
interesting and potentially adaptive mechanisms such as that ofreciprocal
altruism regardless of kin.

But quite apart from this, nothing in Darwinian theory allows you to say that
because some pattern of behaviour would increase the amount of some
type of genetic material in future generations, therefore it will exist.
It does not as it were allow you to say that whatever is right, is.
Nor does it allow you to say that because some trait exists, therefore
it is an adaptation, so that whatever is, is right. Darwin himself was
not a Panglossian: he thought that natural selection is 'insensibly
working, whenever and wherever opportunity offers, at the improvement
of each organic being in relation to its organic and inorganic conditions
of life. But he did not think that opportunity is always offered (in
fact, he specifically discusses circumstances favourable or unfavourable
to the operation of natural selection, in chapter 4 of the Origin).
He also thought that natural selection is but one agent of change,
and one factor responsible for the features of species and their members
at any time.

Why does opportunity not always offer? Genes flow through populations through
time, their numbers in any generation varying with many factors, but
centrally with the reproductive success of organisms that possess them.
This means is that if the difference between the presence of
one allele at a locus and the presence of another allele, causes a difference
in the properties of the organism carrying the gene, and if that
difference causes superior reproductive success of the organism,
then the frequency of the occurrence of the one allele will rise compared
to that of the other. If this is what explains the presence of the phenotypical
difference, then the property is called an adaptation. This is just
definition and mathematics. The empirical and testable question whether
a particular trait is in fact an adaptation. So the first reason why
opportunity does not always offer is that it is history and chance that
determine whether one allele and another exist, and get into the competitive
situation in which natural selection can operate in the first place.
All this is standard theory. Even the ultra Dawkins, for instance,
offers a list of six constraints on perfection, and discusses still
others. The six are: time lags (animals are often out of date); the
biological patchwork apt to be generated by historical constraints,
or in other words the fact that evolution has to work by degrees on
what is already present; the available genetic variation that exists
for evolutionary pressure to work upon; constraints of costs and materials,
imperfections at one level arising because of adaptations at another;
and finally the existence of malevolence in the environment: perfection
in the python is death for the monkey.[5] Interestingly,
Darwin was well aware of the general nature of these constraints, and
himself suggested the principle of =91functional change in structural
continuity to explain the evolution of incipient forms of structures
that only gain their present use later.

Hamilton's result certainly led to the search for kin-related sacrificial and altruistic
behaviour in nature. It also led to various incautious claims that the
phenotypical trait, here a propensity to adjust behaviour to degrees
of relationship, is found in various human contexts, although the anthropological
consensus is that this is not so (typically social kinship matters to
us more than blood ties, although of course they may coincide). It led
to the search for other traits that might, if they are the expression
of a genetic variation, be likely to stabilize or increase in apopulation
not because of direct reproductive success, but only through factoring
in Hamilton's indirect effects, or inclusive fitness: patterns of
fighting, warning, mating, caring, adoption, infanticide, and so on.

Where does this leave Stove? He certainly finds a familiar target in his first
quotation from Richard Dawkins, for nothing in evolutionary biology
supports the image of ourselves as blind, or unable to pursue our own
purposes, nor do they justify the rhetoric of us as prostituted to other,
hidden purposes, possessed by virus-like substances within us. Stove
is perfectly within his rights to join many commentators in finding
Dawkins's language completely inappropriate. Of course, Dawkins knows
and often says that genes have no brains, and hence no purposes and
no self-interest. His problem is that he wants to say this, butat the
same time to promote an interpretation of the biological facts that
is actually inconsistent with it (but formed the core of his populist
appeal). Thus he believes that our only hope in moral and political
affairs to 'defy the selfish genes of our birth and rebel against
the tyranny of the selfish replicators; had Stove confined himself
to pointing out that nothing in the literal science gives any license
to us to think that we do, or could do, or need to do, any suchthing,
then he might have performed a useful service.[6] What
he should not do is read the unhappy rhetoric back into the doctrines
of evolutionary biology. Dawkins's peculiar vision of us as mere vehicles
for purposive genes is of his own making. It is not a tenet of Darwinism.
But Stove is not within his rights to ignore Dawkins's technical use
of terminology, as Dawkins pointed out in his rebuke to Mary Midgley
in this journal a long time ago, and it is this that is at workin the
second and third thesis.[7]

Hamilton's result led to work, such as that of R. Trivers that Stove goes on to
cite, suggesting the we do find direct expression of inclusive fitness
in patterns of behaviour.[8] The idea is that there
are patterns of behaviour that can be interpreted as illustrating an
unconscious calculus of genetic flow. Trivers speculates that the rate
of homosexuality in populations is one such. Now although Trivers's
work is relatively unguarded it is not to be criticized as expressing
outright psychological falsity. Trivers does not suppose, as Stove implies
(p. 269) that homosexuals are really saying to themselves: let me
promote the reproductive success of my relations. How can I do that
best? I know, I shall opt out of the reproductive race, by coupling
only with others of my own sex.' Sure enough, if this were homosexual
psychology, then presumably gays would spend less time cruising and
more time nurturing siblings, nieces and nephews (and in fact, could
perhaps do better for their genes by just confining themselves to these
laudable activities, and giving up sex altogether). But one of the points
of Trivers's work is to show that a pattern of behaviour can exist without
an organism planning, or even having the capacity to plan, in terms
of it (in fact, the relevant example in his book Social Evolution
is lesbianism amongst gulls).[9] All the homosexuals
are doing is finding members of the same sex attractive. But the theorist
asks: why they are doing this? And how is it possible that a gene for
doing it (if it is an adaptation) should survive, when it is
obviously harmful to direct reproductive success? The answer might,
in principle be given by the Hamiltonian calculation, just likethe
sterility of worker bees or ants. But it might not be: the explanation
is speculative, and faces all the obstacles I have mentioned, and perhaps
more.

A theory such as this is speculative because we have to know the heritability
and the plasticity of human patterns of behaviour before even beginning
to theorize about which features of it are adaptations, in the sense
given above. To take the classic example: if we lived only in an English
speaking environment, and observed the remarkable rapidity with which
infants learn English, we might conclude that there is a gene for
speaking English. We would clearly have been misled; at best there might
be a gene for learning whichever language is spoken by those around
us. Perhaps the threat of genetic determinism is less troublesome
once we realize that in many respects we may only be determined to be
flexible. There are certainly genetic, heritable, instructions for growing
proteins, and hence for growing the general-purpose cognitive and emotional
engine called the brain. Equally certainly the brain imposes some limits:
limits on what we can see or hear, or the size of our long or short
term memories, for example, just as gravity puts limits on the size
we can grow, or the distance we can fly. But more interesting behaviour
is a different matter. Psychologically and culturally the empirical
evidence shows massive flexibility within whatever limits there are,
just as it shows it linguistically. A priori then, homosexuality
in humans is at least as likely to be a consequence of various social
and cultural factors as any kind of adaptation.[10]

This kind of defence may seem too good to be true, and it may be appropriate here
to make one remark about the question of whether Darwinism is an empirical,
testable scientific theory, or whether it deflates into the tautology
that survivors survive. The correct response is that these are not the
only alternatives. Darwinism is better seen as a framework within which
the right questions can be asked. It does not itself tell us which phenotypical
properties are adaptations. But it does imply that some are, and the
empirical work comes in discovering which ones these are. It is applying
the genetic model in any particular way that leads to falsifiable empirical
science, and there are many classic studies showing how it can be done.[11]

Stove's main further point (supposed to refute all but the final one of the
ten falsities) is that human beings obviously do not reproduce as prolifically
as they can. This is certainly true, and the anthropological evidence
is that cultural norms show great flexibility and variation in what
counts as an appropriate pattern of childbearing. So, says Stove,
the human being falsifies a central plank of Darwin's theory, which
is that every organism has as many descendants as it can. Stove says
roundly: there can clearly be no question of Darwinism making an exception
of man, without openly contradicting itself (p. 271).

Unfortunately it is simply untrue that Darwinism implies that every organism has as
many descendants as it can, in the sense Stove intends, in which it
means bears or begets as many children as is biologically possible for
it to do (Stove must mean this, or the subsequent calculations of mortality
rates become irrelevant). A kind of organism that did breed to its biological
limit could easily be selected against: most obviously if all its many
offspring promptly starved, where fewer would have survived. This is
why Stove's gloss is not at all equivalent to the quotation from Darwin
that he actually gives, which talks of the striving (tendency would
have been better) to maximize numbers, something which can some times
best be done by restraint in child-bearing.

To understand this situation let us suppose a constant environment in which the number
of human beings cannot grow significantly beyond its present level.
Suppose the population is one of Trimmers, who find it less costly,
more healthy, to restrain their rate of reproduction to roughly two
children per couple, and the status quo is thereby maintained. Suppose
the population now is invaded by a number of Breeders, who devote a
great deal of energy to breeding up to their biological limit of ten
or fifteen children per female. Suppose that a propensity to breed or
to trim is controlled by a single gene. Would we expect the Breeders
to displace the Trimmers? Not at all. We know that in the end, the actual
number in the population remains the same: this is Malthus's grim truth.
So the question is going to be: who is dying? The environment is one
in which two people can be replaced by two people. Breeders are trying
to rear ten or fifteen. Their children are less likely to get fed properly,
are therefore weaker, more prone to disease, and are less able to survive.
Perhaps the parental investment in breeding leads to less investment
in upbringing, so that breeders are not intelligent or strong, and therefore
fail to be sexually selected by the healthiest partners. Perhaps Trimmers
find the reversion to Malthusian controls on population sufficiently
abhorrent to mount other strategies against the Breeders, and so on.
In fact, in biological theory, producing a small number of intensively
cared-for offspring leads to one kind of selection (K-selection); it
is distinguished at least by degree, from producing the largestpossible
number of offspring (r-selection). Birds produce few eggs, and care
for them intensively; fish produce huge numbers of eggs, and don't care
for them at all. We are like birds, but whereas they have presumably
no control over the mechanisms that regulate the size of their clutch,
we do.

Again Stove might more reasonably have applied the fact that many human beings
don't care to reproduce to Dawkins rather than Darwin. That is, a good
way of ridding oneself of his image of us as robots under the control
of our purposive genes is to reflect that the goal of reproducing at
all, let alone reproducing prolifically, is one that many people simply
do not have. Nor need there be any huge psychological cost, as if such
people were constantly fighting a strong innate urge to reproduce, forced
on them by the swarming armies of purposive genes inside them. But when
thinking about Darwin himself, we must remember that, quite apart from
its description in the Origin of Species (e.g. in chapter 4),
parts two and three of The Descent of Man, that is, two thirds
of the entire book (and it is not short), concern sexual selection
in animals and human beings. Darwin considered sexual selection
(the differential preference of members of one sex for members of the
other) as a major agent of evolutionary change through time, comparable
to human breeding of domesticated animals. A bird, for instance, refrains
from mating with another bird who is not preferred; Darwin describes
in chapter 14, and returns later to, the vivid case of several peahens
who, when debarred from an admired male, remained widows during a whole
season rather than pair with another bird (chapter 21). But by exercising
sexual selection an animal refrains from the indiscriminate urge
to reproduce whenever biologically possible. So Stove is in the extraordinary
position of holding that Darwin's most discussed agent of evolutionary
change is in fact inconsistent with a central, indispensable tenet of
the theory.

Because he misinterprets Darwin, Stove's calculations of infant mortality rates
in a stable population in which people do reproduce as often as they
can, are quite beside the point (pp. 271-272). Of course all human societies
take steps to control their fertility, by late marriages, long periods
of suckling, restraints on permissible periods of intercourse, and so
on, just as in birds there are mechanisms that regulate the size of
clutches of eggs. There is no theorem of Darwinian biology that if
a variation appears that has larger clutches it will oust the others:
it all depends on what happens next.

As for Stove's last thrust, in which he finds Darwinism inconsistent with the
existence of injurious attributes in animals, it simply depends on taking
a rhetorical passage of Darwin's for a non-negotiable literaltenet
of the science (p. 275). Darwin knew that we get diseases, just as he
knew that we have parasites, and eventually die. Injurious traits such
as alcoholism and aneurism are not inevitably weeded out, any more than
things which are more clearly under genetic control, such as sterility
or susceptibility to malaria are weeded out, and, ironically, it is
work such as Hamilton's or Haldane's that explains why. The single example
above, of the persistence of a gene for the horrible disease of sickle
cell anaemia should be enough to show why evolutionary biology is committed
to no such optimism. How could it possibly be? As we have already said,
typically a success in one organism is a difficulty for another.

To anticipate misunderstandings, I should repeat that none of this is any kind of
defence of any of the interpretations, or misinterpretations of Darwinian
theory that go under the banners of sociobiology, or evolutionary psychology.
On the contrary, the point about the evolution of a flexible, multi-purpose
brain is precisely intended to unsettle any crude inference from human
phenotype (as discovered, for instance, in the tendencies of some human
population at some time) back to genetic determination, or from genetic
model to actual behaviour. The sociobiologists or ultras may sometimes
commit these fallacies (perhaps the second underlies falsity number
five, which I have not attempted to defend). But we simply share it
with them if we fail to distinguish their misinterpretations of Darwin's
legacy from the legacy itself. In his paper Stove chose not to attack
the perversions of Darwinian theory, but the theory itself. I believe
philosophers need to understand that his weapons were hopelessly ill-adapted
to doing this.[12]

University of North Carolina at Chapel Hill

References
1 D. C. Stove, 'So You Think You are a Darwinian? Philosophy 69, 1994, 267=97277. This is the not the first of Stove's appearances in this journal on the subject: see also A New Religion Philosophy 67, 1992, 233-240.
2 Cricket versus Republicanism (Sydney: Quakers Hill Press, 1995).
3 Darwinian Fairytales (Aldershot: Avebury Books, 1996).
4 W. D. Hamilton, 'The Genetical Evolution of Social Behaviour, The Journal of Theoretical Biology VII ,1964, 1-52.
5 R. Dawkins, The Extended Phenotype, (Oxford University Press 1982), ch 3.
6 R. Dawkins The Selfish Gene (Oxford University Press, 1976). The quotations are from pp. 200-201 of the 1989 edition.
See also p. 332. That Dawkins is in a muddle is evident from the assertion that we, that is our brains, are separate and independent enough from our genes to rebel against them: a remarkable feat, one would have thought. We don't rebel against our brains by using them. Of course
we can think up a sense in which it might be true: we 'rebel against our genetically coded height, for example, every time we climb a ladder.
But in this sense it is not true that we alone on earth rebel against our genes. A bear sheltering in a cave is rebelling against its genetically
coded tendency to freeze in bad weather, in just the same sense. Like many others, Dawkins was trying, but failing, to derive some sweeping
human or philosophical interest from the biology and of course it was the belief that he had done that which gave the book, interesting as
it is in its literal science, its wider reputation. This is also why there is something a little disingenuous in simply sheltering behind
the claim that words like 'selfish or advantage, or purpose or 'manipulate are being used in a technical sense. If I write and profit
from a book on popular biology which I call, say, The Nazi Within, it is a little cheeky of me to say that I was simply using the term
Nazi in a technical sense in which it means bit of chemical that replicates itself over time. This is, I think, the real point buried
in Midgley's paper (p. 448) that Dawkins failed to answer.
7 R. Dawkins In Defence of Selfish Genes, Philosophy 56, 1981, 556-573; M. Midgley, Gene Juggling, Philosophy 54, 1979,
439-458. The second and third of Stove's list of Darwinian falsehoods depend upon misreading technical uses of terms 'advantage
and 'manipulation as they are used in Dawkins's writings. But see also the previous note.
8 R. L. Trivers, The Evolution of Reciprocal Altruism. Quarterly Review of Biology, 46, 35-37.
9 R. L. Trivers, Social Evolution (California:Benjamin/Cummings, 1985) , 198-200.
10 The superficiality of the genetic story is scathingly criticized in Not in Our Genes, Steven Rose, Leon Kamin, and
R. Lewontin, (Harmondsworth: Penguin Books, 1984), 260-261.
11 H. Kettlewell, The Evolution of Melanism (Oxford University Press, 1973) is one of the most revered. One wonders what
Stove's explanation of the relative frequency of black and speckled moths in town and country would be.
12 I would like to thank James Maclaurin and David Braddon-Mitchell for helpful conversation and biological information.
 

Webmaster: Dr Jeremy Stangroom webmaster@royalinstitutephilosophy.org
 


POWRÓT