Re: What Is Evolution?

From: Stevan Harnad (
Date: Mon Oct 06 1997 - 21:14:01 BST

> From: donna crumley <>
> Steve posed the question: What is evolution?
> One way it was described was: passing on 'recipes' for success. These
> "recipes' are not passed on in an abrupt obvious way, rather through a
> very subtle slow moving process.

I'm not sure what you mean by "abrupt and obvious"! They are passed
generation to generation, whether by cloning or by sexual reproduction.
Perhaps you were thinking about the process by which the code in the DNA
is used to make proteins, which is indeed a gradual biochemical

> It seems that the species which are
> most likely to survive are those which pass on its strongest traits to
> the next generation.

Species do not survive per se. It is individuals who live or die. The
point is that the programmes in our genes build us, the "survival
machines," and based on our success in surviving and reproducing, our
selfish genes succeed too. And all that is meant by success is
successfully getting making it into the next generation (or cell

> It is for this reason that sexual reproduction
> (meiosis) is the most successful way of creation.

Meiosis is not sexual reproduction. It is a form of cell-division that
play a critical role in sexual reproduction: Mitosis is a cell division
in which one cell splits into to exact copies of itself. The DNA
(genetic material) in all cells that derive from one another by mitosis
is identical. [The genetic material -- not necessarily the call, because
the genetic material may be programming the cell to make proteins that
the cell from which it was cloned did not make: this is how DNA can
oversee the entire developmental process from fertilised egg to adult
organism all through cloning: every cell has the same genetic material,
but its cell "vehicle" is influenced by space (some DNA programmes
produce different outcomes when they are crowded or when they are not);
some produce different outcomes after a certain period of time has
elapsed; some produce different outcomes when they are in a different
chemical environment).

So that is mitosis, and that is what most cell division and growth in
most species is. The genetic material is arranged in a double helix,
with paired components called chromosomes. In sexually reproducing
species, there is another, special kind of cell division, one that only
takes place in the gonads that produce egg and sperm. This form of
cell-division, meiosis, is called "reduction" division, because the two
cells that result have exactly HALF the genetic material of the
original cell. One strand of the double helix goes to one of them, the
other to the other. Then in reproduction, one of these half-cells, the
sperm, combines with another of these half-cells, the egg, and together
they form an embryo that can grow into the full organism (by ordinary
mitosis) guided by the genetic material, which has been "reshuffled"
by this process. The variability this gentle recombination gives
sexually reproducing organisms more chances in the survival lottery, and
makes it possible for evolution to occur rapidly (from generation to
generation) rather than waiting for cosmic rays or mitosis errors to
provide the variety needed to adapt to the challenges of differing

> Sexual reproduction
> allows the strongest survival traits of a creature (male and female) to
> be passed on to the next generation.

"Strong" doesn't mean anything in this context: Sexual reproduction
allows traits to be reshuffled and then passed on. Success takes care of
itself: The selfish genes that programme the traits that allow the
survival machine to survive and reproduce to pass on those traits are,
by definition, the successful ones.

> The other type of reproduction is
> mitosis, which simply means the division of one cell into two, this
> results in the 'cloning' of the original organism. This 'exact copy' is
> not likely to have the same ability to survive as the creature made as
> a result of sexual reproduction has.

Well, many organisms still reproduce by cloning, and have been doing it since
life began; so cloning has been successful and is still with us (as a
form of reproduction; as GROWTH it is occurring in every cell of an
organism even if it reproduced sexually). So the earth still has plenty
of niches where reproduction by cloning is still quite successful.
(A "niche" is just an organism's local environment: the polar bears is
the frozen North, the halibut's is the sea and the amoeba's is a drop
of moisture). But other forms of reproduction have evolved, because
adapting to other niches required a quicker means of rolling the genetic
dice. The recombinations that occur in reduction divisions and sexual
fertilisation provided that extra source of variability.

> It is important the we produce bodies which are survivors because they
> are vehicles for replicators (genes).

Who is it "important" to? The genes are "selfish" but they are also
mindless: Nothing can be "important" any more than it can be to a stone
-- or to a car: When you say "it's important for your car that its oil
get changed regularly" what you really mean is that it's important for
YOU, if you need to use your car, that it should have regular oil
changes. But although we survival machines are the "vehicles" of our
selfish genes, it's wrong to think of them as the kind of thing anything
can be important to. WE are the ones to whom things are important.

> In fact genes control embryonic
> development, which means that they are partly responsible for their own
> survival in the future.

The selfish genes and their environments are COMPLETELY "responsible"
for their survival or nonsurvival, because that's what survival means.
It's all right to use human-purpose talk ("important", "responsible") as
long as you know that this is just shorthand for genetic lotteries and
cell-building programmes in a complex environment.

> We then went on to discuss the Environment of evolutionary adaptiveness
> (EEA)( otherwise known as the "original' environment ). The point was
> made that most human changes in the last hundred million years have not
> been as a result of evolutionary change.

No, we were still evolving furiously 100 million years ago; it is in the
latest hundreds of thousands of years that human beings gained so much
behavioural flexibility and control in their environments that adaptive
changes occurred in their behavioural PRACTICES, which were passed on
from generation as culture, rather than as hard-wired changes in the
genetic code.

But the most important distinction between now and the EEA is that it
is usually misleading to ask about what might be the adaptive advantage
of this or that trait today: chances are that its adaptiveness was
established long ago, when our environment "shaped" the brains we have
now, through the constraints it put on the success of our selfish genes

> This can be illustrated by
> examining proximal and distal changes in the environment. The argument
> is that in the original environment distal changes brought about
> changes in evolution (the child eating sugar for energy) and in today's
> environment changes are bought about as a result of proximal
> changes,(the child eating sugar because it tastes good).

Not quite: In the EEA, when sugar was rare, those who sought it and ate
it abundantly whenever they could had the energy to escape predators.
Those who were indifferent to sugar got caught and are no longer with us
to tell their tale. The distal (or ultimate) cause of our sugar-eating
habits is the energy advantage it gave our ancestors. But then, as now,
the proximal reason we eat it is that it tastes good. (Our selfish genes
then built us so as to make it taste good to us.)

> Changes are
> brought on as a result of psychological, rather than survival needs.

Today many of our behaviours have nothing to do with the EEA; but with a
little analysis, you can still guess what the EEA survival needs were
that made us what we are today. I have a craving for sugar because it
tastes good; not to raise my blood sugar, or, even less, to raise my
blood sugar so that I am energised to run from an attacking tiger if
need be. We just crave it because it tastes good.

Most of the effects of strategies that were successful in the EEA are
detectable today only as the emotional things beyond our control:
hunger, thirst, lust, love, fear of dark (or heights, or snakes),
jealousy, and perhaps even more subtle emotions such as ambition, pride,

In sociobiology you have to learn to make these everyday things
"strange," and ask: why are we like this?

> This means that different species and individuals within a species all
> adapt separate ways of achieving their goal. Ultimately this means that
> some creatures have stronger survival genes than others.

Nothing about stronger survival genes: Some genes programme successful
vehicles, some don't. And only the survivers survive.

> This results
> in competition, the survival of the fittest, I suppose. However, it has
> been found that it is not only the fittest who are more likely to
> survive, but also 'cheats'.

If cheats survive then they are the fittest!

> Cheats invade other creatures by
> pretending to have the same traits as them and therefore surviving.

A butterfly whose colouring imitates frightening eyes and scares bird
predators away (I am inventing) is a "cheat", but it survives.
"Cheating" is a useful concept when you are trying to think in terms of
evolutionarily stable strategies (ESSs):

> Cheats are not found in an environment where an evolutionary stable
> strategy (ESS) exists.

Unless cheat genes are there in a balanced equilibrium with noncheats --
especially inside the same survival machine: "cheating" by the way, is
not a moral judgement here, but simply contrasting those genes that
follow a rule and those that do not.

> Dawkins describes an ESS as a strategy which, if
> most members of a population adopt it, cannot be bettered by an
> alternative strategy. It means that the environment is working as a
> unit to try and make things better for the whole species. This
> ultimately means that it is impossible for the species to be fooled by
> unwanted cheats.

You're thinking of it as a purposive thing, but it's not. An ESS is an
ESS because it succeeds and nothing succeeds against it. There is no
evolutionary factor that amounts to being "better for the species."
We may describe it that way, but what it really happening is just the
selfish genes riding around in their survival bumper-cars, some making
it to the next generation, some not. If they happen to code for a
strategy, then this strategy could be a stable one or an unstable one.
If it is unstable, it will eventually be bettered and will fail. If it
cannot be bettered, it will flourish (until the environment changes in
some way and destabilises it).

> (I'm a bit confused on this topic, it seems to me that there is not
> much difference between an environmentally stable strategy and
> straightforward altruism). Especially as when reading one of Dawkins's
> examples, he describes the digger wasp who basically puts her life at
> risk to provide shelter and food for a succession of her larvae. Surely
> if this is a prime example of a species acting in an evolutionary
> stable strategy then it can be associated with almost all species?!

The altruism of the digger wasp is an example of inclusive fitness, not
particularly of an ESS (though every genetic rule can probably be
thought of in terms of ESSs). The digger wasp is sterile, hence cannot
pass on its genes. However, it is a close relative of the larvae, some
of which WILL be fertile and will pass on those SHARED genes. So it
makes sense for the digger wasp to dedicate itself to rearing its
sisters and brothers to the age where they can pass on their shared
genes, otherwise neither of them makes it into the next generation.

To think of it as a (trivial) ESS, think of two kinds of (sterile)
diggers: one kind eats well, does no work, lives to a ripe old age, and
dies. Besides its own death, it has also allowed the death, by neglect,
of hundreds of sisters, some of them fertile. Another digger wasp (and
obviously one with different selfish genes from those of the
couch-potato digger wasp) works hard to feed and protect its younger
sisters. Who makes it into the next generation to pass on its

Now sterile castes are an especially exotic and extreme case of
altruism. (The selfish gene that even collaborates in creating a sterile
vehicle is already being altruistic!) That is why you have to think not
only of the survival of the gene in the sterile sister, but also the
survival of the same gene in its fertile sisters. The fertile and the
sterile sisters all come from the same original cell; any of the sterile
ones could have grown into fertile ones. The critical factor was the
chemical environment at the stage in their growth where the "switch" was
set for fertility or sterility. (I'm inventing now, as I don't know the
real details:) If at that critical point, there was a diffusion of
hormone from a fertile queen -- usually much bigger than all the rest --
then the embryos all set the sterile switch. If there was not, then some
embryos were switched to fertile and then fought it out as they grew
until only one fertile one survived, grew huge, and did the egg-laying
for its entire extended family.

Let's say that the combat between growing queens is a disadvantage for a
whole hive: no one is laying eggs; there is risk of predators invading;
the females are wasting their bodies being neither queens nor servants,
but simply combating one another. This might be useful occasionally to
ensure that the queen's genetic "line" is a robust one (tested by
beating here rivals) but mostly everyone is better off when it's all
settled and everyone gets back to the business of passing on their
selfish genes.

Something like this happens even in our bodies: Only our sperm and eggs
are "fertile," passing on their selfish genes. The rest of the cells
are just making sure the survival machine of which they are parts
succeeds in surviving and reproducing. The wasp colony is somewhere
between the completely subjugated "sterile" cells that all but out germ
cells are, and families of organisms, like us, in which all members are
fertile. All THREE count their success in terms of INCLUSIVE fitness of
the close kin in the gene pool rather than purely on the basis of
individual fitness.

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