Debates Lecture Notes

From: Stevan Harnad (
Date: Fri Feb 28 1997 - 20:01:45 GMT

> Date: Thu, 27 Feb 1997 13:49:40 GMT
> From: katie turner-samuels <>
> Subject: today's lecture
> Stevan,
> where can I find information on each lecture, particularly
> the overheads that you said were on web? All I can find is
> the skywriting.
> Katie T-S

Here they are. They'll be archived in the Skywriting.


Natural Selection:

Artificial selection occurs when we selectively breed (and inbreed),
say, dogs so they will have certain traits such as size, strength,
aggressiveness, friendliness to people, etc. It is accomplished by
selectively mating the dogs with those traits to one another, and
and not allowing those dogs who lack the trait to reproduce. If
the traits for which the select breeding is done are GENETIC ones
(and most are) then selective breeding can produce the huge
variations you see in dogs.

Natural selection occurs when selective breeding is done by the "Blind
Watchmaker" (i.e., the environment): the number of organisms with
the traits that help survive and reproduce become more numerous
and the traits that deter survival and reproduction become less

Nothing succeeds like success: Adaptive traits are the ones that are
passed on because what it MEANS to be an adaptive trait is that it gives
its "vehicle" (the organism that has that trait) better chance to
survive and reproduce than the organisms without it.

"Fitness" is success in surviving and reproducing.

The Environment of Evolutionary Adaptedness (EEA):

the original environment in which the trait in question evolved;
not to be confused with the present environment.

traits may have been adaptive in the EEA but they may be neutral
or mildly negative now

unless they are negative enough to have a systematic effect
on survival and reproductive success, they will remain

Example: Sugar scarcity and the "sweet tooth": This was
adaptive in the EEA but is no longer adaptive in the modern

Proximate vs Ultimate Causes/Explanations:

An ultimate explanation is an explanation in terms of ultimate
causes. Ultimate causes are Darwinian, adaptive causes. That
means some condition that influenced survival and reproduction
in such a way as to select one trait over another. This
selection would take place in the EEA and is called "natural

Example: a sweet tooth (a tendency to eat all the sugar we can get)
arose because sugar was rare in our EEA and important for energy,
hence survival and reproduction

A proximate explanation is an explanation in terms of proximate causes
in the present environment. In sociobiology, proximate causes are
psychological ones.

Example: We eat sugar because it tastes good, not because we think
it will help us survive and reproduce

Inclusive Fitness:

Natural selection operates at the level of the gene: the genes that help
their "vehicle" (the organism) to survive and reproduced are passed on.

Genes are "selfish," which means they could not code for traits that
increased ANOTHER organisms fitness at the expense of its own. Any
such "altruistic" gene would immediately disappear, because it would be
the OTHER organisms genes that were past on instead of the "unselfish"

There is one prominent exception, namely kinship: A child has half
the genes of its mother, and the child's survival is the most important
way in which the mother's genes are passed on. So if a mother had a gene
for infanticide or child abuse, that gene could not be passed on.
So it is adaptive for mothers (and fathers, if it is very likely that
they ARE the fathers) to sacrifice their resources (food, child-rearing)
for the sake of their offsprings' survival to reproductive age.

Offspring are not the only relatives, however. Based on the proportion
of the same gene shared, it would make evolutionary sense for an
organism to be prepared to "lay down its life" for an MZ twin,
2 DZ twins or siblings, 4 cousins or half-sibs, etc.

So organisms have traits to enhance not only their INDIVIDUAL fitness,
but also their INCLUSIVE fitness; the fitness of near kin is part
of an individual organism's inclusive fitness.

Sociobiology makes quantitative and qualitative calculations of
inclusive fitness, but because these calculations are nor PREdictive but
RETROdictive (given success, it tries to explain why it happened),
it has problems of testability. These are methodological problems, and
with many traits they are negligible, but with others they are not
negligible. This is what has generate the criticism of sociobiological
theories as Just-So stories.

Evolutionarily Stable Strategies

"Strategies" are always ultimate rather than proximate; hence
they are not CONSCIOUS strategies of organisms but "blind"
strategies of genes.

A strategy is not evolutionarily stable if it can be "invaded" by
another strategy. An example would be the evolution of a green
spot on the forehead that would signal that the organism had a certain
gene. Then all organisms who have the green "trait" could have
a proximate desire to help organisms that also had the green spot.

This is not an evolutionarily strategy because it is easily "invaded" by
organisms that lack the green gene but have the green spot, because the
ones with the real green gene would help the false green gene organism
until the true green trait was lost altogether -- and then nothing
would maintain the useless false green gene either.

Evolutionarily stable strategies are those that cannot be "invaded" in
this way.

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