Intro Mind Notes, Week 7: Evolutionary Psychology
(HMW, Ch. 3, especially pp. 155-190 and 205-210)
A. Darwin's Theory of Evolution by Natural Selection
- The theory explains the improvement of a trait (for example the gradual
clearing of a lens of an eye from one generation to the next) by assuming
that there is selection pressure for that improvement. Selection
pressure is not a force of nature. The "pressure" simply means
that animals that have the improvement are (even very slightly) more liable
to survive and reproduce in their environment than are those that lack
the improvement. Over time, selection pressure causes the successive generations
of a population to gradually increase the proportion of the animals with
the improvement.
- Natural selection will work in any population where: a. There is selection
pressure. b. The organisms "breed true", that is where the offspring
is more liable to share features of their parents than they do with their
non-parents. c. There is a mechanism that insures variation in the population,
for example mutation and/or sexual reproduction.
B. Evidence for the Theory of Evolution
- There is overwhelming evidence that organisms evolve by natural selection.
Pinker mentions two kinds of evidence: evidence from the biological world,
and evidence from mathematical models.
- Among the many examples of organisms known to change their traits through
the process of evolution are domestic animals, the white peppered moth,
Darwin's finches and many bacteria and viruses. For example, it is well
understood that bacteria that infect humans have evolved new defenses against
antibiotics.
- It is possible to model evolution on a computer to show the principles
in action. Mathematical studies show that very small selection pressures
can create very large changes in organisms over long periods of time. Pinker
mentions a computer model that spontaneously creates the structure of an
eye from nothing but the process of evolution.
C. Myths of Evolution
- People sometimes misunderstand the theory of evolution by natural selection
(Darwin's Theory), and mistakenly attack it for reasons that have nothing
to do with what the theory says. To make sure that you understand the evolution
of intelligence, Pinker refutes the following myths about Darwin's theory.
- Evolution is linear. There is no step by step goal directed
aim of evolution, where each organism in the history marches on a narrow
road towards the ascent of man. Evolution creates a tree of life that is
very bushy, where the vast majority of branches die out. The fossil record
of the evolution of hominids (man like apes) is a somewhat random collection
of "uncles", "aunts", "nephews" and "cousins"
on the "family tree", not a sequence of parents grandparents,
great-grandparents, etc.. The idea that we can find missing links between
hominid fossils is misguided.
- Evolution has a goal. Improvements produced by evolution are
not aimed at any goal. A goal has no power to cause evolution to go in
any direction, because this would amount to the future (the goal) affecting
the past, which is incompatible with what we know about the natural world.
It is true that over the 4 billion years that life has evolved on our planet,
some organisms have become larger and more complex. Humans have even become
complex enough to study the natural world and wonder about their origins.
However, it was not the goal of natural selection to produce this sort
of intelligence. Under different circumstances, intelligence might never
have developed on Earth. Intelligence evolved because it gave reproductive
advantages to organisms that had it. However, being intelligent has its
costs for humans: large head, energy drain, the need to learn, and a disadvantage
in speed. Intelligence evolved not because it is good, or desirable, or
the goal of life, but because the benefits happened to outweigh the costs
for certain apes that began to exploit grasslands in Africa. If the conditions
had been a bit different those apes might never have evolved into humans.
- All traits of an organism can be explained by natural selection.
A large number of the features of organisms have no selective advantage.
They may have evolved as "side effects" of other features that
were adaptive that is, that did provide the organism with a reproductive
advantage. Examples of non-adaptive traits in humans include the appendix,
the chin, and the ability to learn the rules of chess. Pinker uses the
term 'adaptationism' for the view that all traits of an organism
are adaptive. Obviously no one believes this brand of adaptationism. Some
people who lean (too far?) in the direction of trying to find adaptive
explanations for traits are also called adaptationists. Pinker's point
is that we should be suspicious of claims that a trait is adaptive until
well-developed evidence is available.
- Natural selection is the only influence guiding evolution. Clearly
physical limitations having to do with the nature of protein, bone, etc.
limit what natural selection can accomplish. Also, accidents either of
mutation or environment change have had their effects. (If volcanos hadn't
wiped out the dinosaurs, there might be no humans today.)
- The creation of features like wings requires big jumps in evolution.
Some people argue that evolution cannot explain wings or eyes because a
partly formed wing or eye is useless and so has no adaptive advantage.
So evolution must operate by fantastically unlikely jumps. A massive mutation
must explain the creation of the first wing. However, the gradual evolution
of structures (solar panels, feathered arms) for one purpose (thermal regulation),
may create structures with a different adaptive advantage (gliding) which
can then be better adapted to that new purpose or even new purposes (flight).
- Natural selection is trivial. Some people say that survival
of the fittest is not a meaningful principle at all, because by 'fittest'
you presumably just mean whatever survives. So the idea that animals are
selected for traits that improve their chance to reproduce, simply boils
down to the claim that traits that survive survive. This objection misses
the point about what natural selection is supposed to explain: namely the
complex structures (like the human brain) which we find in the animal kingdom.
Darwin's claim is that those structures evolved gradually because along
the way those structures provided a selective advantage to the organism
in its environment. This explanation is far from trivial, and could be
false.
- Humans have evolved beyond instinctive behavior. Humans have
not left instinct behind. One might ague that a lot of what makes us smart
is the refinement and elaboration of instincts.
- Humans are still evolving. Humans have evolved very little since
the dawn of history (about 5,000 years ago). There has not been time for
selection to cause much change, and the blossoming of culture and technology
has removed selection pressures. In the modern age, ability to reproduce
is no longer linked to traits such as intelligence, strength, eyesight,
physical coordination, etc.
- Human desires and goals are all related to the need to reproduce.
The fact that people can want to limit the size of their families, or decide
on suicide shows that human goals and the "goals" of natural
selection do not coincide. This does not refute Darwin's theory. That theory
was only designed to explain the emergence of human abilities such as problem
solving, linguistic communication, physical coordination, etc. Once these
abilities have developed they take on a life of their own. The organism
is now abe to formulate its own goals: (e.g. a luxurious life style with
few or no kids) which have nothing to do with reproduction.
- Human Culture evolves by natural selection. There are some analogies
to be drawn between genes and what Dawkins calls memes (that is
cultural ideas that are passed from one generation to another). Memes do
compete for our energies, and they do grow and die. However, it is a distortion
to look at the evolution of memes as a process of natural selection. If
it were one, there would have to be a reproductive process with random
variation in the "offspring"; and there would have to be selection
pressures on memes that effect their probability of reproducing. Neither
of these ideas can be taken very seriously. Instead Pinker likens the spread
of memes to infectious agents like bacteria or viruses. This is not natural
selection because natural selection is a process that explains the origin
of new structure that has a reproductive purpose. All we have in the case
of memes, however is the spread of the same item into new "territories".
D. Why Intelligence is the Product of Natural Selection
- Natural selection is the only naturalistic explanation we have for
the development of any complex design in the animal kingdom. Since the
brain is complex and designed, it is a product of natural selection.
- Some say that mere random changes (genetic drift) can create useful
structure. However without natural selection, there is no explanation for
why useful structure would be preserved through time. Whatever structure
random forces create they very quickly destroy.
- Some look to chaos theory for a source of structure, and some have
suggested that such complexity can replace natural selection in the explanation
of biological structure. But although those structures might be usefully
employed during evolution, you still need natural selection to refine and
preserve them.
E. The Evolution of Information Processing in the Brain
- What the brain is able to do is the product of our genes and the interaction
of the brain with the environment during a process of growth and learning.
It is meaningless to try to sort the brain's abilities into those entirely
created by genes (nature) and those entirely created by learning or interaction
with the environment (nurture).
- It is not at all hard to see how a neural net like the brain can evolve.
All that is required is that the settings of the synaptic connections be
controlled by our genes, and that our genes are passed from one generation
to another in a process of sexual reproduction, where parents' genes are
mixed in new combinations in their offspring. Natural selection, operating
over many generations, can gradually alter the initial synaptic connections,
thus creating new behavior, which new adaptive advantages. So new mental
abilities can arise from evolution without learning.
- Pinker also believes that the brain uses a symbolic processor to accomplish
such tasks as reasoning, and understanding language. Can such a processor
evolve? Pinker points to evidence from genetic programming that suggests
that it can. Garson pointed out that his research suggests that we should
be less optimistic and Pinker is about the evolution of programmed symbolic
processors, although it is certainly not out of the question.
- The Baldwin Effect illustrates the complex interaction between
genetically fixed abilities and learned abilities in the process of evolution.
One thing evolution can do is develop brain structure that makes it easier
for the organism to learn the kind of task it needs to learn to adapt to
its environment. As succeeding generations get better and better at learning
the task, there is selection pressure for the brain to acquire the needed
structure genetically so that it will have less to learn. So over the course
of history it looks as though the organism acquires new genetically programmed
skills by engaging in a learned activity. (It is entirely contrary to Darwin's
theory to believe that structure in an animal's offspring is determined
by what the parent did during its life. That was Lamark's theory of evolution
and it has been thoroughly refuted. A giraffe stretching its neck to get
at leaves in high trees does not have a higher probability to have offspring
with linger necks, as Lamark believed. However, the Baldwin effect appears
to provide for a process that resembles what Lamark thought might happen,
for in this case the practice of a learned skill in earlier generations
evolves into a genetically fixed ability. Although this resembles Lamark's
idea, the Baldwin effect can be explained entirely within Darwin's theory.
F. The Cognitive Niche
- Every organism evolves to exploit a niche (way of interacting with
the environment). Baleen whales have evolved to become very efficient strainers
of small organisms out of seawater, while ducks have evolved to strain
algae and other plants out of pond water, etc..
- Humans have evolved to exploit what Pinker calls the cognitive niche.
The cognitive niche is not a particular way of acting to solve a narrow
set of problems. What makes the human strategy for survival so powerful
is its flexibility and generality. The trick was to evolve a mind that
was able to understand how the world works in general and to formulate
plans to use what is known about the world to promote survival. The cognitive
niche is a way a life that requires the storage of complex information
about the world (like where game or fruit is to be found) and the development
of flexible and changing strategies to exploit that information (like hunting
strategies, or plans to pick store and share the fruit).
- By focussing on the power of information processing to develop resources,
humans have hit on a general purpose intellectual abilities rather than
a collection of specific skills (like how to crack nuts with your teeth).
Instead the general abilities that allow humans to fill the cognitive niche
have lead to the development of tool use, language, and other innovations
in culture and social life that allow human societies to survive virtually
anywhere on Earth.