Evolution By Natural Selection

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Chapter 2

• Evolution By Natural Selection

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Natural Selection

• Occurs when genetic variation among individuals
  in an environment causes some individuals to have
  better survival and reproduction.
• Genes that code for characteristics that
  decrease the chances of survival and reproduction
  in current and future generations are eliminated.
• Example genes that cause individuals not to
  reproduce will be selected against

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• Natural selection has no plan, no goal, and no
  direction.
• There are just genes that increase and decrease
  in frequency depending on how they affect
  reproductive success.

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Groups vs. Genes in Natural Selection

• Individuals are actually vessels created by
  genes for the replication of genes.
• Genes that cause suffering while increasing
  reproductive success will be selected for, hence
  natural selection does not cause harmony.
• Group selection is not common - Lemmings dont
  kill themselves for the good of the cause.

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Kin Selection

• Genes can get themselves into future generations
  by having children, or by helping close
  relatives.
• Simple Economics-Selection favors helping
  relatives if the cost of helping is less than the
  benefits to the relative.
• Cooperative relationships also occur in nature
  during reciprocal exchanges-e.g. mutualism

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Survival Of The Fittest-Not Exactly

• Survival is of no consequence in and of itself.
• Survival increases fitness only if it increases
  later reproduction.
• Example Animals and plants that reproduce once
  and die.

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What is Fit?

• Healthiest, Strongest, Fastest?
• Not Necessarily
• Fitness depends on the current environment-individ
  uals are only fit in reference to their
  environment.
• What is advantageous in one environment may be
  disadvantageous in another.
• Fitness always involves compromises.

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Natural SelectionPerfection?

• Natural Selection does not create perfection or
  the best path for a species long term survival.
• Usefulness of a trait doesnt mean it will
  evolve-humans will never sprout wings and fly
• Natural Selection does select among the minor
  modifications of a trait over many generations so
  that the trait approaches the functional ideal.
• Birds have optimal wing lengths.

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Evolution Involves Compromises

• Natural Selection does not cause perfection in
  every trait simultaneously.
• Compromises are made to achieve the greatest net
  benefit.
• Genes that give an overall fitness advantage are
  selected, even if the genes have negative side
  effects.
• Genes that confer benefits early in life may
  cause aging later in life.

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Evolutionary Hypotheses

• Absurd vs. Functional Hypothesis
• Nose evolved to hold up eye glasses vs. Eyes
  evolving so we can see.
• Functional Hypotheses can lead to new
  discoveries, most hypothesis are not clearly
  right or wrong.

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The Adaptationist Program

• Is a method of investigation that leads to
  functional explanations of human attributes.
• Unknown aspects of human biology could be
  logically explained after suggesting the
  functional significance of a known aspect of
  human biology.

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• Example- Discovery made by considering how
  various features increase fitness.
• Economic Beavers How do beavers know which trees
  to harvest?
• Adaptively was what Gary Belovsky suggested.
• Beavers decide which trees to extract based on
  the trees value, the difficulty in cutting it
  down, and the distance to home.
• Efficient beavers are increasingly choosy as the
  distance from the dam increases.
• Predict that the range and size of trees
  harvested will decrease as distance from the dam
  increases- will harvest trees of an ideal size.
• Prediction was confirmed.

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To really understand human ailments we need to
comprehend what appear as mistakes in design.
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Answering questions about how natural selection
allowed functionally undesirable traits to evolve
in humans can greatly impact the field of
medicine and how we treat diseases.
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