Evolution by Natural Selection

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Evolution by Natural Selection
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How did life originate? Why are all the species
we see on earth in existence? 3 main ideas
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Creationism
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Seeding theory
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Evolution by natural selection
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In the distant future . . . Psychology will be
based on a new foundation, that of the necessary
acquirement of each mental power and capacity by
gradation. --Charles Darwin, 1859
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Landmarks in the History of Evolutionary Thinking
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Evolution Before Darwin

• Change over time in organic structures
  (evolution)
• Characteristics seemed to have a purpose
  (porcupines, turtles, skunks)

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Jean Pierre Antoine de Monet de Lamarck
(1744-1829)

• Two causes of species change
• 1. Progress toward a higher form
• 2. Inheritance of acquired characteristics

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Darwins Theory of Natural Selection

• The explanatory challenge
• 1. why change takes place
• 2. how new species emerge
• 3. what the functions are of parts

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One clue Malthus more organisms produced than
survive and reproduce, leading to a struggle
for existence
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More individuals produced than can possibly
survive
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Struggle for Survival
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Natural Selection

• Variation
• Inheritance
• Differential Reproduction

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The key to natural selection Differential
reproductive success because of heritable
variants everyone has ancestors, but not
everyone leaves descendants
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Natural selection provided 3 key answers

• Explained change over time (descent with
  modification)
• Explained apparent purposive quality of component
  parts
• United all species into one grand tree of descent
  (including humans)

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Problems That Troubled Darwin

• 1. Phenomena that seemed inexplicable on the
  theory of survival selection
• 2. The existence of sex differences.

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Objections to Natural Selection

• No theory of inheritance at the time
• Hard to imagine utility of intermediate stages,
  and natural selection requires each step to
  benefit
• Beliefs at the time that species were unchanging

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Three Products of Evolutionary Processes

• 1. Adaptations
• 2. Byproducts
• 3. Noise

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Adaptations

• 1. inherited characteristics
• 2. reliably developing in most or all species
  members
• 3. produced by natural or sexual selection
• 4. because they solved an adaptive
  problemfunctionality
• 5. must have contributed to reproductive success,
  directly or indirectly
• 6. need not be present at birth (teeth, breasts,
  beards, desires, etc.)

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One Example of Adaptation Umbilical Cord
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Byproducts

• Characteristics that do not solve adaptive
  problems
• Do not have functional design
• Are carried along with characteristics that do
  have functional design

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Examples of Byproducts belly button
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More Examples of Byproducts

• belly button
• heat from light bulb
• white color of bones
• Attributing intentionality to objects that do not
  have intentionality (sun, clouds)

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Noise random effects due to mutations or
perturbations during development Examples shape
of belly buttonperturbation in roundness of
glass bulb
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Adaptations are the primary products of natural
and sexual selection
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Sexual Selection

• Intrasexual Competition
• Intersexual Selection

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• The sight of the peacock gives me nightmares
  Charles Darwin

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Intrasexual Competition

• competition among members of the same sex for
  mating

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Thought experiment

• Examples in humans of intrasexual competition?

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Intersexual SelectionPreferential Mate Choice
a form of sexual selection in which members of
one sex are differentially attracted to members
of the opposite sex
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Intersexual SelectionPreferential Mate Choice
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Two Kinds Of Causal Questions

• Proximate HOW a mechanism develops and operates
• Ultimate WHY a mechanism evolvedevolutionary
  forces that led to the creation of the mechanism
  the adaptive problem it evolved to solve.

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Causal Question

• Why are men taller than women on average?

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Proximate and Ultimate Answers to Questions

• Why are men taller than women on average?
• Why do people grow calluses?
• Why do people like to eat pizza?
• Why do people get jealous?

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