History of Evolution and
Human Behaviour
Evolution before Darwin
Evolution
• Change over time in organic (living)
structure
Jean Pierre Antoine • Causes of species change
de Monet de
• Natural tendency for organisms to
advance to a higher form
Lamark (1744• Inheritance of acquired characteristics
1829)
Baron Georges
• Catastrophism
Léopold Chréitien
• Species go extinct in catastrophes and
Frédérick Dagobert
are replaced by new species
Cuvier (1769-1832)
Lamarkian Evolution
Natural
tendency for
organisms to
advance to a
higher form
• Violates the Naturalistic fallacy
• Words like “higher form” give a value
judgment to each organism and it’s closeness
in relatedness to humans
• Different organisms have specialized for
different environments
• Degree of specialization does not indicate the
degree to which something has evolved
Inheritance of
acquired
characteristics
happens via
epigenetics, but not
how Lamark
thought…
• Animals struggle to survive
• The struggle makes the nerves secrete a
fluid that enlarges the organs involved in the
struggle
• Strivings are passed down across
generations
Darwin’s Theory of Natural Selection
Goals
• Explain why living organisms change in form
over time
• Explain how new species emerge
The Beagle Voyages (1831-1836)
• Galápagos Islands
• Each island had a different species of finch
• Darwin thought they each had a common
ancestor
• Diverged because of differences in island
habitat
• Geographic variation in species was pivotal to
Darwin’s theory
Darwin’s Puzzle
What accounts
for why species
change?
Natural Selection
• Variation
• Inheritance
• Selection
Variation
Organisms vary in phenotypic quality
• Wing length
• Trunk strength
• Bone mass
• Cell structure
• Fighting ability
• Defensive ability
• Social cunning
Variation provides the raw material for evolution
Hawaiian honeycreepers
Inheritance
Only some
variations are
inherited
• Lemark believed all acquired traits were inherited
• Darwin believed variations such as wing deformity caused by
environmental accident are not inherited
• Only those inherited traits play a role in the evolutionary
process
We now know that
genetics are the
mode of
inheritance
• There are also epigenetic phenomena, but this plays a much
smaller role
• Darwin may or may not have read Mendal’s work on genetic
inheritance, but this was not mentioned in Darwin’s writing
Selection
Organisms with
some heritable
variants
Leave more
offspring than those
that have other
heritable variants
Because variants
help with
• Survival
• Reproduction
Survival
Survival is not the
goal of evolution
Reproduction is the
driving force
Differential
Reproductive Success
• Survival only alters
evolution when it affects
reproductive success
• Variation in prevalence of
heritable traits that
increase or decrease
reproductive success
across a population of
conspecifics
Darwin’s Theory of Sexual Selection
• Certain traits did not fit Darwin’s
theory of Natural Selection
• Some traits had nothing to do with
survival
• Peacock feathers was one example
• Peacock Feathers
• Only males have
elaborate trains
• Energetically costly to
produce
• Attracts predators
• Reduces ability to evade
predators
Darwin’s Theory of Sexual Selection
Why are there
structures that have
nothing to do with
survival?
Why do the sexes
often differ so much
when they share the
same problems of
• Procuring food
• Fending off predators
• Combating diseases
Darwin’s Theory of Sexual Selection
Intrasexual competition
Intersexual selection
• Competition between members on
one sex
• Outcome contributes to mating
access to the other sex
• Winners of competition mate
more often than losers
• Traits that aid in successful
competition increase in
frequency across generations
• Preferential mate choice for
desired characteristics
• Evolutionary change occurs
because those possessing the
characteristics are chosen as
mates
• Those traits are passed on to
subsequent generations at higher
frequencies
Other Causes of Evolutionary Change
Genetic
Drift
Artificial
Selection
• Random changes in genetic makeup of population
• Mutation
• Founder effects
• Random Bottlenecks
• Grafting
• Animal Husbandry
• Breeding/Crossbreeding
• Cloning
Founder Effect
Loss of genetic variation
that occurs when a new
population is
established by a very
small number of
individuals from a larger
population.
Bottleneck effect
Population bottlenecks occur when a
population’s size is reduced for at least one
generation.
• Genetic drift acts more quickly to reduce genetic variation
in small populations
• Bottleneck can reduce a population’s genetic variation by
a lot, even if the bottleneck doesn’t last for very many
generations.
Artificial Selection
Intentional breeding of organisms
Evolution via natural selection
Not
intentional
Not
forward
thinking
Only acts
on variants
that exist
Does not
predict the
future
Does not
foresee
future
needs
Evolution is gradual
The speed of
evolutionary
change is slow
Punctuated
Equilibrium
Dozens
Periods of no or
very slow
evolutionary change
Millions
Followed by periods
of rapid
evolutionary change
of Generations
Common questions
Did humans descend from
apes?
How are partial adaptations
useful?
Where are the missing links?
Why have humans stopped
evolving?
Isn’t it just a theory?
Humans did not evolve from apes
Humans did not evolve from apes
How are partial adaptations useful?
A partial wing can’t fly
Partial wings
• Why evolve a partial wing?
• Provide warmth
• Aid in mobility in catching prey
• Jumping
• Stabilization
Argument from ignorance
(Dawkins, 1986)
• Difficulty in imagining an adaptive
function for a trait is not evidence
against such forms having evolved.
Missing Links
• There is no such thing as a missing link
• The term “missing link” comes from the idea that we haven’t found
transitional fossils between humans and apes
Humans continue to evolve
Wisdom teeth
Cesarean Section
• Humans are being
born without wisdom
teeth
• Evolution supports a
use-it or lose-it policy
• Processed foods
alleviate the
requirement for
wisdom teeth
• Selection on skull size
at birth is reduced
• Head size at birth is
allowed to grow
Lactose tolerance
• Developed 3000
years ago in East
Africa
Isn’t it just a theory?
Fact
Hypothesis
Law
Theory
• In science, an observation that has been repeatedly confirmed and for all practical
purposes is accepted as "true." Truth in science, however, is never final, and what is
accepted as a fact today may be modified or even discarded tomorrow.
• A tentative statement about the natural world leading to deductions that can be tested. If the
deductions are verified, it becomes more probable that the hypothesis is correct. If the deductions
are incorrect, the original hypothesis can be abandoned or modified. Hypotheses can be used to
build more complex inferences and explanations.
• A descriptive generalization about how some aspect of the natural world
behaves under stated circumstances.
• In science, a well-substantiated explanation of some aspect of the natural
world that can incorporate facts, laws, inferences, and tested hypotheses.