EVOLUTIONARY BASES OF
BEHAVIOR
DARWIN’S INSIGHTS
Wrote On the Origin of Species
 Identified natural selection as the mechanism
that controls the process of evolution
 Attempted to discover why organisms developed
traits that suited them for their environment

DARWIN
Noticed animals vary
 Noted some characteristics are heritable
 Noted organisms reproduce at a pace that
outdoes food supply and other resources
 Therefore: traits that increase reproduction
increase an organisms’ survivability

EVOLUTIONARY THEORY
“Survival of the fittest”
 Fitness: reproductive success of an individual
organism relative to the avg reproductive success
in the population
 2 ways traits contribute to evolution:
 1: survival advantage
 2: reproductive advantage

NATURAL SELECTION

Def: heritable characteristics that provide a
survival or reproductive advantage are more
likely than alternative characteristics to be
passed on to subsequent generations and thus
they come to be “selected” over time
CONTROVERSY
Went against idea of divine intervention in life
 Implied humans are not unique and they share a
common ancestry with other species

REFINEMENTS
Theodore Dobzhansky synthesized Darwin’s
theories with the genetics work of Gregor Mendel
 Contemporary: gene pool shaped by genetic drift,
mutations, and gene flow

ADAPTATIONS
Def: inherited characteristic that increased in a
population b/c it helped solve a problem of
survival or reproduction during the time it
emerged
 Key product of evolution

INCLUSIVE FITNESS
Def: the sum of an individual’s own reproductive
success plus the effects the organism has on the
reproductive success of related others
 Explains paradox of self-sacrifice

BEHAVIOR AS ADAPTIVE TRAITS
Patterns of behavior reflect evolutionary
solutions to adaptive problems
 Camouflaging, fleeing, selective reproduction

PARENTAL INVESTMENT AND
MATING SYSTEMS
Parental investment: what each sex has to
invest—time, energy, survival risk—to produce
and nurture offspring
 Most males contribute little, females contribute
the most

POLYGYNY
When investment is high for females and low for
males:
 Polygyny: mating system in which each male
seeks to mate w/ multiple females, whereas the
female mates w/ only one male
 Favors aggressively competitive males

POLYANDRY
Def: mating system in which each female seeks to
mate with multiple males, whereas each male
mates w/ only one female
 Very rare

MONOGAMY

Def: mating system in which one male and one
female mate exclusively (or almost) with each
other
MISCONCEPTIONS ABOUT
EVOLUTION
1: Evolution is only a theory---evidence to support
is substantial
 2: Evolutionary analyses assume that organisms
have a motive to max reproductive fitness
 3: Evolutionary analyses embrace genetic
determinism
