Transcript evolution concepts

Evolution: Basic Principles
Evolution: Change over time; decent with modification
Natural Selection: Primary mechanism producing
evolution (change over time). There are other
mechanisms such as: sexual selection, social
selection, drift.
Basic principles of NS:
1.
Variability: stuff varies
2.
Heritability: variation is passed on genetically
3.
Competition: limited resources
4.
Selection: some variations are advantageous in
securing limited resources and tend to passed on
more than others = change over time
Spencer’s misleading summary of NS: “survival of the
fittest.”
Terms and concepts
Mutation: copying error in genetic transmission. Provides the variability upon which
selection can operate. Most mutations are neutral or detrimental, but occasionally
a beneficial. Are mutations entirely random?
Fitness: Differential reproductive success
Future Blindness: Creatures are adapted to past conditions. The best bet on what the
future is going to be like is the past. But that may not always be true.
Chance and law: chance – the future; mutations. Law – traits that increase fitness will
get passed along, those that detrimental to fitness will be selected out.
Preadaptation: NS can only work with what it is given, traits and structures “designed”
originally for one purpose must be re-fashioned for later ones. This places limits on
future adaptability. Critical question: does a creature have traits whose
preadaptations allow it to be re-molded to met current challenges? If so, it might
survive, it not, it may go extinct. Ex: Humans has pre-adaptations that allowed for
bi-pedalism, large brains, symbolic functioning, not for flying.
Other key concepts
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Modern Synthesis: (neo-Darwinism) combo of Darwinian selection with
Mendelian genetics.
Adaptations: inherited, phenotypic solutions to adaptive problems
Byproducts: non-adaptive incidental tag-alongs to adaptive traits. Navel is
byproduct of adaptation of umbilical connection of mammalian mother to
offspring.
Noise: Random non-adaptive characteristics of adaptations or byproducts. Inny vs.
outie navel; dry hair, frizzy hair etc.
Exaptation: (closely connected to pre-adaptation) adaptive trait or structure
whose original function was different what it currently performs (human inner-ear
bones originally jaw bones of reptiles)
Sexual selection
Some traits may actually be detrimental to survival
but provide an advantage in mating.
Sexual selection: intra-sexual competition
• Typically male-male
competition for mates,
resources, and status.
Evolutionary basis for male competition
• Gamete size: ultimate determinant of “malesness” and
“femaleness.” Leads to differences in parental investment.
(cheap sperm vs. expensive eggs)
• Parental investment : any investment in current offspring
that precludes investment I future offspring. (mating vs.
parenting effort)
• Parental certainty: extent to which on can be assured that
offspring carry one’s genes. (paternal vs. maternal
certainty); high for females, low for males
Intra-sexual coalitional competition
• Chimpanzees are especially wellknown for forming male
coalitions to challenge other
males for dominance.
More concepts
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Domain specificity: A psychological adaptation is specific to
an adaptive problem, does not apply generally to a range of
potential problems. Ex: cheater detection mechanism.
Controversy as to how widespread this type of design is.
EEA: Environment of Evolutionary Adaptiveness. The original
selection pressures which shaped the present adaptation.
Inclusive fitness: W.D. Hamilton – fitness should include not
just direct offspring but kin offspring as well; gene’s eye view
of evolution
Connection to sociobiology: EP – greater emphasis on
psychological mechanisms and less on current adaptive
significance. Humans as “adaption executers, not fitness
maximizers.”
Key concept: NS cannot make you have alot of offspring, it
can only motivate you to engage in those behaviors that in
the past were associated with higher rates of reproduction.
Social Selection
• Some traits help animals get along better in their social
groups which in turn increases their survival and
reproduction. Ex: more socially skilled female baboons tend to
have more surviving offspring.
Traits: Evolutionary origins
• Homologous traits: shared by a species because of common
ancestry (ex: high EQ; sociality; tool use, present in humans and
other apes inherited from common ancestor, “ancestral” traits).
• Analogous traits: traits shared because of similar selection
pressures (“camera” eye design in human and octopi). Evidence for
convergent evolution.
• Derived traits: traits unique to a species because of particular
selection pressure faced during its evolutionary history
(hairlessness, habitual bipedalism, tool dependency, in humans).