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ANTH201 > 2 - Natural Selection > Flashcards

2 - Natural Selection Flashcards

1
Q

Mechanism for organic evolution

A

Adaptation by natural selection

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2
Q

Key points of natural selection

A
  • Species can change
  • Species can evolve from other species through mechanism of natural selection
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3
Q

Darwins three postulates

A
  • Competition: Individuals compete because resources are finite
  • Variation: Individuals vary in ways that affect their ability to survive (i.e. fitness)
  • Heritable: Some of this variation is heritable
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4
Q

Competition

A
  • Populations can expand indefinitely, but resources are always finite
  • Individuals compete for limited resources (e.g. food) within a particular habitat
  • Not all individuals survive long enough to reproduce
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5
Q

Variation

A
  • There is a variation among individuals in a population
  • Some individuals will possess traits that make them more successful
    (i.e. higher fitness)
  • Those traits allow them to survive and reproduce, or produce more offspring
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6
Q

Heritable

A
  • Differences among individuals are transferred from parents to offspring
  • Those advantageous traits will become more common in successive generations
  • In Darwin’s time mechanisms of inheritance still unknown
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7
Q

Conclusion of Darwin’s postulates

A
  • Those individuals who compete well pass on their traits, including those that
    help them to survive/reproduce
  • Those that don’t survive or reproduce less leave fewer of their characteristics
    (disadvantageous traits disappear)
  • Those traits that help individuals to survive and reproduce → adaptations
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8
Q

Natural selection

A

The process that leads to
adaptations when these 3 postulates hold

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9
Q

Adaptation

A

A trait that is shaped by natural selection and allows the individual to survive and reproduce more successfully

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10
Q

Peppered Moth (Biston betularia)

A
  • First appears in mid-1800’s
  • By 1895, 95% B. carbonaria
  • Darker moths (due to variation) less visible to bird predators on trees blackened by soot
  • With Clean Air laws, B. carbonaria declines
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11
Q

Galapagos Finches postulates

A
  • Competition for limited resources in environment (droughts)
  • Variation in traits important for survival (beak depth)
  • Variation heritable
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12
Q

Changing environments causes competition

A
  • Drought leads to failure of seed crops
  • Overexploitation of small seeds
  • Large hard seeds remain causing struggle for survival
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13
Q

Variation in beak depth

A
  • Large beaks confer advantage (differential
    survival)
  • Note that fewer total
    individuals now in population
  • Success of large beaks leads to shift in mean
    beak size in population
  • Variation is heritable
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14
Q

Types of selection

A
  • Directional selection
  • Stabilising selection
  • Disruptive selection
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15
Q

Directional selection

A

Mean shifts after selection

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16
Q

Stabilising selection

A
  • Mean remains the same
    before and after selection
  • Preserves equilibrium
17
Q

Stabilising selection in finches

A
  • Selection that preserves status quo
  • Some disadvantages to larger beaks
  • Equilibrium
  • Those at tails eliminated (selection still active)
18
Q

Disruptive selection

A
  • May eventually lead to two populations with distinct means
19
Q

Natural selection can’t explain the evolution of complex traits misconception

A
  • Complex adaptations don’t evolve all at once
  • e.g. A computer simulation of the evolution of the eye generates this sequence of
    forms
  • Demonstrates each change, building on previous small changes, can produce complex adaptations
20
Q

Convergent evolution

A

Live in similar habitats and so are subject to similar selective pressures

21
Q

Natural selection occurs at the level of the individual misconception

A
  • Occurs at level of population
  • Changes in gene frequencies
  • More interested in how average beak size changes over time (not how any one individual’s beak looks)
22
Q

All traits are adaptive misconception

A
  • Not all traits are adaptations
  • Only an ‘adaptation’ if it contributes to fitness
  • Some traits are former adaptations (e.g. appendix)
  • Others are just traits (e.g. human chin)
23
Q

Evolution is not ‘progress’

A
  • Evolution does not always progress in one direction
  • No such thing as “better”
  • ONLY better suited to a particular environment.
  • So, if the environment changes then gg

ANTH201 (6 decks)

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