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33 Cards in this Set
- Front
- Back
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Evolution
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is the change over time in allele frequencies in a population of organisms.
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Two major points:
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Current species are descendants of ancestral species
- ancestral species differ from modern species. Natural selection provided a mechanism for this evolutionary change. |
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Aristotle (384-322 B.C)
Old Testament of the Bible Carolus Linnaeus (1707-1778) |
Opposed evolution
species fixed and unchanging scala naturae Species individually designed by Creator and perfect Seemed to corroborate Aristotle’s views Many scientists of 1700’s believed that Creator had designed each species for a specific purpose Binomial naming system Classified species into hierarchy – increasingly complex, nested categories Similarity between species reflected pattern of creation rather than evolutionary relatedness |
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Paleontology
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study of fossils in sedimentary rock in layers or strata
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Cuvier
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opposed idea of gradual evolutionary change but observed extinctions in fossil record
Opposed evolutionary change; advocated catastrophism Repopulation via immigration |
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Geologist James Hutton (1726-1797)
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perceived that changes in Earth’s surface can result from slow, continuous, gradual mechanisms still operating today
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Geologist Charles Lyell (1797 – 1875)
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Took Hutton’s ideas and incorporated into his principle of uniformitarianism = mechanisms of change are constant over time
Same geological processes operate today as in past and at same rate |
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Thomas Malthus
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Essay on the Principle of Population (1798)
Populations have potential to increase geometrically Typically doesn’t happen in real populations Limited resources Competition Both Darwin and Wallace proposed that best adapted individuals in the population would ‘win’ the competition (competitive advantage) next generation would have more individuals well adapted to environment |
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In 1809, Lamarck hypothesized that
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species evolve through:
use and disuse and inheritance of acquired traits Mechanisms unsupported by evidence (modern genetics) Also thought evolution occurred due to an innate drive to become more complex |
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The phrase descent with modification summarized three broad observations:
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The unity of life
The diversity of life The match between organisms and their environment |
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Darwin’s two main ideas:
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Descent with modification explains life’s unity and diversity
Natural selection explains the observable patterns of evolution |
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Observation #1:
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Members of a population often vary greatly in their traits
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Observation #2:
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Traits are inherited from parents to offspring
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Observation #3:
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All species are capable of producing more offspring than the environment can support
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Observation #4:
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Owing to lack of food or other resources, many of these offspring do not survive
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Inference #1:
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Individuals whose inherited traits give them a higher probability of surviving and reproducing in a given environment tend to leave more offspring than other individuals
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Inference #2:
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This unequal ability of individuals to survive and reproduce will lead to the accumulation of favorable traits in the population over generations
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Natural selection
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the change in an allele’s frequency over time based on that particular allele’s impact on survival and reproduction.
An individual that is best adapted to survive due to advantageous alleles leaves more offspring, and as a result, the next generation is enriched with the same advantageous alleles. Over time, natural selection acts to increase the overall fitness of the population individuals carrying advantageous alleles reproduce more than individuals not carrying advantageous alleles. |
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4 Important Points About Natural Selection
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1.Individuals do not evolve - populations evolve over time.
2.Natural selection can act only on heritable traits. Environmental factors vary from place to place and from time to time 3.A trait favorable in one environment may be useless or detrimental in another environment. Local environment determines which traits will be selected for or against in any population 4.Natural selection does not create new traits, it edits or selects for traits already present in the population |
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Positive Selection
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natural selection that increases the frequency of a favorable allele
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Negative Selection
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natural selection that decreases the frequency of a deleterious allele
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Balancing selection
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natural selection that keeps an allele at an intermediate frequency in the population
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If graph occurrence of a particular trait over time, selection patterns emerge:
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Stabilizing selection
Directional selection Disruptive selection |
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Stabilizing selection
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selects against extreme
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Directional selection
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against one of the 2 extremes
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Disruptive selection
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selects against the mean
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directional selection
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Successful genotypes are selected by the breeder, not through competition
Examples often in agriculture |
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Sexual selection
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increases individual’s reproductive success
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3 evolutionary mechanism
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Migration
Mutation Genetic Drift |
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Migration
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movement of individuals between populations
Results in gene flow Populations become homogeneous Reduced genetic variation between populations Fewer genetic differences between populations |
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Genetic Drift
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random change in allele frequencies from generation to generation
Impact of genetic drift depends on population size Greater effect in smaller populations |
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Population bottleneck
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is an extreme case of genetic drift
Occurs when a population falls to just a few individuals |
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Founder effect
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is another type of population bottleneck
Occurs when a few individuals colonize an area |
