Chap 16/17: Evolution Need to Know
Theory of Evolution
Darwin developed a scientific theory of biological evolution that explains how modern organisms
evolved over long periods of time through descent from common ancestors.
* a change in the frequency of alleles in a population over time.
Evidence of evolution:
Patterns in the distribution of living and fossil
species tell us how modern organisms evolved from
their ancestors.
homologous structures: adapted to different purposes
as the result of descent with modification from a
common ancestor.
universal genetic code (DNA) provides evidence of common descent.
Vestigial structures: inherited from ancestors but have lost most or all of original function
Embryological
The Grants have documented that natural selection takes place in wild Galápagos finch
populations frequently, and sometimes rapidly, and that variation within a species increases the
likelihood of the species adapting to and surviving environmental change.
Charles Darwin- main contributor to theory of evolution, author of On the Origin of Species
Fitness: the physical traits & behaviors that enable organisms to survive & reproduce in their
environment
Analogous functions: share common function not structure
Common descent: all species have shared or common ancestors
Adaptation: fitness arises through this process. This helps organisms become better suited to their
environment. Ex. Giraffe
Natural selection: the process by which those having traits that better enable them to adapt to
specific environmental pressures will tend to survive and reproduce
occurs in any situation in which more individuals are born than can survive, there is natural
heritable variation, and there is variable fitness among individuals..
Single gene traits: acts directly on phenotypes
Polygenic traits: affects the relative fitness of phenotypes producing types of selection
Directional: sift toward one end of the curve
Stabilizing: individuals at center have higher fitness
Disruptive: individuals at outer ends have higher fitness
Artificial selection: nature provides the variations, and humans select those they find useful.
Homologous structures: adapted to different purposes as a result of descent with modification
from common ancestor-similarities in embryonic development.
Analogous structures: common structure not common function
Vestigial: inherited from ancestor; lost original function
Gene pool: all the genes in a population
Gene frequency- the number of times an allele occurs in a gene pool
Reproductive Isolating Mechanisms: 2 populations can no longer breed
Reproductive: behavioral, geographic, temporal, mechanical
Genetic Variation: Three sources of genetic variation are mutation, genetic recombination during
sexual reproduction, and lateral gene transfer.
Genetic Drift: the change in the frequency of an allele in a population due to random
sampling of organisms
Bottleneck: occurs when a population's size is reduced usually from a disaster,
genetic variability is lost
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.
The Hardy-Weinberg principle : five conditions can disturb genetic equilibrium and cause
evolution to occur: (1) nonrandom mating; (2) small population size; and (3) immigration or
emigration; (4) mutations; or (5) natural selection.
P2 + 2pq + q2
p + q = 1 p2 = homozygous dominant alleles
q2= homozygous recessive alleles
2pq = heterozygous alleles
Reproductively isolated populations can evolve into two separate species.
behavioral isolation
geographic
temporal
A molecular clock uses mutation rates in DNA to estimate the time that two species have
been evolving independently.
Cladogram: diagram that depicts evolutionary relationships among groups. It is based
on phylogeny, (study of evolutionary relationships)-common ancestor
Convergent evolution: When unrelated organisms evolve similarities when adapting to similar
environments
Divergent evolution: When a species diverges over time into two different species, resulting in a
species becoming less like the original one
- Live in different ways than the common ancestor
- Caused by migration or nearby extinction of a nearby environment
- Prime example are the dinosaurs