Biology Chapter 15 Notes
Nature Selection and the Evidence for Evolution
English Scientist Charles Darwin (1809-1882)
 Developed the theory of evolution by natural selection
 Natural Selection is a mechanism for change in population-survival of the fittest
 Two types of Adaptations
 Behavioral
 Structural
 Mimicry-resemble another species that is harmful
 Camouflage-a species being able to blend into its environment
 Anatomy
o Homologous structures-Structural features with a common
evolutionary origin
 Ex. Whale forelimb, Crocodile forelimb, and a bird wingbones are modified according to its function
o Analogous structures-The body parts of organisms don’t have a
common evolutionary origin but a similar function
 Ex. Insect and bird wings are similar in function but not
in structure
o Vestigial structures- A present day body feature that no longer
serves its original purpose, but was probably useful to previous
generations
 The eyes in blind mole-rats and cave fish
Embryology-The study of the development of embryos
 An embryo is the earliest stage of growth and development of both plant and animal organisms
Biochemistry-The science that deals with biological and chemical processes in organisms
 It provides strong evidence for evolution
Physical and well as environmental factors aid in the process of evolution
Mechanism of Evolution
Terms:
1.
2.
3.
4.
Gene pool- all the alleles possible in an organism
Allelic frequency-The percentage of any specific allele in the gene pool
Genetic equilibrium- A population having the same frequency of alleles over generations
Stabilizing selection- is natural selection that favors average individuals in a given population
and reduces variation in a population
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5. Directional selection-occurs when natural selection favors one of the extreme variations of a
trait and can lead to the rapid evolution of a population
6. Disruptive selection-Individuals with the extreme variation that results eventually in no
intermediate forms of the trait and leading to the evolution of two new species
7. Speciation- The evolution of new species, occurring when members of similar populations no
longer interbreed to produce fertile offspring within their natural environment.
Physical barriers can prevent interbreeding
8. Geographic isolation-occurs whenever a physical barrier divides a population-like the splitting of
Pangaea caused land animals to become separated
9. Reproductive isolation-occurs when formerly interbreeding organisms can no longer mate and
produce fertile offspring (Two types)
 Genetic material of the populations becomes so different that fertilization can’t
occur
 Behavioral- two different species won’t mate together so isolation occurs
10. Polyploid-Any individual or species with a multiple of the normal set of chromosomes
 Speciation rates of polyploids usually take only one generation but other
mechanisms occur slowly
a.) Gradualism is the idea that species originate through a gradual change in
adaptations
b.) In 1972, Niles Eldredge and Stephen J. Could proposed punctuated
equilibrium-states that speciation occurs relatively quickly, in rapid bursts,
with long periods of genetic equilibrium in between
Patterns of Evolution
11. Adaptive radiation- The result of an ancestral species evolving into an array of species to fit a
number of diverse habitats
12. Convergent evolution-occurs when distantly related species evolve to look alike
13. Divergent evolution-occurs when closely related species have evolved to look differently
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