Evolution Notes
Chapters 15
I.
II.
III.
IV.
V.
VI.
Voyage of the Beagle
a. Beagle (ship) sailed from England, to South America, the Galapagos Islands, New Zealand, Australia, and the tip of
Africa.
b. During his time on ship he made many observations about native organisms.
Darwin’s Theory of Natural Selection: Five postulates
a. Over production
i. Organisms produce many more offspring than will survive
b. Struggle for existence
i. Organisms compete for a limited amount of resources
c. Variations
i. Differences in physical traits can show up in organisms of the same species. These variations are a result
of genetic mutation. These changes can be passed on to the next generation.
1. Artificial selection- nature provided variation is selected by humans for its usefulness.
d. Survival of the Fittest
i. Organisms with traits that give them an advantage in the competition will survive and therefore pass
these traits onto the next generation.
1. Fitness- ability to survive and reproduce
2. Natural selection- fitness. Like artificial selection, except nature chooses the traits.
e. Origin of new species (Descent with Modification)
i. Over many generations these accumulated inherited
traits will give rise to new species.
1. Gradualism- evolution generally occurs
uniformly and by the steady and gradual
transformation of whole lineages
2. Punctuated Equilibrium- organisms
experience little change for most of their
geological history, and then when evolution
does occur, it is localized in rare, rapid events
of branching speciation
Other Scientists
a. Hutton- the Earth was formed slowly by already known
processes
b. Lyell- the processes that shaped the Earth are still going on today
c. Lamarck- by use or disuse, organisms can acquire or lose certain traits during their lifetime. These traits could then
be passed on to their offspring. Overtime, this leads to change in a species.
d. Malthus- without things like war, famine, and disease the human population would grow unchecked until we ran
out of space, food, and water.
e. Alfred Wallace- had the same ideas as Darwin at the same time, never got the credit for it.
What is Evolution?
a. Evolution- change over time! The process by which modern organisms have descended from ancient organisms.
Direct Evidence of Evolution
a. Aside from actually living through an evolutionary change the only other DIRECT evidence we have is the fossil
record. Fossils – Directly link us to what used to be present on the earth.
Indirect Evidence of Evolution
a. Things we can see today that might indicate some common ancestry among organisms.
i. Embryological development
ii. Biochemical similarities
1. DNA structure
2. Protein structure
b. Homologous- structures which are similar in composition even though they may function differently.
c. Analogous structures- functions are similar but structures are different.
d. Vestigial structures- structures that are not used, but left over in an organism from an ancestor.
Chapter 16
I.
II.
III.
IV.
V.
VI.
Variation and Gene Pools
a. Gene pool- all the genes, including the different alleles that are in a population.
b. Relative frequency of alleles is the number of times that the allele occurs in the gene pool compare to how often
the other alleles occur.
c. In genetic terms, evolution is a change in the relative frequency of alleles in a population.
Sources of Genetic Variation
a. Mutations
b. Gene Shuffling
Single-gene and Polygenic Traits
a. Single-gene trait- controlled by a single gene with two alleles.
i. Natural selection on single-gene traits leads to changes in allele frequencies.
b. Polygenic trait- controlled by two or more genes. Each gene often has multiple alleles. As a result, one polygenic
trait can have many possible phenotypes.
i. Since there are more phenotype in polygenic traits, natural selection affects these traits differently.
1.
Directional Selection- individuals at one
end of the curve have higher fitness than
individuals in the middle or at the other
end.
2.
Stabilizing Selection- individuals near the
center of a curve have higher fitness than
the individuals at either end.
3.
Disruptive Selection- Individuals at the
upper and lower ends of the curve have
higher fitness than individuals near the
middle.
Speciation- Creation of new species.
a. As new species evolve, populations become reproductively isolated from one another. Once two populations
cannot interbreed and produce fertile offspring new species form.
Agents of Speciation (What causes change over time!)
a. Isolating mechanisms
i. Behavioral- two populations are capable of interbreeding but have different courtship rituals
ii. Geographic- populations are separated by geographic barriers such as rivers, mountains, bodies of water
iii. Temporal- two populations reproduce a different times
b. Mutations (such as point, frame shift, inversion, deletion, substitution, duplications)
c. Genetic Drift- changes in allele frequencies of a gene pool
i. Founder Effect- a few organisms with only a fraction of the alleles found in their original gene pool
inhabit an area.
ii. Bottle Neck- when near extinction due to natural disaster or human influence, a majority of the organisms
will not reproduce and a very limited number of organisms will contribute to the gene pool
d. Gene Flow- movement of alleles between two populations. New alleles can be due to migrating organisms. This
can keep two close populations gene pools similar.
e. Nonrandom Mating- organisms mating by closeness of geno/phenotypes. Like in inbreeding.
f. Natural Selection- populations adapt to their environment.
Evolution versus Genetic Equilibrium
a. When allele frequencies remain the same genetic equilibrium occurs. Five conditions must be present to have
genetic equilibrium:
i. Random Mating
iv. No Movement Into or Out of the
ii. Large Population
Population
iii. No Mutations
v. No Natural Selection