Theories of Evolution

1) Lamarck French scientist Late 1700’s- early 1800’s “acquired traits” (use it or lose it) theory traits are not determined by genes but by “need” EX: giraffe necks grow longer because they stretch to reach the leaves higher up.

2) Charles Darwin English scientist Developed his theory of “natural selection” in the mid 1800’s Was a naturalist on the HMS Beagle (traveled around the world, mostly the southern hemisphere) for 5 years.

Voyage of the HMS Beagle

Darwin Noticed organisms had some similarities even when they lived far apart. * Darwin’s Finches Kept records & collected specimens Published “The Origin of Species…”

Darwin’s Finches

Darwin read other published works and was influenced by: 1) Lamarck’s Theory 2) Lyell’s book on Geology 3) Malthus’ book on human population & economics

Natural Selection Nature selects those that are best adapted to survive. “Survival of the Fittest” Adaptive advantage = a favorable trait

What is fitness? “Measure of a trait’s relative contribution to the following generation” Ability of a trait to lead to reproductive success…more babies = more “fit”.

Darwin’s Theory of Natural Selection has 4 principles Individuals in a population have differences The differences of individuals are inherited Organisms have more offspring than can survive Differences that increase reproductive success are more likely to stay in a population

Patterns of Evolution

1) Coevolution 2 species in close association evolving together. ( or a species evolving as a result of evolution in another species) These organisms may depend exclusively on each other & be highly specialized!

2) Convergent Evolution unrelated species becoming more similar over time. EX: Dolphin (mammal) and fish.

3) Divergent Evolution related species becoming more different over time.

Can be the result of: 1) artificial selection – humans selecting the traits and breeding for those traits (purebred dogs) 2) adaptive radiation – many species evolve from one species (Darwin’s finches)

The Peppered Moth – an example of how human’s can affect a species

Which colored moth has the advantage?

Genetic Equilibrium

What is genetic equilibrium? A balance of alleles within a population Genetic equilibrium does not exist!

5 reason genetic equilibrium does not exist… Mutations – random mutations alter genetic information Sometimes new traits can develop. Harmful traits are usually eliminated over time.

2) Migration Immigration – movement INTO a population Emigration – movement out of a population When individual organisms move in or out of a population their genes go with them!

3) Genetic Drift Changes in a population that are caused by chance or random events. EX: large volcano, fire, flood, disease Genetic drift will have more effect on a small population more than on a large population.

4) Non-random Mating Non-random mating would lead to less “selection” and all alleles would have an equal chance of being passed on. Some populations do have random mating, many animals do not.

5) Natural selection “Bad” traits are usually eliminated from a population as a result of natural selection.

3 ways natural selection affects populations & their traits 1) Stabilizing selection – the “middle” trait is the most favorable. There will be few organisms at the extremes.

2) Directional selection One of the “extreme” versions of a trait is the most favorable. Most individuals will have that trait.

3) Disruptive selection Both “extreme” traits are favorable, but the “middle” trait is not.

Hardy - Weinberg Shows genetic equilibrium p2 + pq + q2 = 1 (p = dominant allele, q = recessive allele)