BSCI 106 Dr. Via

Spring 2000

Lecture 2. The Process of Evolution: How Adaptations Arise

1. Explanation: Supernatural forces or the result of natural laws?

a. Fundamental premise of all science: phenomena on earth are caused by processes resulting from natural earthly laws

b. Natural laws in biology in the context of laws of physics and chemistry

c. How do we discover natural laws?

2. The Theory of Evolution by Natural Selection: what is it??

a. Review of scientific method

b. Observation: change over time

c. Observation: descent with modification

d. Hypothesis: natural selection determines the direction of modification and thus leads to adaptation

3. Evolution as Fact and Theory

a. Fact = something that can be observed (i.e., change over time, descent with modification

b. Theory = "statement of what are held to be the natural laws, principles or causes of something that is known or observed" (Oxford English Dictionary).

c. The theory of evolution by natural selection is a statement of the mechanisms that produce change over time and descent with modification.

d. This is a theory like th eTheory of Gravitation, which explains why objects are pulled toward the center of the earth.

e. Change over time and descent with modification leads to adaptation. Thus, the evolutionary process that has produced this diversity unties all of biology!!

f. "Nothing in biology makes sense except in the light of evolution", Th. Dobzhansky, 1937

4. The four components of evolution by natural selection

a. Reproductive excess

b. Variation in characters that affect survival and reproduction

c. Some variants leave more offspring (natural selection)

d. Adaptive variation is inherited (genetically based variation in the phenotype)

e. RESULT: average characteristics of population changes (evolves)

to be more like the successful variants. THIS IS ADAPTIVE EVOLUTION!

f. If a-d are true, evolution is inevitable!

5. Evolution before Darwin

a. Aristotle and Scalae Naturae. 2000 years of belief in permanent and never changing forms.

b. Special Creation- each organism individually created by a supernatural being (but scientists seek natural, not supernatural explanations)

c. Linneaus (mid 1700's) documented diversity, still believed in fixity

e. challenges to static view

i. increased exploration by naturalists-- huge diversity and slight variations

ii. geology-- rocks come in layers, fossils

iii. change over time in fossil forms

iv. some fossilized organisms no longer found

f. How could change over time occur in only 4000 years?

i. catastrophism plus new creations?

g. Geologists Hutton and Lyell realized that current forces like wind, water, earthquakes and volcanos could explain all observations

h. For these slow processes to have shaped world, earth much older than 4000 yrs

6. Darwin's role

a. An unlikely intellectual revolutionary?

b. A persistent naturalist-- bothered by inconsistencies

c. "Take chances, make mistakes, get dirty!" (Ms. Frizzle, Magic School Bus); "combine fields" (Via, personal opinion). DARWIN DID!

7. Darwin's observations

a. Diversity in South America - species not permanent?

b. Snake with rudimentary hind limbs, penguins use wings to swim, snake with vibrating tail, but no rattle - makeshift?

c. On Galapagos, prickly pears differ on islands with and w/o tortoises, slightly varying forms of many species on different islands

d. domesticated varieties-- great changes in short period of time

8. Other relevant information

a. Economics-- Malthus notes that more individuals are produced than can survive

b. Geology-- Hutton and Lyell and age of earth

9. Darwin and Wallace's hypothesis (great minds think alike!)

a. Individuals differ in various characteristics

b. Survival and reproduction appears to depend on the characters that vary, so that individuals with particular characteristics are more successful

c. Wallace: "Those which, year by year, survived this terrible destruction must be, one the whole, whose which have some little superiority enabling them to escape each special form of death to which the great majority succumbed"

d. Darwin: "It at once struck me that under these circumstances favorable variations would tend to be preserved and unfavorable ones destroyed".

e. In Origin of Species; "Let us take the case of a wolf, which preys on various animals, securing [them] by . . . fleetness . . . The swiftest and slimmest wolves would have the best chance of surviving, and so be preserved or selected . . . now if any slight innate change of habit or structure benefited an individual wolf, it would have the best chance of surviving and leaving offspring. Some of its young would probably inherit the same habits or structures, and by the repetition of the process, a new variety might be formed".

NEXT TIME: Evidence for evolution: Predictions and observations to test the hypothesis that natural selection has produced adaptation..