The Modern Theory of Evolution

A. Evidence

1. The heart has a long history - 4.6 billion years

a. Radioactive decay - good - ancient rocks

b. Kelvin's problem - killed evolution for a time

2. The fossil Record

a. Shows succession of living things

b. Simpler forms precede more complex

c. One can make a sequence showing evolution of some animals

1. Horses

2. Humans

3. Living members of groups of organisms show similar structure

a. Fore-limbs of vertebrates

1. Homologous parts

b. The real unity of life is seen in the DNA story - all organisms follow the same genetic code

4. Adaptedness o living things

a. Organisms it the environment very closely

b. Adaptations take place over a long period of time

c. Very small changes are taking place even now

B. Lets look at how evolution works

1. Mutations

a. Mutations occur at random - they are a mistake in the DNA strand

b. Caused by:

1. Radiation - cosmic rays

2. Mutagenic chemicals

c. The mutation rate is slow but steady

d. Mutation is the source of variability in organisms

e. Most mutations are bad

1. Only a few mutations benefit organisms

f. Mutations are stored in the genome of an organism

1. Alleles of Mendel are really mutations that have been stored

g. Classical Mendelian genetics shows how mutations are exposed by segregation of alleles

1. The Mendelian genetics system preserves and exposes mutations to selection

2. Selection

a. If a particular mutation is good it allows its holder to produce more offspring

1. We say that a beneficial mutation increases the fitness of the organism

2. Fitness is only a comparison between genotypes on the basis of reproductive success

b. Those individuals with good alleles reproduce better and leave more copies of the allele

1. Eventually the allele will spread through the population

c. I there is not selection allele frequency won't change

1. This is the result of simple mathematics

d. Selection by nature is an exact analogue of selection by humans

1. Dog breeds

2. Tropical Fish

3. Corn

e. Humans select the traits that are most successful - nature selects traits which fit the environment