Biological Evolution

What is Evolution

• Evolution is descent with modification

• Microevolution = changes in gene (allele) frequency in a population from one generation to the next

• Macroevolution = descent of different species from a common ancestor over many generations

Evolution Explained • NOT simply change over time

– Ex: Life cycle is NOT evolution

• MUST involve DESCENT through GENETIC INHERITANCE

• Change in a POPULATION over GENERATIONS of time

• Underlying Concepts:

–All organisms share a Common Ancestor

–Occurs through Natural Selection

Natural Selection 1. Variation in traits: more than one allele for a

trait; one allele may be more advantageous than another

2. Differential reproduction: NOT all individuals get to reproduce to their full potential

3. Heredity: adaptations are genetic

4. End result: more advantageous trait allows individuals to survive and produce more offspring

Natural Selection

Natural Selection

Natural Selection

Shift in Allele Frequency

• Mutations can produce new phenotypes that may or may not be beneficial to the organism

• If the new allele is beneficial, then those organisms will be more “fit” and therefore better able to reproduce.

• Over generations of time, this will cause the new allele to become more frequent in the population.

Fitness • Fitness = how good a particular genotype is at

leaving offspring in the next generation compared to other genotypes

• FITNESS is INHERITED! • Fitness will increase one or more of the following:

– Ability to Survive – Find a Mate – Produce Offspring

• Fitness is NOT necessarily strongest, fastest, or biggest.

• Ultimate Goal = transmit GENES to the next generation

Sexual Selection • Special case of natural selection

• Acts on an organism’s ability to obtain &/or successfully copulate with a mate

• Organisms may go to extreme lengths for sex

– Peacock tail

– Elephant seals fight

– Fruit flies dance

– Some even die for it! (male praying mantis)

Artificial Selection • Artificial Selection = people (NOT nature) select

which organisms get to reproduce

• Farmers and breeders commonly cultivate crops using Selective Breeding

Adaptation • Adaptation = inherited characteristic in a

population that increases fitness

• Adaptation Types

– Behavioral

– Biochemical

– Anatomical

• An adaptation is NOT ACQUIRED during an organism’s lifetime

Lamarck = Acquired Traits (wrong)

Darwin = Inherited Variation & Natural Selection (correct)

Giraffes needed longer necks so they “grew” longer necks through repeated use. THIS IS INCORRECT!

Giraffes that INHERITED longer necks were better able to survive, so they passed those genes on to their offspring.

Adaptation • Functional = Produced by Natural Selection

• Heritable = MUST be able to be INHERITED (genetic trait)

• Adaptive = increases the fitness of an organism

Speciation • Species is the biggest “gene pool” possible

under natural conditions.

• If the organisms can breed and produce fertile offspring, they are the same species. – German Sheppard + Chihuahua = puppy (fertile)

– Horse + Donkey = Mule (sterile hybrid)

– Horse & Donkey (NOT the same species)

• Speciation produces 2 or more separate species caused by: – Geographic Isolation

– Reproductive Isolation

Speciation of Fruit Flies

• A population of wild fruit flies lays eggs on rotting bananas…

• Disaster strikes: a hurricane washes the bananas and immature fruit flies out to sea. The bananas eventually wash up on the mainland. There are now 2 separate populations of fruit flies that cannot mate due to location.

• Populations become different due to slightly different conditions on the island. This causes a shift in allele frequency in the island population because of selection pressures.

• So we meet again: If another storm reintroduces the island fruit flies to the mainland fruit flies, they will not readily mate with each other due to differing courtship behaviors. The few that do mate produce inviable eggs because of genetic differences in the populations.

Misconceptions • Natural Selection does NOT

produce perfection.

• An organism cannot “adapt” during its lifetime. It cannot “try” to change. That is NOT adaptation. Adaptations MUST be GENETIC!

• Natural Selection is NOT random: variations that aid survival and reproduction are more likely to become common in the population

EVOLUTION

DOES NOT

WORK THIS WAY!!!

What I NEED is a GOOD FUR COAT!