Natural Selection & Adaption

Question 1

Nature of natural selection

Answer 1

1. Natural selection acts on phenotype, but evolution consists of changes in allele frequency
2. Natural selection acts on individuals, but its consequences occur in populations

The “unit of selection” debate: genes or individuals?

3. Natural selection is backward looking, not forward looking
4. Natural selection can produce new traits, even though it acts on existing traits
5. Natural selection acts on individuals not for the good of the groups

Altruisms and the group selection

6. Natural selection does cause adaption, but does not lead to perfection

-Constraints on evolution
- Many structures evolved from existing ones

7. Natural selection is nonrandom, but is not progressive

Question 2

Red-queen hypothesis

Answer 2

The response to selection does NOT improve the survivorship of a species

Question 3

Adaptation

Answer 3

A trait, or integrates suite of traits, that increases the fitness of its possessor and is called an adaptation and is said to be adaptive

1. It has a function
2. It results from natural selection and is fitness enhancing
3. It often implies problem (environmental change) and solution (adaption)

Question 4

Tests for adaptation

Answer 4

1. Engineering/ physiological test: structure must indeed function in the hypothesized sense
2. Heritability test
3. Fitness test: results of natural selection
4. Cause-effect test: the adaptive state must have evolved in the context of the hypothesized cause. Phylogenetic studies may help

Question 5

Not-adaptive traits

Answer 5

1. Necessary consequences of physics or chemistry
2. Random genetic drift, instead of natural selection
3. Correlated to an adaptive feature
4. Inherited trait, mot yet adapted to the recently changed environment
5. Exaptation

Question 6

Exaptation

Answer 6

A trait that evolved for other functions, or for not function at all, but which have been co-opted for a new use, is an exaptation

Question 7

Phenotypic Plasticity

Answer 7

The ability of an organism with a given genotype in response to change in the environment is called phenotypic plasticity

Question 8

Why are adaptations imperfect?

Answer 8

• Time lag
• Historical constraints
• Trade-off (e.g. life history, next week)
• Genetic constraints
• Developmental/Physiological/Functional constraints

Question 9

Time Lag

Answer 9

It takes time for natural selection to operate

A population may be responding to a new environment and has not yet reached the maximum average fitness for a particular trait

Question 10

Historical contingency

Answer 10

(Almost) Every adaptive trait evolves from something else