3. Adaptions and Natural Selection

• nature chooses the designs that work best in any given circumstance and therefore shapes organisms to meet the challenges they face
• **reproduction!

favorable traits that accumulate over time

sex cells

carrying two copies of each gene

half of the chromosomes

alternative versions of a gene that can occur at the same locus

two alleles match at a locus

two alleles differ at a locus

by coding for proteins

• 1. phenotypic variation
• 2. genetic variation
• 3. environmental variation

all variation is due to environment. none of the differences are caused by genetic differences.

• cost - it must pay for itself in reproductive success
• variation - selection only chooses what already exists
• time - if environment changes too quickly, NS cant keep up.

• track environmental changes and adjust phenotype accordingly
• ex. pupil size

a particular pattern of response to environment

adaptions that resist environmental influence

occur when the facultative responses of an organism are overwhelmed

low, they are environmental responses.

• through the expression, through reaction norms.
• reaction norms can be highly variable

• gene 
• individual 
• group

a gene that increases the fitness of its average carrier will eventually spread.

a gene could spread if it caused its bearer to decrease their own fitness in order to increase the reproduction of other bearers of the same gene

back door to the next generation

• rb>c
• benefit to recipient X probability that recipient and altruist have the same gene > cost to altruist

= organisms reproductive success + organisms effect on reproduction of its relatives.

• 1. cost is low
• 2. benefit is large
• 3. high coefficient of relatedness (r)