EVOLUTION AND NATURAL SELECTION

textbook notes chapter 9.3

evolution

the change in characteristics of species over time (over generations)

phenotype

the observable characteristics/physical traits of an organism

genotype

the combination of alleles for a gene

population

a group of organisms of the same species living in a particular place at a particular time

gene pool

sum of all alleles in a given population

allele frequencies

how often each allele of a gene occurs in the gene pool for that population

Darwin’s 3 observations

1. variation

2. birth rate

3. natures balance

natural selection

• the process by which a species becomes better adapted to its environment

• individuals with favourable characteristics have a survival advantage and pass this onto subsequent generations

variation (darwins observations)

• all populations have variation and these variations will be passed on from generation to the next, with characteristics by the parents being passed on to their offspring

birth rate (darwins observations)

• all living organisms reproduce at a faster rate than which their food sources/ other resources increase

• this would normally result in overcrowding

nature’s balance (darwin’s observations)

although the birth rates of organisms were very high, each species number tended to remain at a relatively constant level

struggle for existence

the number of organisms is greater than the resources in the environment can support; therefore, there is competition between the organisms for the resources

survival of the fittest

those with characteristics best suited to their environment are more likely to survive but organisms with unfavourable characteristics die before they have a chance to reproduce

selective agent

environmental factor acting on the population

principles of evolution (how to structure response)

1. there is variation within a species (describe variation)

2. more offspring of a species are produced than can possibly survive to maturity

3. because of excessive birth rate and limited resources, there is a struggle for existence

4. individuals with characteristics best suited to the environment have more chance of surviving and reproducing (survival of the fittest)

5. favourable characteristics are passed onto the offspring

6. this therefore increases allele frequency