remainders of human bio evolution

natural selection

the process by which a species becomes better adapted to its env’t. those w/favourable traits have a survival advantage and pass those characteristics onto subsequent gens

selection pressure

a factor that influences the survival of an individual w/in a pop

darwin’s observations in natural selection

1. Variation: all members of a species vary. these variations were passed on from one gene to the next, w/ characteristics displayed by the parents being passed on to their offspring.

2. Birth rate: all living organisms reproduce at a rate far greater than that at which their food supply + other resources inc. This would normally result in overcrowding.

3. Nature’s balance: although the birth rate of organisms was very high, each species’ numbers tended to remain at a relatively constant level.

darwin’s interpretation/principles to natural selection

1. due to high birth rate + limited resources, there must be a struggle for existence

2. those organisms w/characteristics best suited to their env’t are more likely to survive

3. survival of the fittest is possible bc there is variation w/in a species

4. those organisms that survive will pass on favourable characteristics to other organisms

5. the alleles that produce favourable traits gradually inc in gene pool

gene flow

the transfer of alleles from 1 pop to another through migration

migration

the movement of people from 1 area to another w/the intention of settling permanently

geographical barrier to gene flow

a feature of the landscape that prevents pops from interbreeding e.g ocean

sociocultural barrier to gene flow

a barrier to interbreeding that is due to social or cultural factors e.g economic status

genetic drift

the random, non directional change in allele frequency between gens

example of genetic drift

• isolated Aboriginal pops on Bentinck + Mornington islands

• islands were once part of mainland, but isolated due to rising sea levels

• mornington remained some contact w/main due to stepping stone islands

• when comparing blood groups, mornington had low B allele, high A allele

• bentinck had high B allele, low A allele

founder effect

an extreme example of genetic drift when a small group moves away from its homeland to a totally new area + establishes a new pop

example of founder effect

• isolated group in Pennsylvania called Dunkers descended from Old German Baptist Brethren

• Migrated to US in 18th century

• maintained religious practises such as only marrying in group

• research studied traits between Dunkers + germans such as handedness, blood groups

• Dunkers showed diff alleles freqs to present day pop + surrounding american pop

speciation

the process of new species developing

principal 1 to speciation - variation

A range of variations exists within the pop, which shares a common gene pool

principle 2 to speciation - isolation

A barrier has formed, dividing the pop into two. No interbreeding occurs between the two pops. Each pop has a separate gene pool.

principle 3 to speciation - selection

Diff selection pressures act on each of the two pops over a number of gens. This brings about a change in the gene freqs of each gene pool. Such changes lead to the evolution of separate subspecies.

principle 4 to speciation - speciation

Over a long period of time the changes in the gene freqs may be great enough to prevent the production of fertile offspring by interbreeding between the two pops from ever occurring again. When this happens, two species exist.