LESSON 2 – MECHANISMS OF EVOLUTION• Evolution – change in allele frequencies over

time. • Natural selection – the process by which

certain individuals are more likely to survive and reproduce, leading to changes in the alleles of a population or species.

• Alleles for traits that give an advantage in survival and reproduction are more likely to be passed on to offspring.

• Classic Example• Peppered moths in the United Kingdom• They were grey with black speckles in 1800s• This helped to camouflage the moths against the

lichen-covered trees of the moth’s environment, helping to avoid predators.

• The Industrial Revolution – coal burning released soot that settles on trees

• Then black-colored peppered moth were observed.• Moths that were black were more likely to survive

then reproduce then more in the population increased.

• ALLELE FREQUENCY• How common an allele occurs in a population.

An allele with a higher frequency is more common than one with a lower frequency.

• NATURAL SELECTION PRINCIPLES:1. Organisms produce more offspring than their

environments can support.2. Offspring vary in phenotype.3. Variation is caused by differences in alleles

inherited.4. The inheritance of alleles determines how likely

an individual organism is to survive and reproduce.

5. Only “helpful” alleles will be passed on to future offspring.

• MECHANISMS OF EVOLUTION• Population – group of organisms of the same

species that share a geographical area and breed with each other.

• Genetic drift – changes in allele frequencies that are due to chance events. – Migration – movement of individuals into or out

of a population.– Founder effect – formation of a new population

from just a few individuals who leave a larger population.

– Population bottleneck – when an entire population is reduced to just a few individuals, often as a result of some form of disaster such as disease.

• Speciation – formation of new, genetically distinct species from populations of existing species.

• Geographical isolation – divides two populations through a physical barrier, such as a canyon, river, or highway.

• Reproductive isolation – prevents this population from mating with members of the original population.

• Species – a group of organisms that can mate and produce fertile offspring.

• Isolating mechanisms – physical or behavioral trait that prevents a member of one species from mating with a member of a different species and producing fertile offspring.

• https://www.youtube.com/watch?v=aTftyFboC_M&list=PLT_3xjjmTinZcgruya5D1B5XLrB3sRSml&index=3