Speciation and Time

Review What is evolution? What is natural selection?

Speciation Speciation is the process by which new species come into existence

What is a species? Species – organisms that are capable of breeding and produce fertile offspring

Are these the same species? Cat Dog

Are these the same species? Great Dane Golden retriever

Donkeys and horses can have offspring: Mules Mules are not fertile Thus they do not fit the definition of being the same species.

How are new species made? Populations must become reproductively isolated from one another for speciation to occur Reproductive isolation means that two populations are unable to mate together

If two populations stop mating with each other, natural selection can drive them to become different species

Geographic isolation Reproductive isolation due to geographic features Can be caused by formation of new rivers or mountains

Behavioral isolation Reproductive isolation due to different behaviors Birds have different songs and are only attracted to mates with the same song as them.

Reproductive isolation due to mating at different times Temporal isolation Reproductive isolation due to mating at different times Ex. Morning glories and moonflowers

Why is reproductive isolation needed for speciation? Review What is a species? Why is reproductive isolation needed for speciation? A population of rabbits is separated by a river that they cannot cross and stop breeding with each other. What kind of isolation is this?

Is there enough time for evolution? Speciation can take hundreds or thousands or years Is it possible for all of life to have evolved in that time period?

How old is the Earth?

4.54 Billion years

Evidence for an old Earth Half-Life radioactive dating: Measuring how old something is based upon how much radiation is left in it. Radioactive dating has placed the age of the world at approximately 4.54 billion years.

4 540 000 000 I have existed for less than 0.000000005% as long as the Earth The United States has existed for 0.00000005% as long as the Earth Humans have existed for 0.00045% as long as the Earth