Section 5.6 Speciation and Evolution Chapter 5 Section 5.6 Speciation and Evolution

Speciation Speciation – the formation of a new species. Most species are believed to arise by a 3 step process called allopatric speciation. Allopatric speciation – the formation of a new species by reproductive isolation.

3 Steps of Allopatric Speciation A physical barrier separates a single interbreeding population into two or more groups that are isolated from each other. Natural selection works on the separated groups independently, so they evolve differently. In time, physical and/or behavioral differences between the two populations will become so pronounced that they would no longer be able to interbreed.

Examples of Physical Barriers Mountain ranges Oceans River Channels Canyons Islands

The Rate of Evolution 2 theories exist that attempt to explain the rate or speed of evolution: Theory of gradualism – the idea that speciation takes place slowly at a constant rate. Theory of punctuated equilibrium – the idea that species evolve rapidly, followed by a period of little to no change.

Divergent Evolution Another key term in evolution is divergent evolution. Divergent evolution is the evolution into many different species. Ex. Darwin’s Finches