1 Biological Species Concept “Species are groups of interbreeding natural populations that are reproductively isolated from other such groups” reproductive isolation: genetic differences preventing successful interbreeding - Ernst Mayr, 1940

2 Species on Earth # species on Earth today: ~3-50 million # of species that ever lived: ~ million It has been estimated that ~99% of all species that have ever lived are extinct

3 Speciation –the process by which one species splits into two or more species How? –Subgroups of the species become reproductively isolated Classes of reproductive isolation –Prezygotic: prevents zygote formation –Postzygotic: prevents survival or reproduction of offspring

4 Classes of speciation Allopatric –geographic separation Parapatric –divergence across a continous habitat Sympatric –No separation

“Female Fickleness May Split a Species” Source: Matt Kaplan, ScienceNOW Daily News, 11/30/2007 NY females prefer males with bright yellow bibs WI females prefer males with large black masks When mixed, preferences stayed the same 5

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7 Transitional fossils Fossils of organisms with morphological features intermediate between those of an ancestral species and its descendants ?

8 Fish to tetropods Tiktaalik Discovered in 2004 on Ellesmere Island, Canada million years ago

9 Dinosaurs to Birds Archaeopteryx 150 Million years ago

10 Land mammals to sea mammals Source: evolution.berkeley.edu

11 Fossil DNA Remnants in a present-day genome of previously functional DNA that “eroded” due to an accumulation of mutations …CAATGACGTTAGCATGAG… …GAATGGCGTAAGCCTGAG… ancient DNA present-day DNA

12 Human chromosome 2: A fusion Human chromosome 2 Chimp chromosomes 2q and 2p Remnants of old telomeresRemnants of old centromere