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

Species on Earth # species on Earth today: ~3-50 million # of species that ever lived: ~75-2500 million It has been estimated that ~99% of all species that have ever lived are extinct

Speciation Speciation How? Classes of reproductive isolation 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

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

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

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

Fish to tetropods Tiktaalik Discovered in 2004 on Ellesmere Island, Canada. 385-359 million years ago

Dinosaurs to Birds 150 Million years ago Archaeopteryx

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

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

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