Evolution: Fact and Theory  Fact: Species change over time.  Theory: Species arise from common descent through natural selection  Random mutations lead to changes in genes.  Changes in genes lead to changes in physical form (phenotype)  Physical form best adapted to the environment at the time produce more offspring and thus survive.  Evolution the theory addresses the origin of species NOT the origin of life.

Fossil Record: Evolutionary transition from Fish to Amphibians –1991 – A fish-like tetrapod (Acanthostega gunnari ) one specimen is so well preserved it has internal gills! –1998 – A Devonian fish is discovered in Pennsylvania eight fingers common to the earliest of tetrapods! –2004 –Tiktaalik roseae found in Canada has the thin, fish-like bones AND the tetrapod arm bones in the same structure!

Evolutionary transitions: Dinosaurs to birds

Evolutionary transitions: Horses Over 50 million years, horses adapted from woods to plains.

Evolutionary transitions: Elephants There have been 22 new species in the last 6 million years. 20 of them are extinct. In the last 4 million years there have been 10 successive species of Indian elephants alone. From J. Shoshani (1997) Natural History, 106, 38

Evolutionary transitions: Artiodactyls to Whales 29+ Intermediate forms

Evolutionary transitions: Humans Human and great ape fossil record leads to an estimate for the last common ancestor date as approximately 5-6 million years ago Note that this image only goes back approximately 1.2 million years and the upper left image is the modern chimpanzee for comparison Image: Smithsonian Institute

Genetic Evidence: Humans and Great Apes  Mutation Rates  Humans: 3.75 mutations per year  Chimps: 5 mutations per year  8.75 differences per year between the two populations  Genome sequences for the two species indicate a total of 40 million differences between the two genomes  Leads to a last common ancestor date of app. 5 million years ago  Note this is a crude estimate a (much) more careful analysis indicates a range of 5-6 million years ago  Kondrashov A. S. (2002) Direct Estimates of Human Per Nucleotide Mutation Rates at 20 Loci Causing Mendelain Diseases; Human Mutation 21-12:27  Nachman M. W., and Crowell S. L. (2000) Estimate of the Mutation Rate per Nucleotide in Humans; Genetics :304

Large scale Chromosome changes Genome sequencing of chimp and human chromosomes reveal that all 9 chromosome differences (white regions) –result from simple inversions (shown by arrows) –and one fusion. “A Spectacular confirmation” Figure from RELICS OF EDEN by Daniel J. Fairbanks, Prometheus Books, New York, 2007

Chromosome Numbers in the great apes (Hominidae): human (Homo)23 pairs chimpanzee (Pan)24 pairs gorilla (Gorilla)24 pairs orangutan (Pogo)24 pairs Testable prediction: Testable prediction: The marks of that fusion must appear in one of the human chromosomes. Centromere Telomere Ancestral Chromosomes Fusion Homo sapiens Centromere #1 Telomere sequences Centromere #2

“Chromosome 2 is unique to the human lineage of evolution, having emerged as a result of head-to- head fusion of two acrocentric chromosomes that remained separate in other primates. The precise fusion site has been located in 2q13–2q14.1 (ref. 2; hg 16: – ), where our analysis confirmed the presence of multiple subtelomeric duplications to chromosomes 1, 5, 8, 9, 10, 12, 19, 21 and 22 (Fig. 3; Supplementary Fig. 3a, region A). During the formation of human chromosome 2, one of the two centromeres became inactivated (2q21, which corresponds to the centromere from chimp chromosome 13) and the centromeric structure quickly deterioriated (42).” Homo sapiens centromere #13 (inactive) Telomere sequences Hillier et al (2005) “Generation and Annotation of the DNA sequences of human chromosomes 2 and 4,” Nature 434: Human Chromosome #2 shows the exact point at which this fusion took place centromere #12 (active)