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C O U R S E 
Human Evolution: Past and Future
John Hawks, University of Wisconsin
C O U R S E   L E C T U R E 
The Molecular Clock
Notes taken on February 10, 2014 by Edward Tanguay
phylogeny [figh-LAH-jin-nee]
understanding of the relationship between species
the relationship between species is a fundamental aspect of how evolution happened
when we add genetics to phylogeny, it gets complicated and involves math
how we use phylogeny to understand when certain species shared common ancestors with each other
humans, chimpanzees, gorillas, orangutans
four species of living homenoids
not a part of the group that includes the other homenoids
cladogram shows clades, or branches of an ancestral tree
today we use cladograms to understand the study of biology
allows you to understand the relationships between organism
genetics by and large reflect the phylogeny of the groups
humans are most genetically similar to chimpanzees
humans and chimps are next most genetically similar to gorillas
we're more distantly related in genetics to macaques
1962 Linus Pauling and student Emil Zuckerkandl
researched which amino acids there were in a protein hemoglobin in different kinds of organisms
seemed to show that the number of differences in the amino acid sequences seemed to reflect the time that those organisms shared a common ancestor according to the fossil record
e.g. humans and apes are 1 amino acid different, yet humans and horses are 17 amino acids different
proposed the theory "the molecular clock"
differences in amino acids in hemoglobin are accumulating at a regular rate over time
if this were true, we could determine how long two species shared a common ancestor as a separate way than using the fossil record
i.e. we could look at how different they are and determine that they shared a common ancestor beginning at a certain time in the past
1992: research, Wendy Bailey
studying a part of the DNA called the psi-eta-globin
a part of the genome which is near the betaglobin gene which is part of hemoglobin
in some ancient organisms psi-eta-globin may have been functional but in all living primates, it has lost its function, it doesn't make any product anymore
why would something that has no function exist and persist in primate genomes?
our genomes are full of genes that once worked in ancient organisms but stopped working at some point in our evolutionary history
some primates share a deactivation of the gene that creates vitamin C, some animals have no problem creating vitamin C, but primates have to get vitamin C from external sources
e.g. GULOP which still exists in the human genome
the further we move away from humans into other primates, the higher the difference of the gene sequence for psi-eta-globin
the percentage differences between the genes allows us to put age estimates on when the branchings occurred
e.g. humans and macaques in terms of their DNA are about twice as different than humans and orangatans are
this is what is referred to as the molecular clock
molecular clock is an assumption that genes change at a constant rate but there may be mutations which cause them to converge on each other
to estimate times from these percentages, you have to know how often genetic changes happen, to further increase accuracy, you have to root this to the fossil record
e.g. Sivapithecus [shee-vah-PITH-i-kuss] is a genus of extinct primates that may have been the ancestor to modern orangutans, fossil record indicates that it lived about 12 million years ago