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Lecture 18

Biology 1001A Lecture 18: Lecture 18 - Life on Earth, Bio 1001A

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Western University
Biology 1001A
Scott Mac Dougall- Shackleton

Lecture 18- Life on Earth Nov. 17, 2016 Clicker Questions: Outcomes Most recent common ancestor (MRCA) for a given group(s), given a phylogenetic tree. - Common ancestry was the main point in Darwin’s Origins. All cellular life has the same genetic code and can be traced back to find that there is a point at which we all shared a common ancestor (bacteria, archaea, eukarya). This is called LUCA- last universal common ancestor for a group of organisms - How long ago was it that the MRCA existed for those groups? With any combination of species on Earth. This shows the degree of relatedness (eg. humans and bacteria are not closely related as you have to go back far for the MRCA). - Branching points on the tree called “rendezvous” points. Why the idea that “humans are descended from chimps” is inaccurate. - If we are descended from chimps, why do they still exist on Earth? Our most recent common ancestor was not human but not chimp either. Why some traditional groupings of organisms (“reptiles”, “fish”) do not reflect evolutionary relationships - The Old world monkeys are more closely related to us than to New World monkeys! Therefore, the group “monkeys” does not represent evolutionary relationships. Class Notes: - ~18000 new species of life discovered each year. Discoveries can be of animals we have never seen before, those we have seen but just recently genetically identified as different from their relative species, or bones of species who have gone extinct. - 1.1-1.2 million species we have named…. About ~8.7 million eukaryotes predicted to exist on Earth. We have only named/ described up to 10%. Pedigree Collapse - Doing the math, every generation should double your relatives. So 30 generations back will have 2^30 relatives. But that many people didn’t exist back in that generation?! - If we go back far enough, any two individuals will have a common ancestor. Rendezvous Zero: Humans Themselves - The MCRA of all humans Lecture 18- Life on Earth Nov. 17, 2016 - How long ago was that? Using mathematical modelling, estimated to be about 3000 years ago/ 150 generations. Rendezvous One: Chimps and Bonobos - Our evolutionary cousins - Closest relatives - MCRA 6 million years
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