The African Origin Hypothesis What do the data tell us?

Transcription

1 The African Origin Hypothesis What do the data tell us?

2 Mitochondrial DNA and Human Evolution Cann, Stoneking and Wilson, Nature WOS citations

3 Mitochondrial DNA and Human Evolution Cann, Stoneking and Wilson, Nature WOS citations mtdna - high mutation rate, no recombination

4 Mitochondrial DNA and Human Evolution Cann, Stoneking and Wilson, Nature WOS citations!!!! mtdna - high mutation rate, no recombination 147 samples, 5 Regions 20 Africans (interestingly all from the U.S.) 34 Asians 46 Caucasians 21 Australians 26 Papua New Guinea

5 Mitochondrial DNA and Human Evolution Cann, Stoneking and Wilson, Nature WOS citations!!!! mtdna - high mutation rate, no recombination 147 samples, 5 Regions 20 Africans (interestingly all from the U.S.) 34 Asians 46 Caucasians 21 Australians 26 Papua New Guinea Restriction Mapping

6 133 distinct types Good support for geographical patterns.

7 Africans are the most diverse group.

8 Parsimony Analysis Tree is created based on the smallest number of changes.

9 Parsimony Analysis Tree is created based on the smallest number of changes. The simplest explanation is considered to be a correct representation of the evolutionary history.

10 Parsimony Analysis Tree is created based on the smallest number of changes. The simplest explanation is considered to be a correct representation of the evolutionary history. Problems: Multiple most parsimonious trees

11 Parsimony Analysis Tree is created based on the smallest number of changes. The simplest explanation is considered to be a correct representation of the evolutionary history. Problems: Multiple most parsimonious trees Sub-optimal trees might be correct

12 Parsimony Analysis Tree is created based on the smallest number of changes. The simplest explanation is considered to be a correct representation of the evolutionary history. Problems: Multiple most parsimonious trees Sub-optimal trees might be correct Long branch attraction

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15 Results Two primary branches one that is composed entirely of Africans, the other including all 5 of the populations studied. African origin because the two primary branches both lead to African mtdna s

16 Results Two primary branches one that is composed entirely of Africans, the other including all 5 of the populations studied. African origin because the two primary branches both lead to African mtdna s Each population stems from multiple lineages connected to the tree at widely dispersed positions. Each group was colonized multiple times

17 Last Common Ancestor Assume constant mutation rate Used Archeological evidence to get a time frame and estimated % divergence 2-4% / million years Last common ancestor was 62, ,000 years ago

18 Out of Africa Timeframe Used the oldest clusters of mtdna that don t not contain African types. 90, ,000 ya Agrees with fossil record evidence 100, ,000 ya

19 Major Criticisms Mid-point rooting method Assumes the rate of evolution has been the same in all lineages. If evolution were faster in African mtdna, then deep lineages would not reflect an African origin. Restriction analysis is an indirect method of comparing mtdna Small sample (AA were used to represent native Africans) No statistical justification for inferring African Origin Inadequate calibration rate of mtdna evolution Did not account for saturation

20 WOS Citations! Use chimp mtdna as an outgroup 2 hypervariable regions of mtdna - Sequence Data 189 individuals 121 native Africans (many locations) 20 Papua New Guinea 1 Australian 15 Europeans 24 Asians 8 African Americans

21 Results - Concordance with Cann et al Same branching pattern - deepest node shows two groups one of which is an all African clade the other is all of the other populations as well as other African clades. Two statistical tests- suggest African origin - these trees are significantly more parsimonious than other groups as the basal group. Accounted for substitutions and dates of most common recent ancestor not significantly different. As well as out of Africa timing.

22 Geographic Origin of Human mtdna: Phylogenetic Evidence from Control Region Sequences Maddison, Ruvolo, and Swofford, Sys Biol Ancestral State - Parsimony considers the entire tree structure and therefore clades beyond the basal clade must be examined to determine the most parsimonious state.

23 Maddison, Ruvolo, and Swofford Parsimony Analysis - Only conducted a single search and placed a limit of 100 trees, all of which only differed from each other by one or two changes. They probably did not get a diverse collection of shorter trees (trees that did not support a non- African hypothesis).

24 Maddison, Ruvolo, and Swofford Parsimony - Searched for trees that support a non-african hypothesis. Found a tree that only had one more mutation to support an Out of Papua New Guinea - hypothesis.

25 Outgroup - Is the Chimp Sequence Too Different? Highly Variable Region - Is the chimp sequence too divergent? Random number generator Found same rooting pattern.