18:49,1,Molecular Evolution,18:49,2 /83,Outline,Evolutionary Tree Reconstruction “Out of Africa” hypothesis Did we evolve from Neanderthals? Distance Based Phylogeny Neighbor Joining Algorithm Additive Phylogeny Least Squares Distance Phylogeny UPGMA,18:49,3 /83,Evolutionary Tree Reconstruction,18:49,4 /83,Early Evolutionary Studies,Anatomical features were the dominant criteria used to derive evolutionary relationships between species since Darwin till early 1960sThe evolutionary relationships derived from these relatively subjective observations were often inconclusive. Some of them were later proved incorrect,18:49,5 /83,Evolutionary Trees: DNA-based Approach,1960s: Emile Zuckerkandl and Linus Pauling brought reconstructing evolutionary relationships with DNA into the spotlight In the first few years after Zuckerkandl and Pauling proposed using DNA for evolutionary studies, the possibility of reconstructing evolutionary trees by DNA analysis was hotly debated Now it is a dominant approach to study evolution.,18:49,6 /83,Emile Zuckerkandl on human-gorilla evolutionary relationships:,From the point of hemoglobin（血红蛋白） structure, it appears that gorilla is just an abnormal human, or man an abnormal gorilla, and the two species form actually one continuous population. Emile Zuckerkandl, Classification and Human Evolution, 1963,18:49,7 /83,Gaylord Simpson vs. Emile Zuckerkandl:,From the point of hemoglobin structure, it appears that gorilla is just an abnormal human, or man an abnormal gorilla, and the two species form actually one continuous population. Emile Zuckerkandl, Classification and Human Evolution, 1963,From any point of view other than that properly specified, that is of course nonsense. What the comparison really indicate is that hemoglobin is a bad choice and has nothing to tell us about attributes, or indeed tells us a lie. Gaylord Simpson, Science, 1964,18:49,8 /83,18:49,9 /83,Who are closer?,18:49,10 /83,Human-Chimpanzee Split?,18:49,11 /83,Chimpanzee-Gorilla Split?,18:49,12 /83,Three-way Split?,18:49,13 /83,Evolution and DNA Analysis: the Giant Panda（大熊猫） Riddle,For roughly 100 years scientists were unable to figure out which family the giant panda belongs toGiant pandas look like bears but have features that are unusual for bears and typical for raccoons（浣熊）, e.g., they do not hibernateIn 1985, Steven OBrien and colleagues solved the giant panda classification problem using DNA sequences and algorithms,18:49,14 /83,Evolutionary Tree of Bears and Raccoons,棕熊,北极熊,黑熊,眼镜熊,大熊猫,浣熊,小熊猫,18:49,15 /83,Out of Africa Hypothesis,Around the time the giant panda riddle was solved, a DNA-based reconstruction of the human evolutionary tree led to the Out of Africa Hypothesis that claims our most ancient ancestor lived in Africa roughly 200,000 years ago。,18:49,16 /83,http:/www.mun.ca/biology/scarr/Out_of_Africa.html,18:49,17 /83,Mitochondrial genome variation and the origin of modern humans,18:49,18 /83,The Origin of Humans: ”Out of Africa” vs Multiregional Hypothesis,Out of Africa: Humans evolved in Africa 150,000 years ago Humans migrated out of Africa, replacing other shumanoids around the globe There is no direct descendence from Neanderthals,Multiregional: Humans evolved in the last two million years as a single species. Independent appearance of modern traits in different areas Humans migrated out of Africa mixing with other humanoids on the way There is a genetic continuity from Neanderthals to humans,18:49,19 /83,mtDNA analysis supports “Out of Africa” Hypothesis,African origin of humans inferred from: African population was the most diverse (sub-populations had more time to diverge) The evolutionary tree separated one group of Africans from a group containing all five populations. Tree was rooted on branch between groups of greatest difference.,18:49,20 /83,Human Migration Out of Africa,http:/www.becominghuman.org,1. Yorubans 2. Western Pygmies 3. Eastern Pygmies 4. Hadza 5. !Kung,1,2,3,4,5,18:49,21 /83,Two Neanderthal Discoveries,Feldhofer, Germany,Mezmaiskaya, Caucasus,Distance: 25,000km,课堂练习：到NCBI查找这两人的线粒体DNA。,18:49,22 /83,Two Neanderthal Discoveries,Is there a connection between Neanderthals and todays Europeans? If humans did not evolve from Neanderthals, whom did we evolve from?,18:49,23 /83,Carles Lalueza-Fox，2009,The Neanderthal Genome project and beyond,18:49,24 /83,Fig. 3. Schematic representation of the phylogenetic tree of modern humans and Neanderthals, showing also the phylogeny of nuclear genes (the genetic tree). The three examples of nuclear genes, the language gene (FOXP2), the pigmentation gene (MC1R), and the blood group gene (ABO),occupy different positions in the diagram.,Carles Lalueza-Fox， 2009,The Neanderthal Genome project and beyond,18:49,25 /83,The Neanderthal - modern human connection? May 20, 2010 A sixty percent complete, “first draft” of the Neanderthal genome has been prepared by scientists with the Max Planck Institute in Germany and there is evidence there was interbreeding between Neanderthals and modern humans about 80,000 years ago in the Levant. This announcement appeared in the journal Science on May 8 and has had a mixed reception. Colleagues of the Max Planck team are delighted so much progress has been made in defining the Neanderthal genome, so soon after the announcement, a few years ago, of the complete human genome but key figures in the fields of evolutionary biology and paleoanthropology question whether the complex statistical analysis outlined in the paper in fact supports the hypothesis there was interbreeding between the two species. The authors genetic analysis also challenges the “out of Africa” hypothesis which posits we modern humans, Homo sapiens, throughout the world trace our ancestry to anatomically modern humans who migrated out of Africa around 50,000 years ago. The papers Abstract reads: “Neandertals, the closest evolutionary relatives of present-day humans, lived in large parts of Europe and western Asia before disappearing 30,000 years ago. We present a draft sequence of the Neandertal genome composed of more than 4 billion nucleotides from three individuals. Comparisons of the Neandertal genome to the genomes of five present-day humans from different parts of the world identify a number of genomic regions that may have been affected by positive selection in ancestral modern humans, including genes involved in metabolism and in cognitive and skeletal development. We show that Neandertals shared more genetic variants with present-day humans in Eurasia than with present-day humans in sub-Saharan Africa, suggesting that gene flow from Neandertals into the ancestors of non-Africans occurred before the divergence of Eurasian groups from each other.” Science has published a special section, available without the usual subscription requirement. Also the New York Times has an informative account of the Science announcement. The Neanderthals (Homo neanderthalensis) ranged from Spain to southern Siberia and as far south as modern day Israel and Palestine, according to this map, and lived from about 130,000 years ago until their extinction 28,000 years ago.,