Human origins & evolution . How closely related are humans to chimpanzees? see figure 23.3 How Life works o Phylogenetic analysis based on anatomical characteristics had established humans are closely related to chimpanzees o Mary-Claire King and Allan Wilson used molecular techniques in 1975 to determine how closely related the two species are o DNA modules denature, or separate, into two complementary strands at 95? o Non-complementary DNA strands denature at a slightly lower temperature . How closely related are humans to chimpanzees? see figure 23.3 How Life works o Human and chimpanzee DNA was denatured and allowed to form hybrid molecules of complementary sequences that had some mismatches o On average these Human-Chimpanzee DNA hybrid molecules separated at temperature 1? less than human-human DNA molecules o Calibrated against DNA hybridisation in other species this was estimated as a 1% difference in DNA sequences between chimpanzees and humans o Molecular evidence established that humans are more closely related to chimpanzees than any other primate . The evolutionary history of Homo sapiens o Hominins include modern humans and their recent evolutionary ancestors - Neanderthals and Denisovans o The hominin group is mostly related to chimpanzees o Hominins evolved in the last >5 Mya? o Modern humans evolved in the last 500,000 years o Where and when did modern humans evolve? o What evidence has been used to answer this question? . The fossil record gives us information about our evolutionary history o Fossil material has been collected mainly from Africa o Many different species including humans are hominins o All hominins arose after the split from the human/chimpanzee common ancestor o The earliest known hominin, Sahelanthropus tchadensis, is 7 million years old o Ardi, or Ardipithecus ramidus, was capable of walking upright lived 4.4 million years ago (mya) o Lucy, or Australopithecus afarensis, was fully bipedal living ft.2 mya o When and where did the most recent common ancestor of all humans live? o (see "How Life Works" figure 23.10) o Comparison of mitochondrial DNA from 147 people from around the world in the 1980s. o Analysing DNA using restriction enzymes was faster and cheaper than sequencing in the 1980s. o Using 12 restriction enzymes revealed sequence variations between people from different regions. o The relatedness of all the samples was calculated to construct a tree or phylogeny that revealed modern human origins
. When and where did the most recent common ancestor of all living humans live? o Modern humans arose relatively recently in Africa with their most common ancestor living ~200,000 years ago. o This study confirms the "Out of Africa" hypothesis, and disproved the "Multiregional" hypothesis o As we will see later there is also good evidence for the "Out of Africa again and again" hypothesis · Conclusions and summary o Analysis of human mtDNA revealed that modern humans evolved in Africa relatively recently, ~ 200,000 years ago o This study proved the out of Africa theory of human origin and set up a much greater genetic investigation