Hominin Evolution - Human EvolutionAims:
Must be able to outline the main stages of Human evolution.
Should be able to compare and contrast the main hypotheses for Human evolution.
Could be able to discuss the current and possible future evolutionary trends.
The illustration below was in common usage in the popular press 30 years ago to represent the linear progression from a primitive ape-like ancestor to modern humans.It is still used in advertising as a visual metaphor for the idea of evolution.Human Evolution: a 1960s View
Predictions According to the Linear Progression ModelThe fossil record should consistently show smooth inter-gradations from one species to the next.Human Evolution: a 1960s View The Actual Evidence Observed in the Fossil RecordFew smooth inter-gradations from one species to the nextSpecies tend to appear suddenly in the fossil recordThe species linger for varying but often very extended periods of time in the fossil recordThe species disappear as suddenly as they arrivedThey are replaced by other species which might or might not be closely related to them.
Human Evolution: a Modern ViewA modern view of human evolution maintains that it has occurred as a series of adaptive radiations.The 1st radiation: Early bipedal apes including the australopithecines.The 2nd radiation: Involved genus Paranthropus, group of species that exploited low-grade vegetable food sources (nuts, root tubers and seeds) resulting in (megadont) species with very large teeth.3rd radiation: Genus Homo, with the habilines and erectines developing a larger brain, diversifying, and dispersing from Africa to other parts of the Old World.Last radiation: does not involve major evolutionary divergence, reflects dispersal of modern humans worldwide.Source: Ian Tattersall, The Fossil Trail, Oxford University Press (1995)DiversityTime (millions of years)African apesMegadontsEarly Bipedal Apes
Human Evolution TimelineHomo sapiensH. neanderthalensisH. heidelbergensisH. erectusH. antecessorH. habilisH. ergasterH. rudolfensisKenyanthropus platyopsAustralopithecus anamensis Australopithecus bahrelghazali Au. afarensis Au. africanus Au. garhi Chimpanzees (Pan)Paranthropus boiseiP. robustusP. aethiopicusArdipithecus ramidusOrrorin tugenensisSahelanthropus tchadensisMillions of Years012345678H. floresiensis
The Origin of Modern HumansThere are two theories accounting for the origin of anatomically modern humans (Homo sapiens):African originHomo erectusArchaicHomo sapiensModernHomo sapiensAfrican originMulti-regional HypothesisReplacement Hypothesis(Out of Africa / Eve Hypotheses)Gene flowExtinction
The Replacement HypothesisAlso known as the Out of Africa Hypothesis and Eve Hypothesis.
All modern humans can trace their evolutionary heritage to a single woman via changes in mitochondrial DNA.
This woman, 'Eve', lived about 200 000 years ago in Africa.
The descendants of this population of modern humans dispersed throughout the rest of the world, displacing all other human populations in existence at the time.Present0.5 mya1.0 myaAfrican originHomo erectusArchaicHomo sapiensModernHomo sapiens
The Multiregional HypothesisThis theory is based largely on the fossil evidence and the anatomical characteristics of modern populations.
The mitochondrial DNA data can be interpreted in a variety of ways, one of which supports a multi-regional origin of modern humans.
Modern human populations can be traced back in the fossil record to about 1 million years ago when Homo erectus first left Africa.
Continuous gene flow occurred between regional populations.Homo erectusArchaicHomo sapiensModernHomo sapiensPresent0.5 mya1.0 myaAfrican origin
Dispersal of Modern HumansQafzeh120 000-92 000 yaOmo195 000 yaBorder Cave115 000-62 000 yaKlasies River Mouth120 000-84 000 yaSkuhl101 000-81 000 yaThis map shows a probable origin and dispersal of modern humans throughout the world.An African origin is almost certain, with south eastern Africa being the most likely region.ya = years ago
Dispersal of Modern HumansCro-Magnon 30 000 yaLake Mungo31 000 yaMalakunanja II50 000 yaQafzeh120 000 - 92 000 yaOmo195 000 yaBorder Cave115 000 - 62 000 yaKlasies River Mouth120 000 - 84 000 yaSkuhl101 000 - 81 000 ya
Human Biological EvolutionNatural selection has acted over generations on inherited phenotypes and as a result changes have occurred in reference to survival and reproduction. Evidence of this can be seen in:Physical traitsBiochemical traitsPhysiological traitsVariation in height, weight, skin colour, hair texture etcVariation in blood type, enzyme concentration, hormones etcVariation in tolerance to foods, temperature, metabolism etc
ActivityAnswer the questions on pages 383 to 391 and 395/6 in the Biozone books.
Present and Future EvolutionOver the next few thousand years, human evolution will be influenced by a number of new factors:Natural selection pressures may select for beauty, intelligence, body symmetry, disease resistance, and tolerance to pollutants and electromagnetic radiation.Genetic engineering may introduce new and possibly novel genes to add new traits.Gene therapy may replace, remove, or turn off unwanted, perhaps harmful, genes.Nanotechnology may provide a means to tinker with anatomy and physiology at the cellular level to repair or enhance function.Prosthetic enhancements and implants (although not inherited) may extend human performance beyond its present, natural range.
ActivityAnswer the questions on page 400 in the Biozone books.