Hominin Evolution - Human Evolution

1. Hominin Evolution - Human Evolution • Aims: • 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.

2. Evolving lineage with the accumulation of gradual genetic changes under the influence of natural selection Human Evolution: a 1960s View • 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.

3. Human Evolution: a 1960s View • The Actual Evidence Observed in the Fossil Record • Few smooth inter-gradations from one species to the next • Species tend to appear suddenly in the fossil record • The species linger for varying but often very extended periods of time in the fossil record • The species disappear as suddenly as they arrived • They are replaced by other species which might or might not be closely related to them. • Predictions According to the Linear Progression Model • The fossil record should consistently show smooth inter-gradations from one species to the next.

4. Human Evolution: a Modern View • A 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 2ndradiation: 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. Megadonts Time (millions of years) African apes Early Bipedal Apes Source: Ian Tattersall, The Fossil Trail, Oxford University Press (1995) Diversity

5. Archaic and Modern Humans: Rapid advances in brain size; suite of new behaviors. Anatomically modern humans emerge from one of the many regional variants. Erectines: Body height of modern proportions. Increasing brain volume. Sophisticated tools are manufactured and used to kill and process small sized game. Australopithecines: Possessed a gracile body form and were probably opportunistic omnivores/scavengers. Habilines: Brain enlargement, first recognizable stone tools, body remains small/slight. Paranthropines: Early hominids specialized for eating a bulky, low-grade vegetarian diet. Developed powerful chewing muscles and a generally robust skull. Early Hominids: Brain size similar to modern chimpanzees, body remains small/slight. Hominid status may be in question. Human Evolution Timeline Homo sapiens Chimpanzees (Pan) 0 H. heidelbergensis H. neanderthalensis H. erectus H. floresiensis Paranthropus boisei 1 H. antecessor P. robustus H. habilis 2 H. ergaster Au. garhi H. rudolfensis P. aethiopicus 3 Kenyanthropus platyops Au. africanus Australopithecus bahrelghazali Millions of Years 4 Australopithecus anamensis Ardipithecus ramidus Au. afarensis 5 Orrorin tugenensis 6 Sahelanthropus tchadensis 7 8

6. Present 0.5 mya 1.0 mya The Origin of Modern Humans • There are two theories accounting for the origin of anatomically modern humans (Homo sapiens): Replacement Hypothesis (Out of Africa / Eve Hypotheses) Multi-regional Hypothesis Modern Homo sapiens Archaic Homo sapiens Extinction Gene flow Homo erectus African origin African origin

7. The Replacement Hypothesis • Also 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. Modern Homo sapiens Present Archaic Homo sapiens 0.5 mya Homo erectus 1.0 mya African origin

8. The Multiregional Hypothesis Modern Homo sapiens • This 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. Present Archaic Homo sapiens 0.5 mya Homo erectus 1.0 mya African origin

9. Probable area of origin for modern humans some 200 000 years ago Dispersal of Modern Humans • This 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. Skuhl 101 000- 81 000 ya Qafzeh 120 000- 92 000 ya Omo 195 000 ya Border Cave 115 000-62 000 ya Klasies River Mouth 120 000-84 000 ya ya = years ago

10. Probable area of origin for modern humans some 200 000 years ago Humans travel to the Americas between 30 000- 15 000 years ago Australia was first occupied at least 50 000 years ago Polynesia populated progressively 4500 - 700 years ago The first modern humans appear in Europe 40 000 - 35 000 years ago Earliest dating in East Asia is 67 000 years ago in southern China Dispersal of Modern Humans Cro-Magnon30 000 ya Skuhl 101 000 - 81 000 ya Qafzeh 120 000 - 92 000 ya Omo 195 000 ya Malakunanja II 50 000 ya Lake Mungo 31 000 ya Border Cave 115 000 - 62 000 ya Klasies River Mouth 120 000 - 84 000 ya

11. Human Biological Evolution • Natural 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 traits • Biochemical traits • Physiological traits Variation in height, weight, skin colour, hair texture etc Variation in blood type, enzyme concentration, hormones etc Variation in tolerance to foods, temperature, metabolism etc

12. Activity Answer the questions on pages 383 to 391 and 395/6 in the Biozone books.

13. Present and Future Evolution • Over 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, diseaseresistance, 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. • Prostheticenhancements and implants (although not inherited) may extend human performance beyond its present, natural range.

14. Activity Answer the questions on page 400 in the Biozone books.