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Human Evolution. Tibor Cemicky. Tracing Human Evolution. Our understanding of human evolution is based mostly on fossils Hominid fossil record contains many gaps
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Human Evolution Tibor Cemicky
Tracing Human Evolution • Our understanding of human evolution is based mostly on fossils • Hominid fossil record contains many gaps • Only a tiny proportion of animal bodies became fossilized (most was eaten by detrivores, decomposed by bacteria or broken down chemically) • Hominid fossils consist of bones and teeth only • These remains were preserved because they were covered by dry sediments
Problems with tracing human origins and evolution • Because there are gaps in the hominid fossil record it‘s hard to say how different species of hominid are related • Many details of human evolutionary origins are also uncertain • Discoveries of small number of fossils can cause major changes in the prevailing theories
Dating Fossils • To place fossils into a sequence it is necessaey to know their dates • To find these dates we use radiotopes (radioactive isotopes of chemical elements) • When an atom of a radioisotope decays, it changes into another isotope and gives of radiation • The rate of decay varies between different radioisotopes and is called the half-life • Half life is the time it takes for the radioactivity to fall to half of its original level • The two most commonly used radioisotopes for dating fossils are 14C and 40K • Half-life of 14C is 5370 years and half-life of 40K is 1250 million years
Hominid Diets and Brain Size • The brains of the early hominids (Australopithecus) were only slightly larger than the brains of apes • Their strong jaws indicate vegetarian diet • About 2.5 million years ago Africa became much cooler and drier and forest was replaced by savannah grassland • This change of habitat might be the reason behind the evolution of the first species of Homo • Development of increasingly sophisticated tools led to a change in diet that included meat obtained by hunting • This change in diet corresponds with the start of increase in brain size
Increase in Brain Size • The increase in brain size can be explained in two ways: • Eating meat increased the supply of protein, fat and energy making it possible for the growth of larger brains. • Catching and killing prey on the savannas was more difficult than gathering plant foods so natural selection favoured hominids with larger brains and greater intelligence
Genetic and Cultural Evolution • The large brain of Homo sapiens and other species of Homo allows much to be learned during both childhood and adulthood • Language, tool making skills, hunting techniques, methods of agriculture, regilion and many other forms of behaviour are passed from generation to generation by teaching and learning • New methods, inventions or customs can be incorporated into what is passed on. • This process is called Cultural evolution and is different from Genetic evolution
Cultural vs. Genetic Evolution • Cultural evolution does not involve changes in allele frequencies in the gene pool • Changes due to cultural evolution can happen during human life time, genetic evolutions happens over generations • Cultural evolution involves characteristics aquired during a person‘s life, genetic characteristics are inherited • Cultural evolution is responsible for most of the changes in the lives of humans in the last few thousand years • Genetic evolution has been reduced recently due to cultural evolution (e.g medicine restricts natural selection)