Lecture 34 notes.docx

Introduction to Human Evolution Friday, December 8th Homo sapiens emergence can be seen behaviorally rapid pace of change in the Upper Paleolithic or Later Stone Age appearance of symbolic behavior The origins of modern humans Multi-regional evolution Replacement Multiregional and Replacement...

Introduction to Human Evolution Friday, December 8th Homo sapiens emergence can be seen behaviorally rapid pace of change in the Upper Paleolithic or Later Stone Age appearance of symbolic behavior The origins of modern humans Multi-regional evolution Replacement Multiregional and Replacement Models Replacement Localized african origin Replaced Indigenous hominids Proposes anatomically modern populations arose in Africa in the last 200,000 years Migrated from africa, completely replacing pre-modern populations in Europe and Asia does not account for the transition from premodern forms to H. sapiens anywhere except Africa. Multiregional Models Gene flow the interchange of genes between different populations the flow of genetic material interbreeding, passing material on through generations Repeated migration Populations, connected by gene flow, in Europe, Asia, and Africa continued evolutionary development Predictions Replacement predicts sapien fossils in Africa first Multi-region predicts a single lineage What is known about the origins of modern humans? Anatomically modern humans appear first in Africa (consistent with both models) modern humans reach the near east by 120-80 kyr, but they do not reach Europe. Their presence in Asia at this time is disputed (consistent with both models) by 45-35 kyr, modern humans colonize Europe and asia with other archaic humans What is know about the origins of modern humans? Between 55-40 kyr, Neanderthals and modern humans interbreed i the NEar east and Europe (consistent with multiregional evolution, but not replacement) Eurasian populations diverge from African populations only ~45 kyr. (consistent with replacement but not multiregional evolution) Genetic variability is much greater in African populations than in Eurasian populations (consistent with replacement but not multiregiona) Thus, modern humans from Africa, appear to have replaced Neanderthals and other archaic humans in Eurasia, but with some hybridization In sum…. Replacement Replacement with hybridization Multiregional      Traditional concept of race Since the 1600s, race has been used to refer to culturally defined groups Race is used as a biological term, but has enormous social significance From a biological standpoint, race as we know it as we know it culturally it holds no weight below the surface Based on phenotypic expression, outward expression of genetic material In any racial group, there will be individuals who fall in the normal range of variation for another group for one or several characteristics Clinal distributions a cline is a gradual change in the frequency of a trait or allele in populations dispersed over geographical space example: the distribution of the A and B allele in the Old World Clinal distributions are thought to reflect natural selection and/or gene flow Consequently, clinal distributions are explained in evolutionary terms Human Biological Evolution Humans live in cultural environments that are continually modified by their activities Evolutionary processes can be understood only within this cultural context Adaptive significance of Human Variation Human variation is the result of adaptations to environmental conditions Physiological response to the environment operates on two levels Long term: evolutionary changes characterize all individuals within a population or species Short term: temporary physiological response is called acclimatization Acclimatization Physiological responses to changes in the environment Responses may be temporary or permanent, depending on the duration of the environmental change and when it occurs Because it is under genetic influence, acclimatization is subject to natural selection and genetic drift UV radiation Considering the cancer causing effects of UV radiation from an evolutionary perspective Early hominins lived in the tropics, where solar radiation is more intense than in temperate areas to the north and south Unlike modern city dwellers, early hominids spent their days outdoors Early hominins didn’t wear clothing that would have protected them from the sun Thermal environment Mammals and birds have evolved complex physiological mechanisms to maintain a constant body temperature Humans are found in a wide variety of thermal environments, ranging from 120 F to -60 F Why it matters One goal of the human genome project is to find DNA variants associated with disease and to design treatment that target those genes Because some of these variants cluster in certain populations, there have been efforts to identify ancestry to predict risk has led to race-based medicine Why is matters The result has been the use of the imprecise term for race to design treatment protocols There are several problems with this effort Clinically observed or self-Id of race or ethnicity is often not congruent with genetic profiles If treatment is assigned for a person based on self-reported race rather than a genetic test, serious illnesses may be missed The use of race as a basis for treatment ignores real differences that lead to ill health