Week 9 Notes
Week 9 Notes GE 70B
Popular in Evolution of Life and the Cosmos
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General Education Cluster 80A Frontiers in Human Aging
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This 5 page Class Notes was uploaded by Sarah Doberneck on Saturday March 12, 2016. The Class Notes belongs to GE 70B at University of California - Los Angeles taught by Dr. Friscia in Winter 2016. Since its upload, it has received 46 views. For similar materials see Evolution of Life and the Cosmos in General at University of California - Los Angeles.
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Date Created: 03/12/16
Competing Views of the Spread of Modern Humans Out of Africa o Modern humans arise in Africa and replace archaic humans o Homo erectus in Asia as regional dead end, unrelated to modern humans o Homo erectus in Africa as a different species (H. ergaster/heidelbergensis) that eventually leads to modern humans Multiregional o Worldwide species of humans with lots of interbreeding across their range o Homo erectus everywhere evolves into modern humans The answer is somewhere in between o It is thought that the lineages that spread out of Africa did not evolve into humans, and humans developed in Africa o However, it’s not that simple because of variation throughout Africa Assimilation Model o Neanderthals as a European sister group to modern humans Descendants of Homo erectus in Eurasia (maybe...) o Along with Denisovians they added to the modern human genome o We can see bits of Neanderthal genes in modern humans 1-4% in non-Africans o Denisovian genes are found in Melanisians o So were the Neanderthals & Denisovians different species or races? Mitochondrial Eve backs up an African origin of modern humans o Cann et al. 1987 – mtDNA tree based on 147 people. o Shows that there was one female African individual whose ancestors survived to modern times o Divergence time around 200 kya from a population of about 10,000 individuals How and when did modern humans get out of Africa? “Northern” Route o Through the Levant (Middle East) into Eurasia o Departure ~100kya o Early tools in Asia back this up “Southern” Route o Through Horn of Africa (Ethiopia/Somalia) into southern Asia • Departure around 60kya o Similar environments along the way o Genetics backs this up – A genetic haplotype shared with populations Africa and Asia is dated to 70kya o Linguistics also backs an entry into Europe from south Asia Genus Homo Review This is the lineage where brain increase happens Homo erectus is the first hominid to leave Africa, and enter Europe and Asia They are also the first to leave evidence of stone tools Neanderthals were a separate (sub-) species of Homo (sapiens). Homo sapiens spreads to the New World and Australia Human Genetic Diversity Human genetic diversity is low – Less then chimps or gorillas Africans show the most diversity o If only Africans were left alive after a great cataclysm, they would retain 93% of present genetic variation o If only the Xhosa people of S. Africa survived there would be 80% of the genetic variation left. • More variation is within “ races ” than between “ races ” o 85% of genetic diversity is between individuals within a nation or tribe, and this isn’t affected by how you divide up the world (FST = .15) o ~10% between local populations within “races” – Only ~6% is between classically defined “ races ” How is this possible? So what is ‘race’? Biological definition o population separated by geographic distance and distinguishable by phenotype and genotype In humans, this certainly isn’t the case. o There’s lots of admixture (migration, colonialism, travel, etc.) o Human ‘races’ have been divided up many different ways, with no agreed upon taxonomy o Most ‘races’ are cultural definitions, backed up by one or two key phenotypic traits (e.g., skin color) So self-reporting often works fine What about skin color? Skin color is controlled by ~70 loci which control a number of factors: o Proportion of two different types of melanin o Size of melanosomes o Location of melanosomes The earliest humans out of Africa were probably dark-skinned Most variation is probably due to natural selection for: o Dark skin for protection against UV radiation (in tropical areas) o Light skin for vitamin D production (in polar areas) What about Africa? Projects are working to document genetic diversity within Africa: o Southern African Human Genome Programme o Human Heredity and Health in Africa (H3Africa), o Both strive to do the work in Africa and build the necessary infrastructure to do so o “Genomic Sovereignty” More recently the African Genome Variation Project has done a wider search o 1481 individuals from 18 ‘ethno-linguistic’ groups Focused on Eurasian admixture & selection Human Development Review Upright walking + large brains = problems in birth (canal too small) The ontogeny of humans is an example of heterochronic growth Humans are paedomorphic apes, and are born altricial, whose bodies grow allometrically and whose heads grow isometrically It also means that humans are dimorphic, especially in the hips Models of Human Evolution So why did humans evolve this weird upright stance and overdeveloped brains if it causes so many problems? One hypothesis o More arid environment leads to trees further apart so hominids have to move across ground o More aridity leads to even less trees to hominids can’t escape so they get bigger brains to be able to defend themselves o Luckily their hands were no free from walking upright so they could take care of their altricial offspring Another hominid evolution scenario by C.O. Lovejoy (KSU) o The evolution of hominids is related to SEX o Chimp-like ancestor evolved to reduce infant mortality (which is high among chimps) and have more offspring o In order for the female to care for the baby, males must forage for food (provisioning the females) o They have to bring the food back, so they walk upright o Males must know that the baby they’re helping to feed is theirs, so hominids moved away from polygamy to monogamy o “Human females are continually sexually receptive (79)”, which may have been selected for, along with other epigamic (sexual) characters: Lack of big canines in males Constantly enlarged mammae Oddly placed hair o Big brains develop from longer offspring care times and a feedback of developing culture Welcome to the Anthropocene (Recent, Rapid Climate Change) Thursday, March 3, 2016 11:03 AM Evolution continues… the big brained ape is now in charge Short time horizon of human experience o Exploitation of local environments Technology: tools---speed up change o Exploitation of depletable resources o Dramatic increase in success of humanity Population Growth Technology has allowed humans to increase our carrying capacity But even this will reach a limit Earth is habitable because greenhouse gases, notably H2O and CO2, trap ling wave radiation which increase the average global temperature from -17C to 15C The gases make it so that it gets warmer as you go toward the surface This keeps the oceans from freezing on average The greenhouse effect Part of Earth's outgoing thermal radiation is captured by some atmospheric constituents like H10 CO2 O3 etc. Greenhouse gases act like a blanket So the greenhouse effect is a naturally occurring phenomenon that is helpful to life on earth Ok, then what’s wrong with emitting more CO2 into the atmosphere? o Anthropogenic emissions of GHGs are creating too much The Carbon Cycle Lithosphere. Hydrosphere, atmosphere, biosphere are all connected through cycling carbon The Slow Carbon Cycle Through a series of chemical reactions and tectonic activity, carbon takes between 100-200 million years to move between rocks About 80% of carbon containing rocks is carbonate The remaining 20% is organic (reduced) carbon From the Slow to Fast Carbon Cycle Some biomass can be sequestered in environments where it is not easily oxidized Under some PT conditions, oxygen can be removed from the carbohydrates producing reduced organic matter If they are concentrated, trapped, and extracted… these are fossil fuels Over 80% of energy in the US is derived from fossil fuels In recent years, this has gone down and use of renewable energy sources has increased This is caused by economic reasons (it’s cheaper) rather than people actually caring about global warming Added greenhouse gases will warm the climate, how the earth will respond is uncertain For a given concentration of GHGs the amount of heat trapper can be calculated precise This is called greenhouse radiative forcing Is the climate warming now? First the observations o Based on data of the global average temperature from the last 100 years, there has definitely been an increase in temperature. Around 1960 it became very clear that the temperature has not been consistent o Since the early 20th century, earths mean surface temp has increased by about .8C with about 2/3 of the increase covering since 1980 o 2005, 2010 had been tied for warmest years in the past 1000 years, 1998 was a close second o 2014 now hottest year on record sink e1880 o 2002, 2003, 2006, 2007 follow o The largest temperature increases are in the artic and the Antarctic peninsula Are increases in greenhouse gases related to or a direct cause of the increased surface temperatures? o Well sun activity has decreased while temp has increased so you can’t blame it on the sun o Fluctuations of temperature and concentration of carbon dioxide follow each other until recently when they both rise very suddenly o The geological record contains evidence that natural increases in CO2 concentration Summary: Cenozoic Era Dominant Forcing: Natural CO@ o Rate -100 ppm/My o Human made rate today -2 ppm/yr. o Humans overwhelm show geologic changes Climate sensitivity is high People expect that the sea level will rise by a few feet
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