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D3 human evolution


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Option D3 IB Biology

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D3 human evolution

  1. 1. Option D: Evolution D3 Human evolution WE DID NOT EVOLVE FROM MONKEYS! (And no decent scientist says we did). Instead, we share a common ancestor.
  2. 2. What you need to be able to do and understand:  D.3.1 Outline the method for dating rocks and fossils using radioisotopes, with reference to 14C and 40K.  D.3.2 Define half-life.  D.3.3 Deduce the approximate age of materials based on a simple decay curve for a radioisotope.  D.3.4 Describe the major anatomical features that define humans as primates.  D.3.5 Outline the trends illustrated by the fossils of Ardipithecus ramidus, Australopithecus  D.3.6 State that, at various stages in hominid evolution, several species may have coexisted.  D.3.7 Discuss the incompleteness of the fossil record and the resulting uncertainties about human evolution.  D.3.8 Discuss the correlation between the change in diet and increase in brain size during hominid evolution.  D.3.9 Distinguish between genetic and cultural evolution.  D.3.10 Discuss the relative importance of genetic and
  3. 3. How old is old? The universe is full of naturally occurring radioactive elements. Radioactive isotopes are inherently unstable; over time, radioactive ―parent atoms‖ decay into stable ―daughter atoms.‖ When molten rock cools (igneous rocks), radioactive atoms (isotopes) are trapped inside. Afterwards, they decay at a predictable rate. By measuring the quantity of unstable isotopes left in a rock and comparing it to the quantity of stable daughter isotopes in the rock, we can estimate the amount of time that has passed since that rock formed. Fossils are generally found in sedimentary rock—not igneous rock. Sedimentary rocks can be dated using radioactive carbon-14, but because carbon decays relatively quickly (half-life of 5730 yrs), this only works for rocks younger than about 50 thousand years. So in order to date most older fossils, scientists look for layers of igneous rock or volcanic ash above and below the fossil. We date igneous rock using elements that are slow to decay, such as uranium and potassium (half-life of 1.3 billion years). By dating these surrounding layers, they can figure out the youngest and oldest that the fossil might be; this is known as ―bracketing‖ the age of the
  4. 4. Dating with carbon-14 (14C) Half-life is the period of time it takes for a substance undergoing decay to decrease by half. Watch this short clip on carbon dating C-14 is used to date organic materials.C-14 is formed as the result of the bombardment of Earth by cosmic rays, mostly protons. When the protons crash into atoms high in the atmosphere they create a ton of things, including neutrons. Neutrons that strike the nuclei of nitrogen atoms cause the following reaction:1 0n + 14 7N 14 6C + 1 1p This reaction happens at a relatively steady rate. The carbon atoms then combine with oxygen to produce carbon dioxide. About 1 molecule in each trillion contains C-14 instead of C-12. C-14 decays radioactively with a half-life of 5730 yrs. As long as a plant (or animal) lives, its organic material contains the same fraction of C- 14 as does the atmosphere. When the organism dies, it no longer exchanges C with the atmosphere and the decaying C-14 is not replaced. So the fraction of C-14 to C-12 can be used to determine the time of death of the organism. Carbon dating is only accurate to about 60,000 years- farther than this we have to use other radioactive isotopes…
  5. 5. Dating with potassium-40 (40K) Watch this short clip on radiometric dating- using uranium as an example Potassium-argon dating uses the radioactive isotope potassium-40. Potassium-40 naturally decays to argon gas. These two elements (among others) are contained in volcanic rock. When the rock is molten, it releases gases such as argon into the atmosphere. As it cools and hardens, the volcanic rock traps the gases inside small crystals. The potassium-40 continues to decay into argon gas, but the gas cannot escape the rock. Geologists can melt the rock and measure how much time has passed since the rock was molten. The half-life of potassium-40 is 1.3 billion years. Because it takes at least 200,000 years for enough argon gas to build up to allow accurate measurement, the potassium-argon technique is used to date older objects.
  6. 6. A review of all the different types of dating methods Data analysis activity Go to the VLE and download the word document called ―Working with decay curves‖- this will be graded. You will learn how to analyze half-lives and determine the age of a sample using a simple decay curve like this one:
  7. 7. Why are we primates? Primates include: humans, apes, monkeys, tarsiers, lemurs and lorises. What are the common characteristics for all primates? •grasping limbs, with long fingers and a separated opposable thumb •mobile arms, with shoulder joints allowing movement in three planes and the bones of the shoulder girdle allowing weight to be transferred via the arms •stereoscopic vision, with forward facing eyes on a flattened face, giving overlapping fields of view There are around 230 or so living species of primate, a number which represents only a tiny fraction of all the primate species which have once existed on our planet.
  8. 8. A common ancestor for all primates Read this article on a recently discovered fossil named ―Ida‖: /05/090519104643.htm The fossil is a transitional species – it shows characteristics from the very primitive non-human evolutionary line (prosimians, such as lemurs), but is more related to the human evolutionary line (anthropoids, such as monkeys, apes and humans). At 95% complete, the fossil provides the most complete understanding of the paleobiology of any Eocene primate so far discovered.
  9. 9. What are hominids? The Hominidae are great apes and humans. They form a taxonomic family, including four existing genera: chimpanzees, gorillas, humans, and orangutans. Hominidae is a family within the order Primata which is defined by bipedal locomotion. One trend in hominid evolution includes increasing adaptation to bipedalism, especially forward movement of the foramen magnum. Watch this clip on why chimps, gorillas, and orangutans have 48 chromosomes and humans have 46.
  10. 10. Understanding standing up Anthropologists and evolutionary biologists agree that upright posture and the subsequent ability to walk on two legs was a crucial major adaptation associated with the divergence of the human lineage from a common ancestor with the African apes. Efficient upright walking required numerous changes in the anatomy of the limbs and pelvis and we are the result of the variations and selection pressures that forged this new ability. The ability to walk on two legs was later followed by other human evolutionary trends that lead to tool manufacture and the enlargement of the brain. Can you separate the bones between a chimpanzee and a human? Can you see the small differences that enabled humans to walk upright while chimpanzees have a form of walking called a ―knuckle walk‖ See this recent article on national geographic about a foot fossil
  11. 11. tree This evolutionary tree depicts lines of possible descent for hominids. In other words, it proposes relationships among species over time. All trees are hypotheses, and are based on comparison of living species, fossils, and genetic data. Dashed lines show how related species diverged from each other through a common ancestor. Faded lines indicate very unclear origin or descent. Branch points are called nodes. Nodes indicate a species that once lived, and was the common ancestor of two or more descendants. Horizontal lines indicate time. Orange vertical bars indicate From: oguide/tree.html
  12. 12. Why are there faded lines on the hominid family tree? Because the hominid fossil record is incomplete, it is unclear how the various hominid species are related. Why is the fossil record incomplete? The fossil record for hominids is incomplete because it is difficult for remains of animals living in arid or semi-arid habitats to fossilize. Fossils only form when buried under sediment before decomposition occurs. Another reason is that animal bodies are usually eaten by detritivores, decomposed by bacteria, or broken down chemically. For example, organic acids react with alkali (bases) in bones and teeth therefore, few fossils found of savanna-dwelling hominids. If remains do become fossilized, most remain buried in sediment or may never be found. Hominid fossils that have been found may or may not be representative of hominid history- anthropologists are unsure of their history so more questions may arise. Hominid fossils that have been found are usually partial, and the remainder of the organism must be inferred. These inferences may or may not be correct. As only hard parts of individuals fossilize this leaves many questions concerning the rest of the individual’s phenotype (physical characteristics). A) The complete evolutionary history would show gradual transitions between these forms. (B) A relatively complete fossil record preserves only one of the speciation events, but still shows evidence of gradual change. (C) A typically incomplete fossil record shows only scattered forms through time. (D) Reconstruction of the evolutionary history based on co-occurence and similarity of forms incorrectly shows Species 2 as having evolved from the extinct species, and seriously underestimates the time of
  13. 13. We are going to focus on: •Ardipithecus ramidus •Australopithecus afarensis •Australopithecus africanus •Homo habilis •Homo erectus •Homo neanderthalensis •Homo sapiens As you can see a number of Australopithecus and Homo species probably coexisted
  14. 14. •Australopithecu s sp. purple/gray squares •Homo habilis- dark blue squares •Homo erectus- light blue squares •Homo neanderthalensis - yellow/orange squares •Homo sapiens- red squares Where have we found these fossils?
  15. 15. Ardipithecus ramidus: 5.8 mya - 4.4 mya Go to: bin/splitwindow.cgi?top= /science/top2.html&link= qs/homs/specimen.html for more information on hominid fossils Its age is about 4.4 million years. Ar. ramidus is considerably more primitive than the australopithecines. The skull and brain size are very small, comparable to a chimpanzee. The teeth fossils show that ramidus was omnivorous, unlike chimps which are adapted to a diet of mostly fruit, and australopithecines which were adapted to heavy chewing on abrasive foods. Ar. ramidus also has greatly reduced canine teeth in the males, compared to apes. This is important because in apes canine teeth are important weapons against other males in the social group, so the diminished canines probably indicate a significant change in the social dynamics of ramidus. The leg and pelvis bones show only imperfect adaptation to bipedalism, compared to australopithecines.
  16. 16. Australopithecus afarensis: 3.9 mya - 3 myaA. afarensis which lived from 3.9 to 3.0 million years ago, is one of the first species to appear after the split between emerging hominids and ancestor chimpanzees. It seems to descend directly from Australopithecus anamensis, a species of large ape that lived from 4.2 to 3.9 million years ago. Not surprisingly, there are several points of resemblance between the afarensis and chimpanzee skulls: a wide, apelike face with a low forehead, bony browridges, flat nose, protruding upper jaw, and a massive lower jaw with large back teeth. (The pointed canine teeth, missing from the afarensis fossil, were smaller than those in modern apes.) Both have a brain volume of around 480cc. The shape of the jaw is intermediate between the rectangular shape of apes and the parabolic shape of humans. The larger australopithecine body included changes to the spine, pelvis and leg joints that make walking an effective form of locomotion. Though still capable of climbing and resting in trees, a habitual bipedal posture freed the hands to manipulate, carry and throw objects. Though the finger and toe bones are curved and proportionally longer than in humans, afarensis hands were similar to humans in most ―Lucy ‖
  17. 17. Australopithecus africanus: 3 mya - 2 mya About 3 million years ago, Australopithecus afarensis gave rise to two distinct evolutionary lines: one leading into the first humans, and the other into the robust australopithecines. Though its place is still unclear, A. africanus is most likely the key transitional species toward the emergence of the human line. It's really in the skull that africanus is noticeably different from afarensis: in the more vertical slope of the face, the narrower cheekbones and reduced browridges, and the more rounded shape of the cranium. Brain endocasts show significant increases in the frontal and parietal lobes in comparison to chimpanzee brains; the africanus brain clearly prefigures that of humans. The teeth are also more similar to human teeth than to those of modern apes; the canine teeth are smaller than those in afarensis, and the shape of the jaw is now fully parabolic, again like humans. These features "Taung Child‖
  18. 18. Homo habilis: 2.4 mya - 1.5 mya Discovered by the Leakeys in the early 1960's at Olduvai Gorge in Tanzania. H. habilis lived from about 2.4 to 1.5 million years ago, and is the earliest known species to show novel differences from the chimpanzee and australopithid skulls. The face is still primitive and projecting, but the jaw is pulled under the brain, with smaller molars (though still much larger than in modern humans), and the skull is thinner, with a distinctive rounded shape, vertical sides and a small forehead above the brows. The first humans have arrived on the scene. In habilis, increased brain power coincided with the first known use of manufactured stone or quartz tools (hence the choice of name, which means "handy man‖). Despite its distinctively human cranium and its chronological position near the origin of the human line, habilis had a fairly apelike physical form: its arms were almost as long as its legs. It is therefore
  19. 19. Homo erectus: 1.8 mya – 300,000 yrs ago H. erectus represents a long line of fossils found in eastern Africa, the Middle East and southern and southeastern Asia from about 1.7 million to 200,000 years ago. Erectus shows a gradual lightening of the ergaster features, though many similarities in the skulls (pronounced browridges and an elongated brain case) persist. Indeed, some of the erectus modifications are adaptations for heavy chewing power, and in that sense reflect a radiation into the ecological niches and diets dominated in Africa by the australopithecines. Brain capacity increased gradually throughout the erectus line, from a range of 800cc to 1060cc at the time erectus first appeared to a range of 1060cc to 1300cc around the time it went extinct. Despite its long survival and continually increasing brain size -- and cultural advances that included geographic dispersion throughout southern Asia, the domestication of fire, refinement to Acheulean ―Peking Man‖ ―Java Man‖ ―Chellean Man‖ ―Turkana Boy‖
  20. 20. Homo Neanderthal ensis: 230,000 - 30,000 yrs ago H. neanderthalensis, which lived from about 250,000 to 30,000 years ago, is the last species to diverge from the human line prior to the emergence of modern humans, and the last species of hominid to have gone extinct. Neandertals lived mostly in cold climates, and their body proportions are similar to those of modern cold-adapted peoples: short and stocky with solid limbs. Neandertals had a slightly larger brain capacity than modern humans (1450cc on average, but as large as 1800cc or more), with a developed material culture and some form of spoken language. A large number of tools and weapons have been found from Neandertal sites, all from the Mousterian tool industry. Neandertals were formidable hunters, and are the first people who may have buried their dead, with the oldest known burial site dated to around 100,000 years ago. Like erectus, Neandertals had a protruding jaw, weak chin and receding forehead. The nose and brow also protruded and was probably an adaptation to cold climates. The brain case is longer and lower than that of modern humans, with a marked bulge at the back of the skull. Bones are thick and heavy and show signs of powerful muscle attachments. The extinction of Neandertals coincides in most geographic regions with the arrival of modern humans and the most recent Ice Age. There is no reason to conclude that Cro Magnon man intentionally eradicated the Neandertals. Neandertals already led a difficult, scarring existence. Add to this the final glaciation of their northern ranges, the increased competition with Homo sapiens for large game, and perhaps too the new diseases that the southern immigrants brought with them.
  21. 21. Homo sapiens: 195,000 yrs ago - present Our ancestors seem to have appeared out of some regional subpopulation of Homo heidelbergensis over 130,000 years ago, most likely in the Kenya-Tanzania area of Africa. In sapiens the face is markedly shrunken in relation to the brain, which attains an adult size of 1040cc to 1595cc. The forehead rises sharply, browridges are very small or absent, and the chin is prominent. The skeleton is very gracile; bones are lighter and smoother, without any loss in body size. Compared to the Neandertal skull, modern humans (shown in a Cro-Magnon exemplar) look almost infantile. The cranium seems vulnerably round and delicate. Discovered by workmen in 1868 at Cro-Magnon, in the village of Les Eyzies in France. The estimated age of the site is 30,000 years. The Cro- Magnons lived in Europe between 35,000 and 10,000 years ago. ―Cro-Magnon Man‖ For more information go to:
  22. 22. -who-human-evolution.html Using this online interactive tool can you identify any trends and patterns in Hominid evolution? Trends and patterns in hominid evolution:
  23. 23. Trends and patterns in hominid evolution: When looking at hominid evolution some trends and patterns can see seen: •increasing adaptation to bipedalism, especially forward movement of foramen magnum •increasing brain size in relation to body size •hominids originated in Africa and spread to other continents Ardipithecus fossils found in Ethiopia Australopithecus and Homo habilis fossils found in Southern and Eastern Africa Homo erectus fossils found in Eastern Africa and in Asia Homo neanderthalensis fossils found in Europe Homo sapiens fossils found in all continents except Antarctic •decreasing relative size of: face, jaw, teeth, especially canines; increasing relative size of brain Cranial capacities plotted against time. Key to symbols; triangles, (Australopithecus africanus); squares, australopithecines from South and East African (Paranthropus); circles, Homo (filled, individual specimens; open, group averages) Read more: Brain Size Evolution - Constraints on Brain Size, Selection for Neurological Adaptations, Measuring the Size of Hominid Endocasts, Figure 1 Evolution.html#ixzz17V2mrAlb
  24. 24. Note that as many as 4 or 5 species of early hominids were living at the same time. Observe also that, in at least a half-dozen instances, a parental species continued to exist for a lengthy period of time after a daughter species evolved. The arrangement shown here is not accepted by all paleoanthropologists. For instance, there are some who would merge H. erectus and H. heidelbergensis, considering them as one species. Also, there are those who maintain the H. neanderthalensis is a subspecies of H. sapiens while many others disagree. From:
  25. 25. Early hominids (Australopithecus) brain sizes were similar in size to those of apes today. They had powerful jaws and teeth which indicated a mainly vegetarian diet. About 2.5 million years ago Africa became much cooler and drier, savannah grassland replaced forest which may have prompted evolution of Homo. This change in environment may have caused the development of increasingly sophisticated tools for a change to hunting and killing large animals instead of a vegetarian diet. The increasing meat in diet corresponds to the start of increase in hominid brain size in early hominids. Brain growth slows after birth but Homo has rapid brain growth after birth as well. How could this happen? 1. Eating meat increases supply of protein, fat and energy, making larger brain growth possible. 2. Hunting and killing prey on savannas is more difficult than Could a change in diet bring larger brains? Read this article on diet and brain size in early hominids: evolution-another-item-on-the-menu_a-27- 1088.html
  26. 26. Two TED talks on hominid evolution:
  27. 27. entific_Process/01.html To sum it all up!
  28. 28. Nature Vs. Nurture? Which do you think plays the bigger role in human evolution? Diseases show a continuum. Some, such as Down's Syndrome, are completely genetic in origin, while others, such as scurvy, are completely environmental. But most diseases — ulcers, for example — are somewhere in the middle: people with different genes will react
  29. 29. Genetic Evolution- “NATURE” Cultural Evolution- “NUTURE”  inherited vertically between generations  physically inherited as genes coded within DNA  change is random, through mutation  natural selection determines likelihood of inheritance  occurs slowly as gene pools alter gradually  inherited vertically, horizontally, or between any group, across any time or distance  inherited physically or non- physically, independent of DNA  change can be random or directed by intelligence  selection determines likelihood of inheritance  can occur at any rate, typically much more rapidly than genetic evolution, and even instantaneously Read this article from Wired Science:
  30. 30. Genetic Evolution- “NATURE” Cultural Evolution- “NUTURE”  genes produce the abilities to learn language  genes produce the abilities to learn about natural history  genes produce the abilities to learn complex social information  culture produces specific languages  culture produces specific natural history information  culture produces specific complex social information There is no nature without nurture, and no nurture without nature Is the product of selection for genes producing large brains which are capable of learning. Is the specific learning done by groups of people sharing similarly selected large brains.
  31. 31. Why are cultural AND genetic evolution important? Cultural evolution has played an increasingly greater role in the lives of humans over time, especially over the past few thousand years, during which human characteristics have changed hugely. Genetic change happens too slowly to produce the huge changes in human culture. Some cultural changes have, such as medical advances, reduced natural selection pressures between phenotypes. The last word… s/humankind/index.html
  32. 32. Read this article for a good chuckle on what we have inherited nature/The-Top-Ten-Daily-Consequences- of-Having-Evolved.html including a reason for hiccups and goosebumps!