This document provides an overview of topics related to human evolution, including: - Methods for radioactive dating of rocks and fossils using carbon-14 and potassium-40 isotopes. - Key anatomical features that define humans as primates, such as grasping limbs and binocular vision. - Major trends seen in hominid fossils like Ardipithecus, Australopithecus, and Homo species showing brain size increase and facial shortening over time. - Potential for multiple hominid species to coexist and uncertainties due to an incomplete fossil record. - Relationship between increased brain size and diet change in hominids, correlated with meat consumption. - Distinction between genetic evolution through natural selection

1. IB Biology Option D D3 Human Evolution Jason de Nys All syllabus statements ©IBO 2007 All images CC or public domain or link to original material. http://commons.wikimedia.org/wiki/File:LB1_skull.jpg http://commons.wikimedia.org/wiki/File:Human-evolution.jpg

2. D.3.1 Outline the method for dating rocks and fossils using radioisotopes, with reference to 14C and 40K. 14C is a naturally occurring isotope of carbon with a half life of 5730 years It is constantly being made in the atmosphere when cosmic rays cause neutrons to fuse with nitrogen nuclei and “kick out” protons Decay Formation 14C production is in equilibrium with its decay to 12C The 14C is incorporated in carbon dioxide which is then taken up by plants. In the end all living things have the same ratio of 14C to 12C When an organism dies it no longer takes in 14C. So over time the ratio of 14C to 12C changes. This is measurable and can be used to estimate age. The limit for accurate determination of age is about 50,000y http://en.wikipedia.org/wiki/File:Carbon_14_formation_and_decay.svg

3. 40K is an isotope with a half life of 1.3 X 109 y It decays to 40Ar. When 40K is released from a volcano in lava all of the argon gas is driven off. So brand new rocks effectively have a ratio 40K:40Ar of 100:0 Over time the lava may be weathered and eroded and incorporated into sedimentary rocks. The measured ratio of 40K to 40Ar can be used to date rocks over one million years old with an accuracy of around 50000 years

5. D.3.2 Define half-life. The time it takes for half of a radioactive isotope to decay Simulation of many identical atoms undergoing radioactive decay, starting with either four atoms (left) or 400 atoms (right). The number at the top indicates how many half-lives have elapsed http://en.wikipedia.org/wiki/File:Halflife-sim.gif

6. http://en.wikipedia.org/wiki/File:Plot-exponential-decay.svg What is the half life for each of the isotopes represented by these curves?

7. ?.?? 3.42 0.13 0.7

8. D.3.3 Deduce the approximate age of materials based on a simple decay curve for a radioisotope. Play the game

9. D.3.4 Describe the major anatomical features that define humans as primates. human gibbon gorilla Grasping pentadactyl limbs http://www.flickr.com/photos/johnkay/5901639745/ http://www.flickr.com/photos/shannonkringen/5466678956/ http://www.flickr.com/photos/grendelkhan/1160017887/

10. Binocular Vision http://www.flickr.com/photos/kevenlaw/2260970300/ http://www.flickr.com/photos/pezz/447411079/ http://www.flickr.com/photos/tambako/5289604279/ http://www.flickr.com/photos/maessive/62526827/ http://www.flickr.com/photos/patries71/3038074728/

11. Reduced snout leading to reduced olfaction Monkey Squirrel vs. Doggie http://www.flickr.com/photos/21185968@N00/3760968061/ http://www.flickr.com/photos/tomitapio/4566585948/ http://www.flickr.com/photos/aechempati/5419119893/ http://www.flickr.com/photos/tambako/4561359690/sizes/l/in/photostream/ Human

12. Human Baboon Gorilla Generalised Dentition Moo Cown http://www.flickr.com/photos/philman/2755063715/ http://www.flickr.com/photos/patries71/3149890871/ http://www.flickr.com/photos/mugley/3280473929/ http://www.flickr.com/photos/plasticbrain/4243519977/

13. Others: Forelimbs able to twist Clavicle allows wide range of arm movement (re. the above two points: if you have a gentle and patient pet dog, give it a rub on the tummy and then move it’s forelegs, they really only move in one plane) Slower reproduction - long gestation - usually one offspring at a time Larger skull – relative to body size Large brain – more complex, more folds Better visual acuity – more of the photoreceptors have their own sensory neurons Social dependency

14. D.3.5 Outline the trends illustrated by the fossils of Ardipithecusramidus, Australopithecusincluding A.afarensis and A. africanus, and Homo including H. habilis, H. erectus, H. neanderthalensisand H. sapiens.

15. http://commons.wikimedia.org/wiki/File:Ardi.jpg http://commons.wikimedia.org/wiki/File:Australopithecus_afarensis_reconstruction.JPG http://commons.wikimedia.org/wiki/File:Australopithecus_africanus_face1_(University_of_Zurich).JPG http://commons.wikimedia.org/wiki/File:Homo_habilis-KNM_ER_1813.jpg http://commons.wikimedia.org/wiki/File:Broken_Hill_Skull_(Replica01).jpg http://commons.wikimedia.org/wiki/File:Homo_sapiens_neanderthalensis.jpg http://www.flickr.com/photos/53898309@N00/2211288333/ Skulls not to scale Ardipithecusramidus Australopithecus africanus Australopithecus afarensis Homo erectus Homo habilis Homo neanderthalensis Homo sapiens

16. 1. Gorilla 2. Australopithecine 3. Homo erectus 4. Neanderthal (La-Chapelle-au-Seine) 5. Steinheim Skull 6. Modern human http://commons.wikimedia.org/wiki/File:Craniums_of_Homo.svg

18. shortening of the face

19. loss of brow ridgesYou can’t really see it but the hole in the bottom of the skull where the spinal cord exits the brain (foramen magnum) is further forward in modern humans. This distributes the weight of the head over the spine so that modern humans do not need huge necks muscles.

20. Homo sapiens Pan troglodytes (chimpanzee) http://pandasthumb.org/archives/2006/09/fun-with-homini.html http://commons.wikimedia.org/wiki/File:Human_and_chimp_brain.png

21. The jaw has developed from a U into a V shape. Teeth have generally reduced in size. (Chimpanzee provided for comparison)

22. Human hands are adapted for grasping and fine manipulation. In contrast gorillas have short fingers for knuckle walking and gibbons have elongated fingers and reduced thumbs for brachiating. http://www.flickr.com/photos/docsearls/5500125757/ http://en.wikipedia.org/wiki/File:Western_Lowland_Gorilla.jpg http://www.flickr.com/photos/cskk/2709688102/

23. Skeleton, locomotion and posture Human knees aligned under the body’s centre of gravity because femurs are angled inwards. Human legs straighten completely when walking. Human spine has additional curves to keep centres of mass of head and trunk aligned for bipedalism. Big toe not opposable in humans, which allows for an arched foot. Ratio legs:arms greater for humans than other apes Human pelvis broader

25. Small teeth and reduced numbers of teeth

26. Prolonged growth period

27. Long life span

28. Flat face and thin skull bones

29. Lactase production in adults

30. Epicanthic eye fold

31. Small nose

33. http://en.wikipedia.org/wiki/Human_evolution

35. Note that according to this interpretation of the fossil record Homo sapiens is not descended from Homoerectus or Homo neanderthalensis. However, some postulate that Homo sapiens may have hybridised with Homo neanderthalenis. This could have contributed to the disappearance of the neanderthalsin much the same way that indigenous animals like dingos are in danger of extinction due to breeding with domestic dogs. http://en.wikipedia.org/wiki/File:Humanevolutionchart.png

36. TOK Read the article on Wikipedia about Homo floresiensis Discovered in 2004 on the Indonesian island of Flores, it has stirred up controversy in the palaeoanthropological world. Is it a separate species or is it the remains of diseased Homo sapiens. You be the judge! Short PBS video

38. Scavengers usually break up skeletons and even chew up bones

39. The conditions have to be just right for fossilisation to occur.

41. The large gaps in the human evolution fossil record are consistent with punctuated equilibrium The following four slides show how the gaps are filled over time with new discoveries. The graphs plot cranial size against the age of the fossil. http://www.flickr.com/photos/prfr/3196435827/

42. 1850 http://en.wikipedia.org/wiki/Transitional_fossil

43. 1900 http://en.wikipedia.org/wiki/Transitional_fossil

44. 1950 http://en.wikipedia.org/wiki/Transitional_fossil

45. 2002 http://en.wikipedia.org/wiki/Transitional_fossil

46. Despite the fossil evidence we have so far, there are still large gaps in our knowledge We have no fossil for the last common ancestor of humans and chimpanzees It is believed to have lived 6-8 million years ago Find out how this estimate was determined http://www.flickr.com/photos/owenbooth/126288240/

48. Mastery of fire

49. Cooking

50. Wamth

51. Protection

52. Greater behavioural flexibility (less reliance on instinct and better able to learn and pass on knowledge necessary to adapt to an environment)http://madsenworld.dk/anigif/light/flames.gif http://commons.wikimedia.org/wiki/File:Miscellaneous_stone_tools.jpg

54. Years of development before young can look after themselves

55. Much more brain development occurs post birth that for any other animalIn summary: Big brains are energetically expensive. The mother must take in lots of energy not only during pregnancy, but for a significant time after. Hominids needed to increase their energy uptake. http://www.flickr.com/photos/superbomba/2288271254/

56. The solution to this energy crisis was to swap a diet of these: http://www.flickr.com/photos/heydrienne/22080973/

57. For some chunks of this: The increase in brain size observed in hominid fossils has been closely correlated with an increased intake of meat. A bigger brain made hunting and killing easier

58. D.3.9 Distinguish between genetic and cultural evolution. Well gosh, we know all about genetic evolution by now! In this context it refers to the genetic changes that have occurred during the evolution of hominids. e.g. increased brain size, spine shape, position of knee Cultural evolution is the changing of ideas held and actions carried out by societies and the transmission of these ideas through social learning from one generation to the next. e.g. the use of fire, agriculture, tools, weapons, religion, beliefs

59. D.3.10 Discuss the relative importance of genetic and cultural evolution in the recent evolution of humans. TOK Read this article: Are We Still Evolving? What do you think of the arguments for and against this proposition?

60. The cultural evolution has spanned millions of years in three major stages: the nomadic (hunting), agricultural (settled), and industrial ages. However, we have not changed biologically in any significant way. We could take a baby from 80,000 years ago, raise it in a modern environment and it would be indistinguishable from other humans in terms of intelligence and social capabilities. http://www.flickr.com/photos/wallyg/415498335/

61. Further information: Excellent site! BBC Website