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 BiologyOption DD3 Human EvolutionJason de NysAll syllabus statements ©IBO 2007All images CC or public domain or link to original material.http://commons.wikimedia.org/wiki/File:LB1_skull.jpghttp://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 yearsIt is constantly being made in the atmosphere when cosmic rays cause neutrons to fuse with nitrogen nuclei and “kick out” protonsDecayFormation14C production is in equilibrium with its decay to 12CThe 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 50,000yhttp://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 yIt 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 100:0Over 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 decaySimulation 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 elapsedhttp://en.wikipedia.org/wiki/File:Halflife-sim.gif

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

7. ?.??3.420.130.7

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. humangibbongorillaGrasping pentadactyl limbshttp://www.flickr.com/photos/johnkay/5901639745/http://www.flickr.com/photos/shannonkringen/5466678956/http://www.flickr.com/photos/grendelkhan/1160017887/

10. Binocular Visionhttp://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 olfactionMonkeySquirrelvs.Doggiehttp://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. HumanBaboonGorillaGeneralised DentitionMoo Cownhttp://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 twistClavicle 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 timeLarger skull – relative to body sizeLarge brain – more complex, more foldsBetter visual acuity – more of the photoreceptors have their own sensory neuronsSocial 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.jpghttp://commons.wikimedia.org/wiki/File:Australopithecus_afarensis_reconstruction.JPGhttp://commons.wikimedia.org/wiki/File:Australopithecus_africanus_face1_(University_of_Zurich).JPGhttp://commons.wikimedia.org/wiki/File:Homo_habilis-KNM_ER_1813.jpghttp://commons.wikimedia.org/wiki/File:Broken_Hill_Skull_(Replica01).jpghttp://commons.wikimedia.org/wiki/File:Homo_sapiens_neanderthalensis.jpghttp://www.flickr.com/photos/53898309@N00/2211288333/Skulls not to scaleArdipithecusramidusAustralopithecus africanusAustralopithecus afarensisHomo erectusHomo habilisHomo neanderthalensisHomo sapiens

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

17. From the previous two slides you can see: enlargement of the brain case

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 sapiensPan troglodytes(chimpanzee)http://pandasthumb.org/archives/2006/09/fun-with-homini.htmlhttp://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.jpghttp://www.flickr.com/photos/cskk/2709688102/

23. Skeleton, locomotion and postureHuman 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 apesHuman pelvis broader

24. Neoteny,also called juvenilisation or pedomorphism, is the retention, by adults in a species, of traits previously seen only in juveniles. (Wikipedia)Some human characteristics thought to be a result of neoteny.Lack of body hair

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

32. Longer trunk relative to arms and legsD.3.6 State that, at various stages in hominid evolution, several species may have coexisted.

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. TOKRead the article on Wikipedia about Homo floresiensisDiscovered 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

37. D.3.7 Discuss the incompleteness of the fossil record and the resulting uncertainties about human evolution. It isn’t easy to create a collection of fossils that clearly show the change of species from one to another. Fossils rarely result when an animal dies for the following reasons: Decomposition is usually rapid; soft body parts are rarely fossilised

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

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

40. Only a tiny, tiny, tiny fraction of all of the fossils in existence have been found.Skulls and teeth are usually the parts of the ancestral hominids that survive to be fossilised and foundTherefore there is a lot of conjecture as to where they all fit in the family tree. Hypotheses are often overturned by new discoveries that rewrite the relationships between the species.http://www.flickr.com/photos/brentdanley/2205021283/

41. The large gaps in the human evolution fossil record are consistent with punctuated equilibriumThe 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. 1850http://en.wikipedia.org/wiki/Transitional_fossil

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