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
4. 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 its 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
17. From the previous two slides you can see:

enlargement of the brain case

18. shortening of the face 19. loss of brow ridgesYou cant 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 bodys 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
24. Neoteny,also calledjuvenilisationorpedomorphism, 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 legs