IB Biology Option D D3 Human Evolution Jason de Nys 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.

D.3.1 Outline the method for dating rocks and fossils using radioisotopes, with reference to 14 C and 40 K. 14 C 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 14 C production is in equilibrium with its decay to 12 C The 14 C is incorporated in carbon dioxide which is then taken up by plants. In the end all living things have the same ratio of 14 C to 12 C When an organism dies it no longer takes in 14 C. So over time the ratio of 14 C to 12 C changes. This is measurable and can be used to estimate age. The limit for accurate determination of age is about 50,000y Formation Decay

40 K is an isotope with a half life of 1.3 X 10 9 y It decays to 40 Ar. When 40 K is released from a volcano in lava all of the argon gas is driven off. So brand new rocks effectively have a ratio 40 K: 40 Ar of 100:0 Over time the lava may be weathered and eroded and incorporated into sedimentary rocks. The measured ratio of 40 K to 40 Ar can be used to date rocks over one million years old with an accuracy of around years

D.3.2 Define half-life. 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 The time it takes for half of a radioactive isotope to decay

What is the half life for each of the isotopes represented by these curves?

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

D.3.4 Describe the major anatomical features that define humans as primates human gibbon gorilla Grasping pentadactyl limbs

Binocular Vision

Reduced snout leading to reduced olfaction vs. Squirrel Doggie Monkey Human

Generalised Dentition Human Baboon Gorilla Moo Cown

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) Greater Parental care, Prolonged infancy - 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

D.3.5 Outline the trends illustrated by the fossils of Ardipithecus ramidus, Australopithecus including A. afarensis and A. africanus, and Homo including H. habilis, H. erectus, H. neanderthalensis and H. sapiens.

Ardipithecus ramidus Australopithecus africanus Australopithecus afarensis Homo habilis Homo erectus Homo neanderthalensis Homo sapiens Skulls not to scale

1. Gorilla 2. Australopithecine 3. Homo erectus 4. Neanderthal (La-Chapelle-au-Seine) 5. Steinheim Skull 6. Modern human

From the previous two slides you can see: enlargement of the brain case shortening of the face loss of brow ridges You 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.

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

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

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

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 Small teeth and reduced numbers of teeth Prolonged growth period Long life span Flat face and thin skull bones Lactase production in adults Epicanthic eye fold Small nose Longer trunk relative to arms and legs

Note that according to this interpretation of the fossil record Homo sapiens is not descended from Homo erectus or Homo neanderthalensis. However, some postulate that Homo sapiens may have hybridised with Homo neanderthalenis. This could have contributed to the disappearance of the neanderthals in much the same way that indigenous animals like dingos are in danger of extinction due to breeding with domestic dogs.

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 Scavengers usually break up skeletons and even chew up bones The conditions have to be just right for fossilisation to occur. 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 found Therefore 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.

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

D.3.8 Discuss the correlation between the change in diet and increase in brain size during hominid evolution. The benefits of a bigger brain include: More complex tools Mastery of fire Cooking Wamth Protection Greater behavioural flexibility (less reliance on instinct and better able to learn and pass on knowledge necessary to adapt to an environment)

The cost of having a big brain: Longer gestation period Years of development before young can look after themselves Much more brain development occurs post birth that for any other animal In 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.

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

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. The cultural evolution has spanned millions of years in three major stages: the nomadic (hunting), agricultural (settled), and industrial ages.

BBC Website Further information: Excellent site!