D3 Human Evolution

Question 1

Outline the method of radiocarbon dating for dating rocks and fossils

Answer 1

• All living things are built from carbon-based organic matter
  
  • While alive, this carbon content exists as a mixture of two isotopes -12C(stable) and14C(radioactive) - maintained in constant proportions
  • When an organism dies, the proportion of radioactive14Cbegins to decrease as it is no longer being replaced from the environment
  • The proportion of14Cremaining can be used to identify the age of a sample
  • Carbon-14 analysis is only an effective means of dating for sample up to ~60,000 years of age as it has a half life of only 5,730 years

Question 2

Outline the method of potassium-argon dating for dating rocks and fossils

Answer 2

• Longer range dating can be accomplished by dating the rocks around a fossil to determine an age range (i.e. relative dating)
  
  • These dating techniques can only be undertaken on igneous rocks, not on the fossils themselves or the sedimentary rock in which they are found
  • 40K is released in lava from active volcanos and decays into40Ar with a half life of 1,300 million years
  • Using the time of the volcanic eruption as a zero time point, the age of the strata in which the fossil was found can be determined
  • As any40Ar would have been released during the eruption as a gas, levels of40Ar in the strata provide an indication of relative age

Question 3

Define half-life

Answer 3

The half life of a radioisotope is a measure of the time taken for the radioactivity to fall to half its original level

In other words, it is a measure of the time taken for half the atoms in a radioactive sample to decay

Question 4

Describe the major anatomical features that define humans as primates

Answer 4

• Forward facing eyes, giving stereoscopic vision
  
  • Large brain volume relative to body
  • Opposable thumbs capable of grip

Question 5

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

Answer 5

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Question 6

State that, at various stages in hominid evolution, several species may have coexisted

Answer 6

Several species of hominid may have co-existed at the same time:
• Homo habilismay have co-existed with various species ofAustralopithicus
• Homo neanderthalensislikely co-existed withHomo sapiens

Question 7

Discuss the incompleteness of the fossil record

Answer 7

• Fossilisation is an exceptionally rare occurrence that requires an unusual combination of special conditions
  
  • Most living things tend to decompose rapidly (or be scavenged) following death
  • Fossilisation tends to favour hard body parts (bone, teeth, shells, etc.) and exposed fossils will soon be weathered / destroyed
  • Only a small percentage of fossils have been discovered - fossilisation favours species that were long-lived and widespread

Question 8

Discuss uncertainties about human evolution resulting from the incompleteness of the fossil record

Answer 8

• Individual fossils may not be representative of species (e.g.Homo floresiensis- ‘Hobbit’ man)
  
  • Very few complete skeletons have been discovered, and so paleoanthropology is an inductive (data-poor) science
  • Many conclusions have been drawn on limited data and are frequently re-interpreted in the light of new discoveries

Question 9

Discuss the correlation between the change in diet and increase in brain size during hominid evolution

Answer 9

• A change in habitat in Africa ~2.5 million years ago may have prompted the emergence of Homo species from forest to savannah
  
  • This necessitated a change of diet to include meat (more protein), which increased the skull capacity and brain size of hominids
  • Improved diet quality provided energy to support greater brain function and learning capacity (positive correlation)
  • Activities resulting from improved cognition (such as group hunting and cooking food) enabled hominids to eat a wider variety of food

Question 10

Distinguish between genetic and cultural evolution

Answer 10

Genetic evolutioninvolves physical changes in the human genome which become inherited (passed on through reproduction). It involves the transfer of genes from one generation to the next (slow transfer).

Cultural evolutioninvolves changes in human thinking and can be passed on by communication/social interaction. It involves the transfer of ideas/information either within or across many generations (fast transfer).

Question 11

Discuss the relative importance of genetic and cultural evolution in the recent evolution of humans

Answer 11

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