Option D.3 – Human Evolution

Option D.3 – Human Evolution

D.3.1 – Outline the method for dating rocks and fossils using radioisotopes, with reference to 14C and 40K

Radioisotopes are used to determine the age of rocks containing fossils. The age is determined by analysing how much the isotope has decayed.

Carbon-14 (14C) and Potassium-40 (40K) dating, the age in half-lives can be deduced from the decay curve.

14C has a half-life of 5730 years, so it can only give accurate measurements for samples that are 1000-100,000 years old. The percentage of 14C isotopes remaining is measured.

40K has a half-life of 1250 million years, so it is used for dating samples older than 100,000 years. The proportion of parent isotope 40K is compared to the daughter isotope 40Ar.

D.3.2 – Define half-life

The time taken for the radioactivity to fall to half of its original level.


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

See D.3.1

D.3.4 – Describe the major anatomical features that define humans as primates

Primates include apes, lemurs, tarsiers and monkeys. The anatomical features include:

  • Grasping limbs – long fingers and separate opposable thumbs.
  • Mobile arms – shoulder joints allowing movement in three planes, bones of the shoulder joint girdle allowing weight to be transferred via the arms.
  • Stereoscopic vision – forward facing eyes on a flattened face, giving overlapping fields of view
  • Skull modified for upright posture

The similarities make it clear that humans evolved from other primate species. D.3.5 – Outline the trends illustrated by the fossils of Ardipithecus ramidus,

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.

The Hominidae family includes humans and other bipedal species. All other species in the Hominidae family are now extinct. In the past, several Hominidae species coexisted, including Homo sapiens and neanderthalensis. Fossils of hominids show very clear trends: increasing adaptation to bipedalism and increasing brain size in relation to body size. Ardipithecus fossils were found

Ardipithecus fossils were found in Ethiopia. Australopithecus and Homo habilis fossils were found in Southern or Eastern Africa. Homo erectus fossils were found in Eastern Africa and Asia. Homo neanderthalensis fossils were found in Europe and Homo sapiens fossils in many parts of the world.


The Ardipithecus ramidus from 4.4 million years ago only has fragments of skull that have been found. They seem to be an intermediate species between chimpanzees and Australopithecus. This is due to:

  • Smaller incisors than chimps
  • Blunt canines that project less than chimps
  • Small numbers of large molars
  • Foramen magnum further forward than in apes, suggesting that it was partially bipedal

D.3.6 – State that, at various stages in hominid evolution, several species may have coexisted

An example is H. neanderthalensis and H. sapiens, which seemed to coexist in Europe for a time.

D.3.7 – Discuss the incompleteness of the fossil record and the resulting uncertainties about human evolution

The fossil record provides much of our understanding of human evolution. However, there are many gaps in the record, which is normal for all organisms. Decomposition is much more likely to occur than fossilisation.

The gaps in the record mean that we cannot fully clarify the relationships between different hominid species. Sometimes, the discovery of new fossils can lead to major changes in the theories of human evolution and origin.

For example, a new Australopithecus species was discovered which has characteristics between Australopithecus ramidus and Australopithecus afarensis, yet dating shows that the three species did not coexist but form an evolutionary lineage. Of course, the details of the theory are still disputed.

D.3.8 – Discuss the correlation between the change in diet and increase in brain size during hominid evolution

The early hominids – Australopithecus – had a similar brain-body size ratio to apes. Their powerful jaws and teeth also indicate a vegetarian diet.

Climate change in Africa about 2.5 million years ago led to cooler and drier weather. As such, forest habitats became savannah grassland and prompted the evolution of the first Homo species. Their diet changed to involve using tools to hunt and kill large animals for meat.

With the change in diet came a change in brain size. Homo species experienced continued rapid brain growth after birth. The change may be due to:

  • Eating meat increases the supply of protein, fat and energy making it possible to grow larger brains.
  • Catching and killing prey is more difficult that obtaining plant food, so natural selection would favour larger brains and higher intelligence.

D.3.9 – Distinguish between genetic and cultural evolution

With larger brains, Homo sapiens and other Homo species were capable of learning much more. As such, language, hunting techniques, tool-making skills, methods of agriculture, religion, art and behaviour could be passed on during childhood and even adulthood.

Those things make up the culture of a group.

Since new methods, invention and customs could be passed on to the next generation, it is known as cultural evolution and is different from the evolution that involves natural selection of inherited differences: genetic evolution.

Cultural evolution does not involve changes in allele frequency in the gene pool. Changes due to cultural evolution can take effect in one human lifetime, rather than the many generations needed for genetic evolution. Cultural evolution is the characteristics inherited throughout life (nurture) whereas genetic evolution is of inherited characteristics (nature).

D.3.10 – Discuss the relative importance of genetic and cultural evolution in the recent evolution of humans

Cultural evolution has been responsible for most of the changes in the lives of humans in the last few thousand years. In that same time frame, genetic evolution could not cause much change.

Further, cultural evolution like medicine has reduced natural selection between genetic types, as consequently genetic evolution.