B3.2 How has life on Earth evolved?

B3.2 How has life on Earth evolved?

Life on Earth began around 3500 million years ago. ALL life on Earth, including all life that is now extinct, evolved from very simple living things- so all organisms share a common ancestor. However there is variation between individuals of the same species and some of this variation is genetic so can be passed on to offspring.

Genetic variation is caused when changes called MUTATIONS take place in the genes. These changes are random and can be caused by background radiation and chemicals. MUTATIONS cause different proteins to be produces and this changes the function of the gene. If the mutations occur in the cells producing eggs in the ovaries and sperm in the testes, then the mutated genes may be passed on to the offspring. Sometimes the mutation causes new characteristics.

NATURAL SELECTION – The genetic variation between individuals in a species means that those with characteristics that improve their chances of survival in their physical environment are more likely to live to adulthood. When these individuals reproduce, they pass on the beneficial characteristics to their offspring.

SELECTIVE BREEDING – Where animals and plants with certain traits are deliberately mated together to produce offspring with certain desirable characteristics. This could be used to create new varieties of organisms or to increase the yield of animals and plants.

Differences between the two is that with selective breeding, it is humans who choose the desirable traits however with natural selection, it is the environment that determines the desirable traits.


The combined effects of the following can lead to the formation of new species:

  • Mutations
  • Natural selection
  • Environmental changes
  • Isolation – where individuals from one population are isolated from other populations so that they cannot meet to breed

This process is called EVOLUTION

Evidence for evolution is provided by:

  • The fossil record – fossils are the remains of plants or animals from thousands of years ago that are found in rock. Fossils indicate the history of species and can show the evolutionary changes in organisms over millions of years. The remains of the organisms are buried in the rock.
  • DNA organisms – similarities and differences in DNA can lead to the relationships being worked out between all life on Earth. Analysing the DNA of both living and fossilised specimens shows that there are similarities as well as differences. This can be used to chart the family tree of all life on Earth. The more shared genes organisms have, the more closely related they are.

Jean-Baptiste Lamarck was a scientist who proposed that the environment changed an organism. The organism then passed on the characteristic to their offspring, e.g. moles lived in the dark, so they lost their eyes as a result. This is called evolution through inheritance of acquired characteristics.

Charles Darwin devised a better explanation following many years of thought and collecting evidence. By collecting data, Darwin made the connection varieties, competition, the survival of the fittest and the passing on of desirable characteristics to the next generation.


Darwin’s theory was proven to be better because there was no evidence or scientific mechanism for Lamarck’s inheritance of acquired characteristics. The scientific community, having repeated Darwin’s experiments and peer reviewed his work accepts Darwin’s explanation for evolution over Lamarck’s.