Evolution is the theory that all living things evolved from simple life forms more than 3 billion years ago.
There are two theories to explain evolution:
1. Lamarck’s theory was that organisms are able to adapt to the environment, and their offspring can be born with these ‘acquired’ adaptations. For example, if an elephant stretches its trunk longer and longer when its alive, the offspring of the elephant will be born with a longer trunk. This theory is WRONG.
2. Darwin’s theory was that organisms are born with the right adaptations, so as they survive and reproduce, their offspring are also born with the right adaptations. He called this the Theory of Natural Selection. This theory is CORRECT.
Darwin’s theory was not believed because, at that time, genetic theory had not been discovered, and there was insufficient evidence to support his theory.
Variation between species is caused by genetic mutation and variation leads to adaptation
Genetic mutation causes variation between species and this variation leads to adaptations.
An adaptation is a characteristic that helps the animal or plant survive the environment.
For example, different skin colour of peppered moths helps moths to camouflage and avoid predators.
For example, large-sized beaks helps finches (birds) eat large-sized seeds that grow on some islands.
Remember, don’t get confused:
The animal or plant does not adapt to its environment,
The animal or plant is born with the right adaptation so it survives
If the animal or plant is born with the wrong adaptation then it does not survive.
Survival of the fittest
Survival of the fittest describes how all organisms are competing to survive. They are competing for food, living space, mates and avoiding predators. Only those organisms born with the right adaptations have the best chance of surviving the environment.
Darwin’s Theory of Natural Selection
Natural Selection is the theory Darwin uses to explain evolution.
- Organisms are born with differences (variation) due to genetic mutation.
Only those organisms born with the right genetic mutation, causing the right adaptation, can survive the environment (Survival of the Fittest).
Those organisms that survive and reproduce pass on their genes to the next generation so more offspring will have the right adaptation.
Evolutionary relationships (evolutionary trees)
Evidence from fossils and genetic studies have shown how organisms have evolved from common ancestors.
These may be shown in diagrams called evolutionary trees.
For example, analysing the evolutionary tree for the great apes (see diagram below):
1. Humans (hominids) evolved around 6 million years ago.
2. Humans (hominids), chimpanzees and bonobos arose from a common ancestor that was present around 6 million years ago.
3. Gorillas evolved around 9 millions ago.
4. Orangutans evolved around 15 millions years ago.
5. Humans (hominids), bonobos, chimpanzees, gorillas, and orangutans all evolved from a common ancestor that was present around 15 million years ago.
6. The most distant evolutionary relative of the human (hominid) species is orangutan, however, the closest evolutionary relatives of human (hominid) species are bonobos and chimpanzees.
Wellcome Trust, Tree of Life video (David Attenborough) (click here)
Evolution explanation video
Candidates should use their skills, knowledge and understanding to:
■ interpret evidence relating to evolutionary theory
■ suggest reasons why Darwin’s theory of natural selection was only gradually accepted
■ identify the differences between Darwin’s theory of evolution and conflicting theories, such as that of Lamarck
■ suggest reasons for the different theories
■ understand how evolutionary trees (models) are used to represent the relationships between organisms
■ develop an understanding of the timescales involved in evolution.