Evolution

What is Evolution?

Evolution is the process by which inherited characteristics in a population change over time due to natural selection:

1. Organisms within the same species will all have different characteristics (phenotypes) due to their genetics. 
2. Some of these phenotypes might make certain individuals better adapted to their environment than others. For example, they may be better at acquiring food or camouflaging from predators.
3. Individuals with these advantageous traits are more likely to survive and successfully reproduce. This concept is called survival of the fittest.
4. Alleles that cause the advantageous traits will be passed on to the offspring .
5. Over time these advantageous characteristics will become more common in the population so the population has changed. 

If this process repeats enough times, populations may change so much that they form whole new species.

The theory of evolution states all species alive on earth today evolved from simple life forms over three billion years.

Theory of Evolution

The theory of evolution states that all species on earth today have evolved from simple life forms over three billion years. 

Charles Darwin is recognised for work on natural selection which he published in ‘On the Origin of Species‘ (1859).

• He gathered evidence during an around the world expedition.
• He did years of experimentation and discussions.
• He linked his findings to geological and fossil evidence. 

He found that individuals in a population show a wide range of variation for different characteristics. Some characteristics make the individual more suited to the environment and so are more likely to survive and successfully reproduce. The advantageous characteristics get passed on to their offspring.

Darwin’s theory was quite controversial at the time because it challenged the belief that God created all organisms on earth and there was also very little evidence to support the theory. Gradually, with the collection of more evidence and an improved understanding of genetic inheritance, the theory became accepted.

Other scientists, like Jean-Baptiste Lamarck, theorised that changes that happen through an organisms lifetime can be inherited by offspring but we know this is not often the case.

Speciation

Members of the same species can interbreed to produce fertile offspring.

Speciation is the formation of new species and can happen as a result of isolation and natural selection.

1. Populations of species are separated due to a physical barrier such as a river or mountain range.
2. Environmental conditions differ between the two areas.
3. Certain individuals in each population will be more adapted to the new environment.
4. Natural selection will cause individuals with the advantageous traits to survive, reproduce and pass on the advantageous genes.
5. This causes the advantageous traits to become more common in certain populations. 
6. Over time, the isolated populations will become so different that they will not be able to interbreed to produce fertile offspring and so will be two separate species.

Alfred Russel Wallace was one of the first people who studied speciation. He provided the foundation knowledge for future investigations which led to out current understanding of the concept. He worked along side Darwin and they published their findings in 1858 (a year before Darwin published ‘On the Origin of Species’). He is also well know for his work on warning colours in animals (particularly butterflies) which is used to support evolutionary theory. 

Extinction 

Extinction is when there are no remaining living individuals of a species.

Organisms can become extinct if they cannot adapt to a change quickly enough.

Factors that could cause extinction include:

• A new disease.
• A new predator.
• A new competitor.
• A change to the environment, i.e. climate change or habitat destruction.
• A catastrophic event, e.g. volcanic eruption or an asteroid hitting the earth.

Humans can also cause extinctions through hunting, habitat destruction or introduction of new species e.g. the extinction of the dodo.

When some species become extinct, others evolve more and thrive.