Some variation within a species is inherited, and some variation is due to the environment.

Inherited causes of variation

Variation in a characteristic that is a result of genetic inheritance from the parents is called inherited variation.

Each egg cell and each sperm cell contains half of the genetic informationneeded for an individual. When these join at fertilisation a new cell is formed with all the genetic information needed for an individual.

Environmental causes of variation

Characteristics of animal and plant species can be affected by factors such as climate, diet, accidents, culture and lifestyle. For example, if you eat too much you will become heavier, and if you eat too little you will become lighter. A plant in the shade of a big tree will will grow taller as it tries to reach more light.

Adaptation

Darwin's theory of evolution explains how species of living things have changed over geological time. The theory is supported by evidence from fossils and by the rapid changes that can be seen to occur in microorganisms such as antibiotic-resistant bacteria. Many species have become extinct in the past, and the extinction of species continues to happen.

E.g Polar bears are well adapted for survival in the Arctic. They have:

• a white appearance, as camouflage from prey on the snow and ice
• thick layers of fat and fur, for insulation against the cold
• a small surface area to volume ratio, to minimise heat loss
• a greasy coat, which sheds water after swimming.

Natural selection is known as survival of the fittest!

1)There is variation in a species

2) Sometimes this variation is an advantage

3) Therefore you're more likely to survive

4) You are more likely to breed

5) The variation is passed on

6) Over generations they inherit the advantage.