Biological Approach:
The Biological approach is shaped by internal/physical factors. Biological psychologists to study mental processes and behaviour apply the principles of body: genes. The genes adopt behaviour to the environment; our intelligence depends on the genetic make-up. The assumptions of the biological approach are: Genes influence production of hormones, hormones influence the brain structure and the brain structure influences our behaviour.
The nucleus (cell in the human body within the exception of red blood cell) has 46 structures called chromosomes which are made up of DNA. Each DNA carries genes. The research on the genetic influence of behaviour has been conducted in mice because they have shorter gestation period. For example Bock and Goode in 1996 carried out a research on mice that were reared alone and they showed a strong tendency to attack other male mice. These mice were not taught to be aggressive, that is from their parents-genes.
Psychologists can manipulate genes in order to measure the effects on behaviour. They use genetic mapping, genetic engineering and selective breeding (the artificial selection of male and female animals. These animals are then put breed and produce offspring).
Darwin in 1859 proved that all living things have evolved over time. He showed scientific evidence how random physical and behaviour changes to a species.
There are many examples of evolutionary behaviour. For example sexual selection- male species display traits such as mating calls, brightly coloured plumage. In humans the evolutionary behaviour such as the rooting reflex- New born babies will turn their heads towards anything that touches their cheek.

Strengths:
-Scientific and experimental methods in the investigations.
- Strong argument for the nature-nurture debate.
- Many useful applications- drugs that alleviate disorders.

Limitations:
-Reductionist. It explains the behaviour in terms of the actions of nerves or chemicals.
-The approach is over-simplistic. Don’t appreciate environmental factors on our behaviour.
- Ethical issues- genetic mapping.

Behaviourist approach:
John Watson revolutionised psychology and established behaviourism. This approach states that people are born as a blank slate and their behaviour is learnt from the environment. Behaviour psychologists to be scientific have to only study overt behaviour, and all behaviour is learned through direct experience.
There are general laws of learning:
-classical conditioning (associating instinctive reflexes with new stimuli)
-operant conditioning (associating voluntary responses with consequences-Reinforcement/punishment.

There was a research studies carried out by Ivan Pavlov. He was a Russian psychologist who was researching the digestive system of dog. In the research he rang a bell and at the same time he presented the food to the dog. The dog was salivating as a reflex response. After certain amount of trials he realized that he doesn’t have to show the food to the dog because the dog was salivating just to the sound of bell.
There are 2 types of reinforcement:
Positive reinforcement which provides a feeling of satisfaction.
Negative reinforcement involves the removal of an unpleasant experience.

Unconditioned Stimulus- A stimulus that elicits a response without conditioning.
Unconditioned Response- An automatic response elicited by the unconditioned stimulus.
Conditioned Stimulus- A neutral stimulus that when paired with an unconditioned stimulus elicits a similar response
Conditioned Response- A response that is learned by paring the originally neutral conditioned stimulus with the unconditioned stimulus.

Strengths:
Behaviourists use many experimental methods of research
They provide strong arguments for the nurture side
The approach provided a number of practical applications and techniques to shape behaviour

Limitations:
The approach ignores