How does the evolutionary perspective explain the biological basis of behaviour?

Evolution refers to gradual and orderly biological changes that result in a species from their pre-existing forms in response to the changing adaptional demands of their environment. Physiological as well as behavioural changes that occur due to the evolution process are so slow that they become visible after hundreds of generations. Modern human beings possess some features for several thousand years. Three such important features which differentiate them from their ancestors are - (i) A bigger and developed brain with increased capacity for cognitive behaviours (ii) Ability to walk upright on two legs (iii) A free hand with a workable opposing thumb.

Our behaviours are highly complex and more developed than those of other species because we have got a large and highly developed brain. Human brain development is evidenced by two facts. Firstly, the weight of the brain is about 2.35 per cent of the total body weight, and it is the highest among all species. Secondly, the human cerebrum is more evolved than other parts of the brain. These evolutions have resulted due to the influence of environmental demands.

Some behaviours play an obvious role in evolution. For example, the ability to find food, avoid predators, and defend one’s young are the objectives related to the survival of the organisms as well as their species. The biological and behavioural qualities, which are helpful in meeting these objectives, increase an organism’s ability to pass it on to the future generation through its genes. The environmental demands lead to biological and behavioural changes over a long period of time.

The autonomic nervous system governs activities which are normally not under direct control of individuals. The autonomic nervous system has two divisions - sympathetic division and parasympathetic division. The sympathetic division deals with emergencies when the action must be quick and powerful, such as in situations of fight or flight. During this period, the digestion stops, blood flows from internal organs to the muscles, and breathing rate, oxygen supply, heart rate.

The endocrine glands play a crucial role in our development and behaviour. Some of our behaviours are controlled by hormones secreted by different endocrine glands. The normal functioning of all hormones is crucial to our behavioural well-being. Without a balanced secretion of hormones, the body would be unable to maintain the state of internal equilibrium. Without the increased secretion of hormones during the times of stress, we would not be able to react effectively to potential dangers in our environment. Without the secretion of hormones at specific times in our lives, we would not be able to grow, mature and reproduce.

Cerebral cortex has four lobes. These are (i) Frontal lobe, (ii) Parietal lobe, (iii) Temporal lobe, (iv) Occipital lobe.

(i) Frontal lobe: It is mainly concerned with cognitive functions, such as attention, thinking, memory, learning, and reasoning. It also exserts inhibitory effects on autonomous and emotional responses.

(ii) Parietal lobe: It is mainly concerned with cutaneous sensations and their co-ordination with visual and auditory sensations.

(iii) Temporal lobe: This is primarily concerned with the processing of auditory information. This is the site of memory for symbolic sounds and words. Understanding of speech and written language depends on this lobe.

(iv) Occipital lobe: It is mainly concerned with visual information. Interpretation of visual impulses, memory for visual stimuli and colour visual orientation is performed by this lobe.

Information is transmitted from one place to another within the nervous system in the form of a neural impulse. A single neuron can carry a neural impulse upto a distance covered by the length of its axon. When the impulse is to be conducted to a distant part of the body, a number of neurons participate in the process. In this process, one neuron relays the information to a neighbouring neuron. The axon tip of a preceding neuron make functional connections or synapse with dendrites of the other neuron.