volution commonalities in our growth and development. For example, most children can sit without support by months of age, stand with support by months and walk by one year. Once the underlying physical structure is sufficiently developed, proficiency in these behaviours requires adequate environment and little practice. However, special efforts to accelerate these behaviours do not help if the infant is maturationally not ready.
These processes seem to “unfold from within”: following an inner, genetically determined timetable that is characteristic of the species. Evolution refers to species-specific changes. Natural selection is an evolutionary process that favours individuals or a species that are best adapted to survive and reproduce. The evolutionary changes are passed from one generation to the next within a species.
Evolution proceeds at a very slow pace. Emergence of human beings from great apes took about million years. It has been estimated that the ‘Homo sapiens’ came into existence only about , years ago. influences such as winning an award or getting a good job.
People keep on changing with changing contexts. F ACTORS I NFLUENCING D EVELOPMENT Have you observed in your class that some of you have dark skin, others have light coloured skins, colour of your hair and eyes are different, some of you are tall, others short, some are quiet or sad while others are talkative or cheerful. People also differ with respect to intelligence, learning abilities, memory, and other psychological characteristics besides physical characteristics. Despite these variations, no one can be mistaken for any other species: we all are homo sapiens .
What causes us to be different from each other but at the same time more like each other? The answer lies in the interaction of heredity and environment. You have already learned in Chapter that the principles of heredity explain the mechanism for transmission of characteristics by every species from one generation to the next. We inherit genetic codes from our parents, which are in every cell of our body.
Our genetic codes are alike in one important way; they contain the human genetic code. It