There appears to be a certain analogy between the development of human thought in general and the development of the language and thought of the individual human being through childhood and adolescence to adulthood.

This point was made by Engels in The Part Played by Labour in the Transition of Ape to Man:

For, just as the developmental history of the human embryo in the mother’s womb is only an abbreviated repetition of the history, extending over millions of years, of the bodily evolution of our animal ancestors, beginning from the worm, so the mental development of the human child is only a still more abbreviated repetition of the intellectual development of these same ancestors, at least of the later ones.[62]

The study of the development from embryo to adult is called ontogeny, whereas the study of evolutionary relationships between species is called phylogeny. Both are strangely linked together, but not as a crude mirror image. For instance, during its development in the womb, the human embryo resembles a fish, an amphibian, a mammal, and appears to pass through phases which recall the stages of animal evolution. All humans are alike in many respects, particularly the substances and structures of the brain. Chemically, anatomically and physiologically there is amazingly little variation. At conception, the fertilised ovum develops into two hollow balls of cells. The first recognised development takes place within eighteen days, as thickening where the balls touch becomes the neural groove. The forward part enlarges, later to develop into a brain. Other differentiation takes place which will become the eyes, nose and ears. The blood circulation and nervous systems are the first to function in embryo life, with the heartbeat commencing in the third week of conception.

The neural groove becomes a channel and then a tube. In time it will be transformed into the spinal cord. At the head end, swellings appear in the tube to form the forebrain, midbrain and hindbrain. Everything is set for the rapid development of the central nervous system. There is a qualitative leap in the rate of cell division approximating the final cellular structure. By the time the embryo is 13 mm long, the brain has developed into the five-vesicle brain. The stalks that form the optic nerves and eyes emerge. By the end of the third month, the cerebral cortex and cerebellum can be identified, as well as the thalamus and hypothalamus. With the fifth month the wrinkled cortex begins to take shape. All the essentials are developed by the ninth month, although further development will take place after birth. Even then, the weight of the brain is only about 350 grams, compared with 1,300 to 1,500 grams of an adult. It will be 50 per cent of its adult weight at six months, 60 per cent at a year, and 90 per cent at six years. By the age of ten, it would be 95 per cent of its adult weight. The rapid growth of the brain is reflected in the size of the head. The size of a baby’s head is large for its body compared to an adult. The brain of a newborn baby is closer than any other organ to its adult state of development. At birth the brain is 10 per cent of the entire body weight compared to only 2 per cent in the adult.

The physical structures of the brain (its biochemistry, cellular architecture and electrical circuitry) are modified by the effects of the brain’s response to the environment. Ideas and memories are encoded in the brain in terms of complex changes in the neural system. Thus, all the processes of the brain interact, to give rise to the unique phenomenon of consciousness – matter aware of itself. For Canadian psychologist Donald Hebb, the key lies in the synaptic junctions between two nerve cells, which remain the basis of today’s ideas. Particular sets of circuitry and firing patterns between the synapses may encode the memory, but it will not necessarily be localised to a single network of the brain. It can be encoded in both the hemispheres and many times over. The entire scope of the individual’s environment, especially in the early years of development, continuously leaves unique impressions on the brain processes and behaviour. “A variety of the most subtle changes in environment, especially during childhood,” says Rose, “can produce long-lasting changes in its chemistry and function.”

Without this dialectical interaction between brain and environment, then the individual’s development would simply be prescribed by the genetic code. The behaviour of individuals would be precoded and predictable from the beginning. However, the environment plays a decisive role in development. A changed set of circumstances can bring about a remarkable change in the individual.

  1. Engels, F. The Dialectics of Nature, p. 241.