This week I want to go back to evolution and examine one of the very momentous events that impacted on the development of humankind. Darwin, to the chagrin of many of his Victorian contemporaries, proposed that we all are the descendants of a prehominid species whose ancestry we share with the apes.
The event I refer to occurred about 5 million years ago in Africa. At that time in various places the forests were thinning. Consequently some of the inhabitants of the forests were forced to come out of the trees and live largely on the ground. The creature that evolved from these circumstances was the tiny Australopithecus. This forebear of ours appeared between 3 and 4 million years ago. Learning to live out of the trees, adopting a more upright posture and taking up residence in the grasslands where it survived and prospered, prepared it to be the progenitor of the human race. These little creatures probably used their upright position to establish a kind of cooperative life, sharing of child rearing and food which prior to then had been unknown.
Many believe that the main impact of learning to walk upright was the freeing of our fore limbs, which facilitated the construction and the use of tools. Scientists have speculated that it was this development that caused the rapid increase in the size of the brains of these hominids.
Homo habilis (“handy human”) descended from the australopithecines. They prospered between 2.3 to 1.3 million years ago. They were characterized by a larger brain, a more upright stance, and greater socialization. They were the first significant tool makers. The increasing use of tools improved their effectiveness at hunting and constructing shelter, both of which vastly improved their survival prospects.
The British born geneticist and evolutionary biologist J B S Haldane noted that change in the brain that occurred at this time was the fastest evolutionary transformation known. The growth in brain size over a period of just more than a million years caused it to double in volume. The trend continued with the next evolutionary leaps from homo habilis to homo erectus (“upright human”) to homo sapiens (“wise human”).
[Haldane was famous for the response he gave to some theologians who asked him what could be inferred about the mind of the Creator from the works of His Creation. Haldane reputedly responded “An inordinate fondness for beetles.” He was referring to the fact that over 400,000 species of beetle have been identified!]
Such was the rate of growth that hundreds of thousands of years ago our ancestors had brains of similar size to ours. Normally evolution cause organisms to be selected for the characteristics that help them adapt to the environment. What was the evolutionary advantage of a brain that had, in advance, the potential capacity to understand the laws of relativity and quantum mechanics, the capacity to launch rockets into outer space, master calculus and so on when it was lodged in the body of a being eking out existence in a hunter/gatherer society? This question continues to puzzle us.
It has been posited that the driving factor to walk upright might even have been the need to more effectively cool the growing brain. An upright hominid resulted in the head being a metre or more above the ground where the humidity was lower and there was more access to the breeze. As well the upright posture resulted in a smaller area being exposed to radiation from the sun. This is important because the brain uses a disproportionate amount of the body’s energy and must therefore dissipate considerable heat into the environment. This is evidenced by the fact that the concentration of sweat pores in the forehead is far higher than anywhere else in the body. And in facilitating this cooling process we became, over the eons, less hairy than the apes.
One of my favourite authors in the field of trying to understand consciousness and the functioning of the human mind is the University of California psychologist and researcher, Robert Ornstein. He has suggested that the increase in brain size might have had evolutionary advantages in the redundancy that they gave our ancestors as hunters. Human hunters often ran down their prey by driving them to exhaustion. If you are doing this in a tropical climate then heat stroke is a likely outcome which would result in the destruction of brain cells. Having surplus brain cells then would be an advantage.
But the development of human characteristics was not just due to the increased use of tools. Nature was confronted with a dilemma. Just as brains were expanding, hominids were learning how to walk. As a result of their bipedalism the structure of the human skeleton was being modified. One resultant outcome was that the birth canal in females was reduced in size. Humankind had to deal with a major problem in that the head size of babies was increasing because of the brain expansion at the very time that the birth canal was reducing, resulting in a growing peril for both mothers and babies.
Nature solved this dilemma by allowing human babies to be born in a more immature state than those of other animals. The flip-side to this of course is the fact that human children are far more vulnerable than those of other species and must be nurtured and protected longer whilst their brain and physical capacities develop. If a wildebeest gives birth on the Serengeti Plain and its calf is not up and mobile within hours it will more than likely be destined to be on the menu of a predator. It takes many years for our children to become in any way self-sufficient.
The rate of growth of the brain is kept to a minimum in the last months of pregnancy. After birth, however, it increases three fold in size in the first year. Consequently our children don’t come with so much of their behaviour “hard-wired” so to speak. This long period of maturation provides a fertile opportunity for social enculturation. This enables the “learnt” behaviour of humans to be a significant part of their psychological makeup.
Of all animals our brains have the most potential for post-natal development. It is instructive that, as research has shown, the capacity of such development is enhanced by the presence of love in the early care-givers. The potential of Humankind is optimised by the early intervention of love.
In our formative years, loving interaction with others optimises our developmental opportunities as human beings. Through the rest of our lives loving interactions and empathetic concern for the well-being of others contributes to the richness of our internal world and results in the promotion of our spiritual growth.
So it would seem that coming out of the trees and learning to walk were major factors in the creation of modern humans, enhancing their intelligence and probably facilitating access to consciousness in a way that differentiates us from other animals.
But it is not without its downsides.
Our spines were originally developed for walking on all fours and so this recent (in evolutionary terms) development has meant that we are not yet quite physically reconciled with our new posture. This partly explains the high incidence of back problems that we experience.
I would also suspect that being upright means that our hearts have to generate a higher blood pressure to circulate blood around our bodies. This is then likely to be a contributing factor towards heart disease, hypertension and strokes.
But surely not too big a price to pay for having the most sophisticated organ that the world has ever seen? Or am I being too big-headed?