By: Dr Irengbam Mohendra singh
A mega drought occurred in Africa 5 million years ago and that forced evolutionary change on the apes, ancestral to both humans and chimps.
The population of these ancestor apes was between 50,000 and 100,000, according to genetic calculations. Times then were hard, with dwindling fruit-bearing trees and a shrinking habitat of forests. Generation after generation began to produce offspring who were more and more capable of adapting to the new changing environment.
Two sets of offspring survived. One continued to manage in the sparse forest as it continued to cling to the same old habit. It continued to create the lineage of chimpanzee.
The other managed to venture outside the forest while clinging to the trees at other times. Having learnt to survive on the ground, it managed to walk on two feet (bipedal apes), an evolution towards becoming human. The first walking apes, Astralopithecines, appeared in the fossil record 4.4 million years ago.
According to archaeologists, by 100,000 years ago the human branch of the apes had developed into humans who were anatomically similar to people of today but not behaviourally. By 50,000 years ago our ancestors still in their homeland of
African Northeast began to show signs of modern behaviour.
There are three hypotheses of the origin, evolution and migration of modern humans.
1. Out of Africa model (OA) by Christopher Stringer and Peter Andrews.
2. Multiregional model (MR) by Milford Wolpoff et al.
3. Prehistoric human gene migration (seeking an explanation adaptable
between OA and MR models).
In the 1990s from archaeological evidence, OA or RAO (Recent African origin)
has lent a strong support.
Scientists interested in human prehistory and evolution have made studies by using DNA analysis, of ‘archaic humans’ known as Homo Neanderthals (from a fossil found in the Neanderthal valley in Germany in 1857) who populated Europe and the Near East; and Homo erectus (standing man) who settled in parts of Asia.
Human evolution is characterised by a number of changes such as morphological, developmental, physiological and behavioural, which have taken place since the division between the last common ancestor of humans and the chimpanzees, 5 million years ago after a severe drought in Africa.
Then, 3 to 2 million years ago, there was another long period of cool, dry climate in which Africa’s forest diminished further. Another species called Homo habilis emerged. It retained its ape-like body form. They began to eat meat.
Meat eating allowed smaller gut to grow bigger (that’s how the appendix became a vestige) and provided extra nutrition to develop a bigger brain. The brain requires high quality nutrition that meat but not vegetarian food can provide
About 1.8 million years ago, during a warm interlude before the Pleistocene Ice Age
early humans left Africa in one or more groups. These archaic humans migrated to different parts of the world and followed their own evolutionary paths.
In the course of time they became extinct species known as Homo Neanderthals who settled in Europe and intermittently, parts of the Near East at about 50,000 years ago in the Pleistocene Ice Age. Homo erectus had reached Asia about 1 million years ago and settled in East Asia.
The first Homo sapiens came out of Africa and dispersed across the world 50,000 years ago, at a time when the northern latitudes of Europe and Asia were covered by sheets of ice. From northeast Africa they crossed the Red Sea to Arabia and travelled until they reached India where they split into two groups, each going separate ways.
One group expanded along the coastlines of southern Asia until they reached the foundered continent of Sahul (now Australia, New Guinea and Tasmania, all connected then as a land mass) some 46 thousand years ago.
Another group travelled along the land route, northeast from India and when they reached Europe slowly evicted the Neanderthals from their ancient homeland.
The evolutionary changes continued by events such as extremes of temperature, a variety of diseases, and cultural innovations. The anatomically modern humans were bereft of modern human behaviour and lacked the faculty of speech.
Modern humans in the past 20,000 years since their ancestors left Africa had occupied most of the world and were dependant on hunting and gathering for their existence. (Hunter-gatherers).
The human genome has provided geneticists with the means to trace the journey of the first emigrants from Africa by studying the male-producing Y chromosome and the maternal mitochondrial DNA (mtDNA).
The recent knowledge of human migration comes from studies of mtDNA from the existing population. The most ancient human mitochondrial lineages are L1, L2 and L3 specific for Africa. L3’s daughter lineages (northeast African) are M and N that left Africa to colonize temperate zones. Lineage M is of particular interest in tracking the exodus of humans from Africa to India and Manipur.
The genes change in human evolution. Genes are strings of DNA molecules that embody the information to make proteins. Proteins are working parts of the living cell. Each gene comes in a variety of different versions known as alleles.
Alleles pass at random onto the next generation and the next and so on until it becomes ‘fixed’ or ‘universal’. That is when the population is said to have gone through evolutionary change. Thus evolution is the change in allele frequency over time in a population of organisms.
The genes are replicators. Everyone carries about half of their father’s genes and half of their mother’s. The other halves are discarded along with the genes they contain.
All genes look alike but differ only in their effects on the embryo in the future generations. A phenotype is a term used to the effect of a modified gene. For instance: the green eyes, pale skin, a snubbed Meitei nose, or the different features between Meiteis and Tangkhuls.
The existence of different human races such as Negroid, Mongoloid and Caucasian is more phenotypic evidence of evolution due to genetic differentiation. It is believed that the first humans who reached Europe 45,000 years ago would have retained their black skin and
other African features.
The variety of languages, different colours and different physical features of humans we have today are phenotypic evidence of evolution.
During the Last Ice Age about 20,000 years ago, a shift to a more European phenotype had occurred (Holiday 1997). Later changes occurred by about 11,000 years ago to European skin colour, eye colour, and hair colour through allelic changes.
Whitening of the skin through allelic changes at the AIM1 gene occurred at about 11,000 years ago (Soejima et al, 2005). So was the diversification of eye colour alleles at the OCA2 gene (Voight et al, 2005).The diversification of the hair colour alleles at MC1R gene has yet to be dated.
Geneticists believe that the changes were driven by adaptation to the natural environment and by intense sexual competition for mates, especially female-female competition for men, who were in short supply because of their long hunting distances (Frost, 2006).
The existence of different human races such as Mongoloid (Meitei), Negroid and Caucasian is more phenotypic evidence of evolution due to genetic differentiation.
There is no definite evidence for the Mongoloid anatomical change in the Natural Selection Theory. The current hypothesis is that the evolution to the Mongoloids emerged by genetic ‘drift.’ It means a random fluctuation in gene frequencies that occur between generations. It is a revolutionary change rather than evolutionary.
The first use of the term ‘Mongoloid race’ by a German, Christopher Meiners who classified human population into two races: Caucasian, and Mongolian – which consisted everyone else.
Biologists have long theorised that the Mongoloid features occurred during the end of the Last Glacial Maximum as an adaptation to the cold, 20,000 years ago while the Mongoloid skull would have developed by chance alone. The pale skin, the epicanthic folds of the eyes and stockier body are all adaptations for survival in the cold.
Marta Mirazon, the physical anthropologist says: one archaeological data at least confirms that humans from the Mongoloid race resided in North-East during the Palaeolithic era. It is estimated that it was at the end of Last Glacial Maximum, 20,000 years ago that our human ancestors began to settle down in East Asia before the invention of agriculture.
During the late Last Ice Age about 25,000- 20,000 years ago, anatomical change from the original dark African ancestors to the Mongolic phenotype occurred as did to the Meiteis in Manipur, because of ‘drift’ or by Natural selection, as adaptation to cold. The Meiteis were a small population and thus favourable to the force of ‘drift’
As natural selection acts solely by accumulating slight, successive, favourable variations (Darwin), the Meiteis, though having some phenotypic similarities to the other Mongoloid tribal people of Manipur and outside, have characteristics that are distinguishable from them by their deep- rooted linguistic, cultural and behavioural history, intrinsic only to them.
The writer is based in the UK