Introduction:

Humanity has passed through three major evolutionary phases - hunter gatherer , agricultural and technological . It is difficult to generalise on human lifestyles as adaptation to the environment is a continual, cultural and learned process. Instead of genetic adaptation, cultural adaptation has been important. Physical changes are small. Forest dwellers tend to be small, with a light muscular frame (Beazley, 1990). Eastern Mediterranean hunter gatherers of 30,000 to 9,000 years ago stood at five feet ten inches. Agriculturalists of 5,000 to 3,000 years ago, from the same region, only average five foot three inches (Kates, 1994). The American average in the industrial society of today is five foot eight inches. Evidence suggests that both the size and robustness of humans, and their brain volume has decreased over the last 10,000 years or so (Sci. Am, early 1995). For a very detailed history of the past 20,000 years refer to Mithen's (2003) 600 page book.
The traditional classification of human social evolution is into pre-history and recordered history. The latter follows the invention of writing and therefore written historical records. Pre-history is broken down onto 3 periods , according to the materiel used for making tools:
The Stone Age (50,000 BC to 4000 BC),
The Bronze Age (4000 to 2000 BC), and
The Iron Age (1500 BC onwards).
Some texts will explain that the Old Stone Age (the Paleolithic Age (50000 to 12000 BC) ) is the Age of food-gatherers, while the New Stone Age (the New Stone Age or the Neolithic Age (12000 to 4000 BC)) is referred to as the Age of food producers. This puts the Bronze age onwards as the Age of civilization, starting towards the end of the Neolithic Age. In the below discussion, I will look at three major lifestyle groupings:
Hunter gatherer,
Agriculture and
Technological civilisation.
The third is a complex grouping. Civilization requires, or may be defined by, settlement in definite territories, the building of towns and cities, the evolution of defined systems of government and the development of trade and commerce. This social system has and does exist together with the first two.
Firstly, I will delve briefly into the genetic record of our early history.
Genetic History: of modern man:
Some nuclear DNA sequences (including Y-chromosome data) and mtDNA indicate that modern humans originated and migrated relatively recently from a subset of the African population, putting Africa as the home of modern humanity. A study of human Y-chromosome variation in a worldwide sample of over 1,000 men determined that Africans and non-African males shared a common ancestor 59,000 years ago and that the non-African branch of humanity left Africa about 44,000 years ago. Such time estimates are based on the molecular clock hypothesis . Y-chromosome studies tend to misinterpret demographic events related to the origin and spread of populations, underestimating the age of those events. Mike Hammer (1995) at the University of Arizona, sequenced 2,400 bases in the same Y chromosome region from 16 ethnically diverse humans and four chimpanzees, and dated the common ancestral human Y chromosome at 188,000 years with a 95 percent confidence interval from 51,000 to 411,000 years. Other data shows that Africans and non-Africans split about 156,000 years ago (Underhill, et al, 2000), (Ingman, 2000). Within Africa the oldest modern human fossil is just less than 160,000 years old and represented by Homo sapiens idaltu.
Modern humans arose from a single evolutionary event, but our racial diversity illustrates subsequent multiple evolutionary events involving differential survival of populations, geographic range expansions, and migrations. A study of the male Y-chromosome has provided evidence of successful migrations from Africa by different human populations at different times (Underhill, et al. 2001). Underhill's team identified 10 haplogroups (using 131 different haplotypes); unique genetic groupings that could be used to study modern human racial distributions. Using 1000 human samples representing current racial distributions, they established a frequency distribution for the 10 haplogroups. They were able to trace a common African heritage and suggest some population subdivisions, gene flow episodes and colonization events. Their study showed an overall pattern of group differentiation and movement across the world, suggesting population expansions and genetic drift processes that would be expected over tens of thousands of years. This work has laid the foundation for a clearer understanding of our recent human history through the new science of phylogeography.
The two most diverse (and therefore more ancient) groupings (I & II) are found in Africa at low frequencies amongst some Khoisan and South African Bantu individuals, central African Pygmies, and lineages in Sudan, Ethiopia and Mali. A single Sardinian was in Group I and there was an Group II from Pakistan. The genetic information suggests an early diversification, dispersal and widespread distribution of human populations within Africa. Palaeoanthropological records suggest that this occurred during an interglacial 130,000 to 90,000 years ago. This is supported by faunal evidence, showing the presence of modern humans and east African animal species in the Middle East at this time (Underhill, et al. 2001).
Outside of Africa, there is evidence for the early formation of a non-African grouping, represented today by the Australians, New Guineans, southeast Asians, Japanese and central Asians. All Y-chromosomes that are not exclusively African contain an identifying mutation, that originated from one of the two African groups, and evolved into three distinct sub-clusters, representing the deepest structuring of Y-chromosome diversity outside Africa. Palaeoclimatic records suggest an onset of glacial climates 70,000 years ago, accompanied by the fragmentation of African environments. This isolated both northwest and northeastern most Africa from each other and the south. Isolation allowed African populations to evolve the variation later exported out of Africa more than once through multiple dispersals of different African groups. The current diversity found outside Africa is therefore a magnification of a process of diversification within Africa 90,000 to 50,000 years ago. Underhill's genetic study of the Y-chromosome shows further that populations not only trace their ancestry to Africa, but that the descendants replaced archaic human Y chromosomes in Eurasia (Underhill, 2000). The last common ancestor of all non-African human Y-chromosomes, is estimated to be about 40,000 years (31,000-79,000) ago. Numerous Y-chromosome populations have been identified outside of Africa, but their clear definition requires more data. One mutation group alone has split into six Y-chromosome populations. Today there are very distinct Y-chromosome distribution groups requiring further study.
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