Chapter 11: The Origin and Dispersal of Modern Humans
The human origin study cuts across many disciplines. It borrows evidence and data from anatomy, genetics, geology, and archeology. Three models are used to describe how modern humans have come to exist in the current states dating back to about 200,000 years. These models are: out of Africa model also (complete replacement), the multiregional model and the assimilation (partial replacement) model.
According to the complete replacement method, the modern humans in about 200,000 years ago originated from Africa, from where they spread to the other regions of the world. They replaced the Homo erectus descendants in Asia and also the Neanderthals living in Europe. The model is supported by the remains of the oldest modern humans found in Africa and the presence of two anatomically different lineages of hominin in each of the world regions. The evidence gives the model overwhelming support. The Multiregional model suggests that the modern humans came from Asia, Africa, and Europe and they evolved separately in their geographic locations. Also, there was the occurrence of some gene flow.
The Partial Replacement Model is a combination of both the Complete and Partial Replacement Models. It states that modern humans indeed originated from Africa, but they moved to the rest of the world where they interbred with the indigenous populations giving rise to one human species with regional variation.
The modern humans originated from Africa. They diverged from East Africa and then spread to Asia and also to Oceania. Ten thousand years later they further migrated to the Eurasian plate and Europe later to America. From these migrations, new populations were established by a minute number of the initial large population. This Founder effect is due to loss of genetic variations in the community.
Chapter 12: Human Variation and Adaptation
There are three levels of adaptation: acclimatization is a physiological change that occurs as a reaction to environmental change. The process is short-term and includes the increase in the number of red blood cells in organisms existing in higher altitudes. When an organism is exposed to environmental stress for a certain amount of time, they develop beneficial changes. This process is known as adaptability, and an example is increased bone density after intensive exercise. Genetic adaptation involves variations in chemical structure and composition of an organism to fit into a habitat. The changes take a lot of time to be achieved and are permanent. Lactose tolerance is an example of gene adaptation.
The race is not considered in modern humans since it is only a political, cultural and economic concept used in the society but lacks any biological idea. The idea is therefore regarded as sociological (Jurmain, 316). Despite the different blood groups, this cannot be used to divide humans into groups since it is not applicable in selecting mates and the variation is due to other factors away from social discrimination.
Works Cited
Jurmain, Robert. Essentials of physical anthropology. Nelson Education, 2016.
