Chapter Six: Population Genetics
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This is a research work is based on the book Human Genetics: Concepts and Applications by Ricki Lewis. The research concentrated on Population Genetics chapter with the main focus being Human Ancestry. This chapter discusses the earliest human ancestors, their evolutions and relationship to the modern man.
Human ancestry has always been an intriguing subject, from the creation theory, the evolution theory to the myths held by every cultural community about people’s origin. No satisfactory answer has yet been found to explain exhaustively the origin of man and in particular his uniqueness from other species. In the book Human Genetics Concepts, Ricki Lewis tries to explain the origin of the current intelligent man as evidenced by the genetic and genomic evidences of evolution. Lewis gives a coherent and vivid explanation of every stage in the evolution. The different accounts of evolution are well presented making the book both informative and interesting. The book starts with an interesting remark; that though humans are one of their kind, this might not have always been so. This creates interest to inquire what these circumstances were that led to just us being of our own kind presently.
In his book, Lewis covers the topic of human evolution through division into different subchapters each having its own area of coverage. The first subtopic covers on the origin of humans. It is in this subchapter that the author explores the early hominids and hominins. The writer asserts that the first human like beings may have had come into existence during the period Pleistocene. Aegeptopithecus was the first monkey like animal to appear 30-40 million years ago. The first hominids lived in Africa about 22-32 million years ago. Other apes continued to appear with time but had little relation to human.
The Australopithecus replaced Aegeptopithecus and were the next human ancestors to appear. Their features were more ape-like than they resembled the humans. The oldest of these species is recorded to be 4.1 million years old. End of Australopithecus reign paved the way for the earliest relatives of man. The genus Homo. The earliest recorded fossil of Homos dates about 2.5 years ago. The homo species were more advanced and used tools. There comprised of different species as time elapsed and as civilization crept in. They included the Homo habilis; he could use tools and dwelled in caves. Homo erectus soon followed in the Paleolithic Age. These species saw the greatest development towards civilization. Studies of their fossils evidence indicate they used fire, exercised social organization, cooperation, and used tools. These species lived through to about 28000-24000 years ago in form of the Neanderthals. Competition form smarter and more archaic humans led to the decline of the Neanderthals. They were the closest relation to the human in terms of body structure. The next group focused in this book is the modern man. The modern man lived in caves, could use symbols as a form of communication and extended to cover Europe and the Middle East. These were the direct ancestors of humans as known today.
Further, the book explores more support for the evolution of humans. The author argues ‘fossils paint an incomplete picture of the past because they are scarce and only certain parts of organisms were preserved’. Regards this, the book explores further support and information on evolution from life molecules. In this study, the DNA and amino acids sequences are compared; the more closely they resemble each other, this is used as an indicator of related or closely shared ancestor.
Human beings have unique traits compared to other animals such as huge brain capacity; they use spoken language and other features such as opposable thumbs. These traits set them apart from the other animals. Natural selection played a huge role in human’s loss of hair; the chimpanzees have retained these hairs. Differences in genes between primates are reasons for their behavioral, physical and all their major differences. Genes in human differentiating human and chimps appear few, but Mendelian disorders tend to implicate them. The author further claims gene expressions, and not genome sequence, is the reason for the different behaviors between chimps and humans despite their huge similarity.
In genome consideration, it is found that human’s genome is complexly organized. These complexities are vital for development of highly complex organs. The author has further presented the factors that make humans human. The ability to use tools, which started from earliest human forms, sets them aside. The most significant difference between humans and other animals is their big brain capacity and the brain itself. A mutation of a gene in early humans prevented the production of type of muscles. This mutation exhibits in all humans but lacks in the chimps and accounts for the differences in brain sizes of the animals. Cognition, walking, sense of smell are other unique characteristics that modern humans demonstrate. Analysis of the human brain itself shows signs of replication. This is evidenced by repetitions of many DNA sequences in humans.
Another important aspect in research of ancient human’s fossils is the comparison of chromosomes. The book contends that similar chromosome banding patterns may be indicators of evolutionary matches. The human chromosome banding are found to closely resemble those of primates. Comparison of proteins is also another avenue that researchers have used to establish relationships of current life forms to ancient ones.
In addition measures in research of human relationship with the past, the need to estimate the time these DNA sequences that they diverged to the present differences. Molecular clocks have been extensively used to determine the time of divergence of these animals. This technology has been especially useful in sequencing the Neanderthal man fossils. Gene variants on the fossils have indicated a possibility that he could vocalize. It has also been that a gene mutation gave them a characteristic pale skin and red hair.
Towards the end of the chapter, the writer presents an interesting view of a mitochondrial Eve. This is a theoretical belief that the ancestry of human beings started somewhere in a Africa and from a single woman. This occurred about 200000 years ago when Homo erectus evolved to Homo sapiens in Africa. With time, this population expanded and at about 56000 years ago, the population migrated out of Africa. The book, in the explaining the populating of the world establishes that people spread across Eurasia and Siberia about 40000 years ago. A bottleneck population affected Beringia between 23000-19000 years ago, only 1000 surviving the journey from Siberia. These people settled in America after the first ice age and comprise the Native Americans today. This is the process that populated the whole world as evidenced by mtDNA mutations and current diversity. This book only quotes only this evidence for the populating of the whole world. It does not dwell on explaining the major causes of different cultural, the evolution of different languages and other characteristic differences that exist between races, ethnicities and people in different locations of the world. The fact that the whole population evolved from one Mitochondrial Eve, then the differences that exist ought to be fully explained.
This chapter touches the major evolution stages that led to the existence of the current man. It also explains major causes that cause the existence of differences among humans and animals. It has explained the factors that led to the current man being unique and special. The lack of explanation of the major diversities among people around the world, who the book claim came from same ancestral origin, is wanting. However, the book has good and interesting viewpoints that are worth the read.
Lewis R., (2010). Human Genetics: Concepts and Applications. (9th Ed.). Berkshire, England: McGraw-Hill.