Mtdna Sequence Of Modern Europeans example essay topic

The origin of mankind is a question that has challenged historians for centuries. Although most recent histories are carefully documented, the bulk of the story of humanity, prehistory, remains largely unknown. In his book The Seven Daughters of Eve, Professor Bryan Sykes attempts to explore the mysterious field of human evolution and connect the modern population to their distant ancestors. The artifact he uses to bridge the present to the past is mitochondrial DNA, "the traveler from an antique land who lives within us all". (Sykes, 2001, p. 1). Being a short strand of genetic material in the mitochondria, this DNA (mtDNA) has far fewer nucleotide bases and a higher rate of mutation compared with the chromosomes in the nucleus.

The fact that mtDNA is inherited maternally without recombination makes it valuable to anthropology as it preserves information about ancestry. Through his research experience with mtDNA in the study of the Iceman, the prehistoric Europeans and various other subjects, Sykes reaches the conclusion that all modern Europeans descended from seven women, "the seven daughters of Eve". Through careful experiments and scientific research, mtDNA is able to provide a convincing outline of human evolution in the last million years. However, it is by no means the perfect solution. The general theory Sykes constructed, that modern humans were derived from one or a few ancient females that diverged and spread to the continents, is consistent with a number of pieces of archeological and biological evidence.

However, when the details are examined, the claim that all modern Europeans descend from seven individuals is not completely credible. In addition, the presence of ambiguous clusters of gene networks seems to defy the argument that mitochondrial DNA is inherited exclusively from females. Two distinct models have been proposed to explain the origin of modern man. The "Multi regional Hypothesis" states that all modern Homo sapiens developed in parallel from separate populations of Homo erectus in Africa, Europe and Asia.

In contrast, the "Out of Africa Hypothesis" states that the modern Homo sapiens evolved from a single source in Africa and spread to Eurasia through colonization. In The Seven Daughters of Eve, Sykes concludes that the evidence extracted from mitochondrial DNA supports the "Out of Africa Hypothesis" and argues that all modern men were derived from "only one ancestor, the mother of all Africa and the rest of the world". (Sykes, 2001, p. 276). One particular group of descendants from this "mitochondrial Eve" (Sykes, 2001, p. 276), the clan of "Lara" (Sykes, 2001, p. 278), migrated from Africa 100,000 years ago and eventually occupied all of Eurasia. The claim is further confirmed through genetic research and archaeological evidence. According to scientists, African populations have the most ancient alleles and the greatest genetic diversity, indicating that they might be the oldest human population in existence.

In Europe, where the evidence for a localized origin of humans seems the strongest, archaeological artifacts, including advanced weapons, sophisticated tools and artworks - signs of a highly developed culture and an indication of the presence of the Cro-Magnon - have been found in geographical progression. This important clue suggests that the Cro-Magnons (ancestors of modern Europeans) did not rise independently from different origins but instead derived from one source and radiated from one geographical location gradually through migration. The colonization of modern man coincided with another important development. Just around the time when the first humans were thought to have appeared in Asia, Australia, New Guinea and the Americas, a huge variety of local animal species mysteriously disappeared. The near-simultaneous extinctions of so many large species indicate that the modern man must have migrated to these areas very recently in prehistory, instead of evolving from local protohuman populations. According to the current theory, most big mammals survived in Eurasia and flourished in Africa because they coevolve d with humans for millions of years and had ample time to learn to survive the humans.

The animals in Australia and America, however, had the misfortune to be suddenly confronted by modern humans armed with superior hunting techniques and therefore became extinct. Bryan Sykes' mitochondrial research supports the "Out of Africa Hypothesis" and is consistent with archaeological records. A parallel conclusion is reached proposing that all modern Europeans originated from seven women who lived between the last 20,000 and 15,000 years ago. Unlike the previous conjecture, this hypothesis is more detailed and problematic. Around the time when these women are supposed to have lived, modern humans had already taken a firm root in Europe and their population would certainly have exceeded the thousands. Sykes acknowledges this fact when he comments: "A clan mother did not have to be the only woman around at the time and she certainly wouldn't have been".

(Sykes, 2001, p. 199). Then why did the offspring of these seven women alone thrived while the vast majority of others became perished or lost? Sykes suggests that "at some point between then and now [other women's] descendants in the female line either had no children or produced only sons". (Sykes, 2001, p. 199), but this statement alone is not sufficient to account for the massive genetic drift, of which out of tens of thousands of women only seven individuals passed their mtDNA to future generations. A possible explanation for this curious phenomenon is that the rate of mtDNA mutation is slower, and the seven clan mothers actually lived before the occupation of Europe by the Cro-Magnons. Then, through successive waves of colonization, the descendants of the seven women migrated through East Asia into Europe.

Their mtDNA, through the founder's effect, became dominant in Europe and got passed on to the modern Europeans. In fact, investigations done by several other scientists have yielded different rates of mtDNA mutation. A 1999 report claims that mtDNA mutation rates differ in some groups of animals, and the divergent dates for some animals calculated from mtDNA do not match the fossil records. The conclusion that all modern Europeans derived from seven women living so recently is not very convincing. Another puzzling aspect of Sykes's tudy of mtDNA is the occurrence of ambiguous clusters of gene networks. In Chapter 10, Bryan Sykes mentions that during his research conducted on the mtDNA sequence of modern Europeans, he encountered several cases in which related genetic sequences cannot be constructed in an evolution tree.

In his example, two separated sequences, sequence B with a mutation at position 311 and sequence C with a mutation at position 189 arise from the reference sequence. Then, a sequence with mutations on both position 189 and 311 emerge and claims to be descended from both sequences B and C. To solve this problem, Sykes arranged the sequences in a network instead of a tree (see page 140), and decided that sequence D was derived from both sequence B and C. This organization seems to contradict the claim that mtDNA can be inherited from the females alone. If sequence D had indeed developed from sequence B and C, then two strands of mtDNA, instead of one, contributed to forming the mtDNA D for the next generation. If one of the mutations came from the mother, then the other one must have came from the father. In another study published 1999, scientists suggest the rare possibility of mtDNA recombination through another clue. If the mtDNA is only inherited from the mothers, then the correlation between different mutations should not depend on how far on the genome they are, because each of the bases on the control region of the mtDNA has the same chance of having a point mutation.

Instead, their measurements show that mutations at distant sites along the genome are less likely correlated than those on nearby sites. Possibly, the occasional inputs of mutations from the fathers, who are likely to have mtDNA sequences similar to that of the mothers, increased the chance that nearby mutations on the mtDNA are related. Although the mechanism for mtDNA recombination is still unknown and disputed, mtDNA recombination between the male and the female is a remote possibility. Aside from minor ambiguities, such as the disagreement at the rate of mtDNA mutation and the likelihood of mtDNA recombination, the theory that all modern humans are derived from a single female, confirming the "Out of Africa Hypothesis", is well supported with archaeological and biological evidence.

Modern science cannot construct a complete account of prehistory packed with accurate details, but The Seven Daughters of Eve outlines the major biological stages in human evolution, and Sykes' imagination supplies the living continuity of the story in the gaps of fragmentary evidence. The real lives of the clan mothers can never be told, but their hypothetical experiences are highly representative and typical of prehistoric humans. The significance of this root-searching cannot be ignored. It prides a reader to learn how his / her distant ancestors had struggled against the harsh realities of prehistoric life to bring humanity to dominate the world. A sense of honor and unity is aroused when one traces his / her roots back to the ancient clan mother, and realizes his / her blood is bonded to the 6 billions souls living around him / her. Yet, the importance of this root also cannot be exaggerated.

After all, the universal origin of man is only a distant past, and one must observe the present and look forward to the future. Although all of us as a biological species can trace our ancestry to the same woman, we have nonetheless isolated ourselves into different factions, cultures, nationalities and ethic groups. The question we face right now is not so much how we can relate ourselves through our clan mothers, but which of the many descendants of these clan mothers can out-compete and survive the others. The Chinese and the Japanese may care less if they know the obvious fact that both have derived from the woman No; the ruthless political and economic conflict of the two groups has obliterated their respect for a common ancestry. Of all the things the story of human evolution has taught us, the lesson of the Neanderthals stands out above the rest: the reminder that extinction is a real threat, and that any faction that lags behind will be eradicated and replaced by another.

If we do not remember the fact that nature is a brutal struggle, and that human evolution too is based on the cruel principle of competition and natural selection, we will become extinct. One day, much as Sykes had pondered over the Neanderthals, some alien race will hold our skulls and wonder why we have vanished.