Q.1
Neanderthals are European hominins. On the other hand, the Denisovans are Asian hominins. They are named after the Denisovan Cave located in Altai Region, Siberia. Based on mtDNA sequence analysis, the Denisovans were identified as a discrete group. Molecular data shows that the Denisovans and the Neanderthals split between 381 kya and 473 kya.
Q.2
According to the “Last Human Standing” documentary bout 50, 000 years ago, three varying kinds of humans lived together. In this film the researchers explore why modern humans survived while their ancestral cousins became extinct.
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Q. 3
The documentary relied on mtDNA to trace the evolution trajectory of modern humans. Using mtDNA limits the paleogenetic research because the mtDNA only cover the matrilineal ancestry. Since the “Last Human Standing” documentary aired, a lot has changed. Paleogenetic research no longer relies on the mtDNA but aDNA which takes into account both the matrilineal and patrilineal ancestry.
Q. 4
Sequencing the aDNA gives insights into the Neanderthals and Denisovans. Hybridization between the hominin groups and modern humans indicate that the Neanderthals were more connected to Asians and Europeans than Africans. Modern human genomes comprise of about 30% of the Neanderthal genome. Approximately 1 percent to 2 percent genome of individuals from outside Africa is derived from the Neanderthals. The hybridization between the Denisovans and modern humans is evident in oceanic populations. About 5 percent to 6 percent of the oceanic populations’ genome is derived from the Denisovans.
Q. 5
Ancient DNA, aDNA teaches about the demographic structure of the Neanderthals and Denisovans by making inferences about their population history and size. According to the Neanderthals genomic data, their population significantly decreased towards their extinction. Three evidence line support the small population of the Neanderthals before they became extinct. The coalescent method is the first evidence supporting the small population of the Neanderthals. It allows the use of genetic sequences to define the possible population genetic parameters that could be identified in the past. Next is the many deleterious genomic variants of the Neanderthals. Relative to the modern humans, the Neanderthals had higher amounts of non-synonymous mutations compared to their synonymous mutations. This aspect indicates that the Neanderthals had small population because were the population larger, natural selection would gave weeded out the deleterious variants. Finally, is the low heterozygosity levels among the Neanderthals. Besides, the aDNA derived from the Neanderthals shows that they had consanguineous relations. A Neanderthal female was identified to be an offspring borne of the relations between an uncle/aunt, halfsiblings, grandfather/grandmother, niece/nephew, or grandson/granddaughter. The inbreeding was identified through the homozygosity stretches in their genomes; the stretches were longer than expected. However, while the aDNA from Denisovans also illustrated low heterozygosity levels, it did not indicate inbreeding because none of the sequenced aDNA from the Denisovans had long homozygosity stretches.
Q 6.
This research gives important insights on the evolutionary trajectory of modern humans. It provides a clear understanding of the changes that occurred after modern humans split form their last shared common ancestor with the Denisovans and Neanderthals. The aDNA highlights the interactions between contemporary humans that migrated out of Africa and the hominins whose evolution took place in Asia and Europe. Hybridization between the hominins and the contemporary humans migrating out of Africa provided the latter with the advantageous increased genetic variation. The Denisovans and Neanderthals had lived for hundreds of thousands of years adapting the Asian and European environment since they had genetic variants appropriate for living in those regions. Some of the genes transferred through hybridization were associated with adaptive new diets and attitudes, skin color, immunity, and hair traits. Therefore, modern humans evolved through their hybridization with the Neanderthals and Denisovans.
