The Denisovans--An ancient type of human

by Darvin Martin on Thursday, August 30, 2012 at 10:25pm ·

The Denisovans

The genome of another ancient type of human has been decoded. The Denisovans lived in Eastern Asia up to about 30,000 years ago, parallel to the Neanderthals in Europe. When comparing the Denisovan genome to genomes of living humans around the world, humans in Southeast Asia share about a 6% greater similarity among these differences than the rest of the population. When comparing the Neanderthal genome to genomes of living humans around the world, we find that Europeans share between 1-4% greater similarity (among the differences between Neanderthals and modern humans) than the rest of the world population.

All humans around the world living today descend from common ancestors living in East Africa between 140,000 and 200,000 years ago. The Denisovans and Neanderthal represent far more ancient human lines that moved out of Africa to settle in Europe and Asia between 350,000 and 600,000 years ago. About 60,000 years ago, modern humans of the yDNA haplogroups C and D moved out of Africa at the southern end of the Red Sea between Djibouti and Yemen. The followed the coastline of the Indian Ocean. Both found their way to India. From there the C groups settled in Southeast Asia, arriving in Australia at least 40,000 years ago. The D groups transverse China and settled north as far as Korea and Japan.

In Southeast Asia, some modern humans within the C groups interbred with the ancient human Denisovans living there. This occurred often enough for markers of Denisovan DNA to be found in the modern human population. Madame X, our Denisovan DNA source, lived in the Altai Mountains of Siberia 41,000 years ago. Modern humans probably drove the Denisovan populations to extinction, and perhaps the populations in South East Asia were already facing extinction when Madame X lived in Siberia. It is unknown if or how Denisovans relate to the Homo floresiensis population in Indonesia, since DNA has not been successfully extracted from Homo floresiensis remains.

Our first modern human ancestors to enter Europe also interbred with Neanderthals, as evidenced by Neanderthal markers found in the modern European population today. These were probably the Cro-Magnon with yDNA haplogroup I and a minority of K and G also represented.

Denisovan DNA adds to the complexity of early human origins. While the direct paternal (yDNA) and direct maternal (mitochondrial) DNA of all living humans have the same “recent” source in East Africa, our autosomal DNA, representing the mixing between both parents, shows a far earlier genetic history, connecting to earlier groups of humans that have long since gone extinct.

Denisovan Molar, Credit: the Max Planck Institute of Evolutionary Anthropology

Modern human yDNA world family tree

 

Darvin L. Martin

Brownstown, PA

717-201-4050

If we have African Ancestors, how did we become white?

If we have African Ancestors, how did we become white?

by Darvin Martin on Thursday, June 14, 2012 at 8:03pm ·

That’s an excellent question! Typically, one person dares to ask such a question when I give a seminar or presentation about DNA and human origins. Many others think about it, but do not ask. The type of DNA work I'm involved with really helps us get a hold of the dynamics which play a huge role in forming the differentiating characteristics between people groups. And the differences are very small indeed.

Prior to and during the out-of-Africa migration of modern humans, ~60,000 years ago, all our human ancestors leaving Africa were very dark skinned. We see evidence of this among the people of Sri Lanka, South India, the Andaman Islands and indigenous peoples from New Guinea and Australia. Evidence suggests, through DNA and archeology, that this migration followed the southern coast of Aisa.

In every case, as people moved further north, skin color began to lighten. This change that is expressed in lighter skin color and hair color has multiple genetic components. It’s a complex assortment of mutations, and in fact different sets of changes can produce the same lighter skin color results independently of each other. And none are strictly related to the y-chromosome, although yDNA haplogroup designations and migration patterns can be used to understand the migratory patterns of ethnic groups in relation to such changes.

The gene MC1R located on chromosome 16 plays a huge factor is melanin production. Those of British and Irish descent with red hair and very fair skin have a mutated variant of this gene. In north Asian populations the variant of MC1R is different than in Europe, still contributing to lighter skin color, but not to red or blonde hair.

Another gene impacting skin color for Europeans is SLC24A5 found on chromosome 15. 98.7% of Europeans have an SNP change from A to T at location rs1426654, the 111th amino acid sequenced within the gene SLC24A5. 93% of Africans have an A at this location. A is the original value. However Asians, even those of lighter skin, have the African version of SLC24A5.
Lighter skin allows for better absorption of UV rays that aid in the production of vitamin D, essential for human health. Darker skin reflects UV rays, helping to protect us from melanoma. In climates where the sun is intense, dark skin is selectively preferred. People with light skin living in sunny climates have increased chances of melanoma. As communities migrated north, living in colder climates and in the mountains, they wore more clothes, thereby producing a selective advantage for children born with lighter skin. These children could absorb more UV rays through the smaller portion of skin that was exposed to the sun. These changes occurred subtly and were not readily noticeable within a population group at any given. The changes were noticeable as one group compared itself to another.

Lighter colored skin certainly occurred in north India among our R haplogroup ancestors. In fact, one can clearly see the color continuity today from pale skin in the Hindu Cush and Himalayan Mountains to the very dark skinned peoples of southern India. These changes in skin color in northern India probably started to become noticeable 30,000 years ago – about 1,000 generations ago. The same would have occurred in the Caucasus among the G haplogroup around the same time period, and to some extent even earlier among the Cro-Magnon peoples of Ice Age Europe, who I suspect were part of haplogroups G, I, and K. Cro-Magnons were darker than modern Europeans, but also lighter than their African ancestors.

Since so many Europeans have the bulk of their ancestry within haplogroup R, I need to conclude that perhaps the change of skin color in north India had the largest influence on current Europeans. Last week I had lunch in Baltimore with a Sikh from Punjab (in northern India). His skin color is identical to my own. We had some time, so I rehearsed some of my DNA findings with him, and we discussed the likelihood of a shared ancestry up until the point that my ancestors moved west from north India around 20,000 years ago. He resonated well with this, but was less receptive to the idea that all ancestry, even Indian, eventually leads back to East Africa. In a scientific quest to understand human origins, DNA appears to challenge presuppositions across the globe.

Darvin L. Martin
Brownstown, PA
717-201-4050
dlmartin@genealogygoldmine.com