Tag Archive: Genographics

Neanderthal and Densovan

DNA Molecule

A schematic of a DNA molecule. (Public Domain image from Wikimedia commons.)

Homo has been spreading out of Africa since long before the evolution of “true” or “modern” humans.  But what exactly is a “true” human? What is a species?

Once it was simple. God made the species, which were unchangeable. Then the naturalists got into it, and the head-scratching began. The recognition that species could actually go extinct made more problems yet. Which modern species were they most like? Were they even “new” species, or variants of modern ones? Remember that the first “natural histories” included some very odd beasts from travelers’ tales, some of which were probably at fourth and fifth hand.

Comparisons within the human family tree have always been particularly fraught. Quite aside from the fact that many still refuse to accept the evolution of human beings, every paleontologist wants to be remembered as the discoverer of a new species. But it seems likely that Homo habilus, Homo erectus (who left Africa and included the subspecies Neanderthal and Denisova) and Homo Sapiens were valid species in that it is unlikely that an early Homo Habilis could have interbred with a late Homo erectus – though DNA is providing some surprises.

Even a relatively few years ago, when Jean Auel’s first book was published, the idea that Homo Sapiens, the upright and noble cave artists, could have interbred with brutish Neanderthals was laughed at by many anthropologists. Physically impossible! Any such rare hybrids would have been sterile, like mules!

Then DNA sequencing from bone fragments became possible. DNA of two variants of Homo Erectus, Neanderthal and Denisovian, was successfully sequenced. Bits of Neanderthal and Denisovan DNA were found in every human population except those of pure sub-Saharan African descent.

Love or war? We don’t know and most likely never will, but probably both. Obviously our DNA was still compatible. It is quite possible that the “extinction” of the Neanderthals by Homo Sapiens was more of a genetic swamping. We even know what some of the Neanderthal genes we retained were – part of our modern immune system. Makes good sense: the Africans would be wide open to cold-adapted parasites and diseases, while the Neanderthals had adapted to them over a couple of hundred thousand years.

We know far less about the Denisovans, though since I turned out to have a whopping 3% Denisovan, I’m going to be following their story with considerable interest.

DNA Molecule

A schematic of a DNA molecule. (Public Domain image from Wikimedia commons.)

I started with the family tree my mother wrote out in my baby book, added research from relatives on both sides of my family, and generally have a pretty good idea of where my ancestors came from. I’ve traced all branches back to before the Civil War, and in some cases to before the Revolutionary War. My baby book lists English, Irish, Scotch, Dutch and French origins, though quite a few generations back. I allegedly have some French-Canadian trapper ancestry though my maternal grandmother, and on that basis and physical appearance we sometimes think the family has a little Native American background. So I was interested in what Genographics would make of me.

Genographics give the percent of your total ancestry matching native groups from 9 different regions. The regios are:
Northeast Asia
South African
Southwest Asian
Native American
Southeast Asia
Northern European
Sub-Saharan Africa

Well, mine showed no Native American. My DNA results for the whole genome are fairly typical European: 45% Northern European, 37% Mediterranean and 16% Southwest Asian. That doesn’t rule out the possibility of a very tiny contribution from Native Americans, but it certainly doesn’t confirm it.

This doesn’t mean my recent ancestors came from these parts of the world! My profile is very similar to that of people who’ve lived for several generations in England, and even closer to those from Germany. The mixing probably took place several thousand years ago.

The Northern European component probably represents the original hunter-gatherer population of Northern Europe. These people may be descended from the Cro-Magnons. Genographics doesn’t say anything about skin or eye color, but I suspect blue eyes and light hair evolved in this component simply because they lived for a long time in a relatively low-sunlight environment where these traits would have had little cost and considerable benefit in production of vitamin D.

The Mediterranean component probably represents the partial replacement (with considerable interbreeding) of the hunter-gatherers by Neolithic farmers moving north and west from the early farming communities of the middle east. This movement is thought to have started around eight thousand years ago.

The Southwest Asian component probably had a similar origin, perhaps coming from father east in the fertile crescent, the origin of western Eurasian agriculture.

So no surprises, just a rather bland typical European background. What I found most interesting was the Neanderthal and Denisovian fractions of my genome – but more of that later.

DNA: We All Have It

Where did we come from?

A schematic of a DNA molecule. (Public Domain image from Wikimedia commons.)

A schematic of a DNA molecule. (Public Domain image from Wikimedia commons.)

I just got the results from my Genographic DNA study, and I thought I’d share them. To start with, I thought I’d explain a little about DNA, and how the Genographics study uses it.

DNA is the abbreviation for deoxyribonucleic acid, and thank goodness it has a widely used abbreviation! If you enlarged a molecule of it enormously it would look rather like a twisted ladder with four different kinds of “rungs.” The genetic information is coded by the order of these kinds of rungs. I’m not going to get technical here, but if you want more information have a look at Wikipedia.

DNA is the information-carrying part of chromosomes. Most normal human beings have 46 chromosomes: 23 from the mother and 23 from the father. (The rare exceptions generally have some kind of medical problem, such as Down’s Syndrome which results from having three copies of one particular chromosome.) These chromosomes are in the nucleus of just about every cell in your body. In addition, the cell body has structures called mitochondria which are essential for metabolizing nutrients. These mitochondria have their own DNA, but since the cell body and mitochondria come from the egg cell, the mitochondrial DNA is inherited only from the mother.

There is one pair of the 23 which is special, called the sex chromosomes. These chromosomes come in two forms, X and Y. The Y-chromosome determines maleness, and seems to have little other genetic information. The X chromosome has a normal complement of genes. A normal woman has two X chromosomes. A normal man has one X (from his mother) and one Y (from his father.) Individuals with other combinations such as XXY occur rarely. The important thing for us is that Y chromosomes are passed only from male to male.

Thus there are three types of genetic analysis which can be done: nuclear, mitochondrial and Y-chromosome.

The nuclear DNA is what makes me, me and you, you. It comes from both parents, and is remixed in every generation. Your nuclear DNA can be compared with that of indigenous populations throughout the world, and interpreted as what percent of your ancestry came from what area.

Mitochondrial DNA is passed almost without change from mother to child. Thus my mitochondrial DNA is the same as my mother’s mother’s mother’s mother’s mother, a woman named Ellen Carr. Changes do occur, very slowly, and these can be used to track back how my maternal line traveled out of Africa.

I don’t have a Y-chromosome, so the Genographics results don’t give me any information on my father’s line. A cousin, a son of my father’s brother, has been tested by another company, so I know I am in Bowling Group 6. But I don’t have the pathway my paternal ancestors took out of Africa.

Next week I’ll retell the story Genographics told of my maternal line.