Y chromosomal Adam

Y-chromosomal Adam is the name given to the patrilineal most recent common ancestor (MRCA) of modern humans. In other words, he was the man from whom all living humans today descend, on their father’s side, and through the fathers of those fathers and so on, back until all lines converge on one person. He is the male counterpart of Mitochondrial Eve, who,lived in north-western Botwsana around 177,000 years ago (confidence interval ± 11,300 years).

When I did my first Y-DNA test in 2012 with the National Geographic’s  National Genographic Project, it gave a date of 60,000 years ago (60 kya) for Y-chromosomal Adam. This was already outdated, as other recent estimates around that time gave dates ranging from 120 to 160 kya. By definition, it is not necessary and highly unlikely that Y-chromosomal Adam and Mitochondrial Eve lived at the same time or in the same location.

However, in 2013 scientists announced the discovery of an extremely ancient Y DNA haplogroup from a sample submitted for an African-American man in the USA.  Y-chromosomal haplogroups are defined by mutations in the non-recombing portions of DNA from the Y chromosome. These mutations accumulate at the rate of roughly two per generation. The accumulation of mutations in the descendants of Y-chromosomal Adam allow us to map out the major branches of the family tree in terms of Y-haplogroups. This discovery adds a completely new branch to the Y-DNA family tree and pushes back the age of Y-chromosomal Adam to around 250 to 300 kya.

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Becoming Human Part 2

This is the second part of a post summarizing current understanding of the evolution of humans. In the previous post, I outlined the evolution of pre-human species from the first monkeys around 35 million years ago (Mya) to the appearance of the first human species around 2 Mya. This post takes a look across the evolution of humans from the appearance of the first human species Homo habilis to the appearance of anatomically modern Homo sapiens sapiens around 250 thousand years ago. The following figure summarizes the evolution of humans over the last 2 million years, based on [1] with some modifications to take account of some recent discoveries.

The evolution of humans (the genus Homo) over the last 2 million years. Updated from Figure in Wikimedia. User:Conquistador, User:Dbachmann / CC BY-SA. (https://creativecommons.org/licenses/by-sa/4.0)- . The late survival of robust australopithecines (Paranthropus) alongside humans until about 1.2 Mya is indicated in purple. The rapid “Out of Africa” expansion of H. sapiens is indicated at the top of the diagram, with admixture indicated with Neanderthals, Denisovans, and unspecified archaic African hominins.

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Becoming Human Part 1

Our understanding of the evolution of us modern humans has changed dramatically in the last few years as ancient genomes are decoded and we discover that humans, Neanderthals and Denisovans interbred, and also in the remote past interbred with previously unknown “superarchaic” human groups.  Scientists are also discovering new species of extinct hominids, and no doubt will continue to shed further light on our origins. Just to try to sort out the big picture in my own mind and to put these various discoveries in context, I’ve tried to summarize what we think we know, or at least what the evidence available to date suggests. This will no doubt continue to change.

This is the first of two posts and summarizes the evolution of pre-human species from the first monkeys around 35 million years ago (Mya) to the appearance of the first human species around 2 Mya. A following post will summarize the evolution of humans from the appearance of the first human species Homo habilis 2 Mya to the appearance of anatomically modern Homo sapiens sapiens around 250 thousand years ago and  mitochondrial Eve, who lived around 178,000 years ago.

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My maternal ancestors – from Eve via ice age Europe to Victorian England

In an early post on this blog, I summarized my maternal-line ancestors and where and when they lived. In the last 6 years, there have been substantial revisions to estimates of the dates associated with these mitochondrial DNA (mtDNA) haplogroup founders, and revisions to the mtDNA haplogroup tree (deep-maternal-ancestry-and-mtdna) and this post provides an update. I am a member of mtDNA haplogroup U5, which is one of nine native European haplogroups stemming from haplogroup U which most likely arose in the Near East, and spread into Europe in a very early expansion. The presence of haplogroup U5 in Europe pre-dates the last ice age and the expansion of agriculture in Europe. Today, about 11% of modern Europeans are the direct maternal descendants of the founder U5 woman. They are particularly well represented in western Britain and Scandinavia. My more recent maternal ancestors were part of the population that tracked the retreat of ice sheets from Europe at the end of the last ice age and re-colonized Britain about 12,000 years ago.

The mtDNA sequence at the root of each haplogroup arose from one or more mutations in the mtDNA of just one woman, and the age of the associated haplogroup gives the time in the past when this specific woman lived. To emphasise that the maternal clan founders were real individuals, I have used the names given to them by Sykes [1] and Oppenheimer [2] and given my own names to the more recent subgroup founders. The Table below summarizes these founders, dates and locations and is followed by brief biographies. The haplogroups are identified by the labels used in Build 17 of the ISOGG mtDNA tree which can be accessed at http://phylotree.org/ [3]. Dates in the table below have been updated using most recent available dating estimates as described in my previous post deep-maternal-ancestry-and-mtdna.

The migration path out of Africa into Europe of the “grandmothers” linking mitochondrial Eve through to Ursula (U5) is shown on a map in my previous post deep-maternal-ancestry-and-mtdna. The subsequent migration from Europe to Britain is shown in the map below.

Figure 1. Migration path of my maternal ancestors from Ursula (U5) to Viviane (410 CE). A map of the earlier migration from mitochondrial Eve to U5 is included in an earlier post.

Updated biographies of my maternal haplogroup great* grandmothers follow below.

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Our Asgardian ancestors

I grew up reading northern European myths and legends, including tales of Odin, Thor, and the other gods of Asgard. I was largely unaware of the Marvel comics appropriation of Thor and other Asgardians as superheros until the Marvel cinematic universe started to hit the big screens in the last 12 years.

Loki, Thor and Odin (from the Marvel Cinematic Universe)

I have only recently come across the growing evidence that an Asgardian was one of our ancestors, way back near the beginning of the evolution of life, when the first eukaryotic cell appeared. Eukaryotes are organisms whose cells contain membrane-wrapped internal structures, such as a nucleus, unlike prokaryotes (Bacteria and Archaea), which have no membrane-bound internal structures.

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Deep maternal ancestry and mtDNA

In February 2014, I did a series of posts on my deep maternal ancestors, identified through a test of mutations on my mitochondrial DNA (mtDNA) which is inherited only from the mother. This test was carried out by Ancestry.com, who have since discontinued tests of mtDNA and Y-chromosome DNA. Costs of DNA tests have dropped dramatically since then, and late last year I ordered an mtDNA test from FamilyTreeDNA (www.familytreedna.com) which carried out a full sequencing of the mitochondrial DNA.

As well as the DNA that makes up the chromosomes in the nuclei of our cells, we also have another type of DNA called mitochondrial DNA (mtDNA). The mitochondria are organs located outside the cell nucleus which convert sugars into energy.  Mitochondria have a small circular loop of DNA, containing only approximately 16,569 base pairs in humans. The circular mtDNA is similar to the DNA of bacteria, and it is thought that mitochondia evolved from symbiotic bacteria that were once free living.

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Other worlds

As a teenager I was fascinated by astronomy and cosmology and read voraciously as well as spending many hours outside at night with my telescope and Norton’s Star Atlas. During my brief years as a physicist in the 1970s, I kept up with the literature and was aware that some astronomers were attempting to detect planets around other stars by detecting the gravitational jiggling of the star around which the planet was orbiting. But these movements were slightly beyond detection by the technology of the day.

Headlines with messages like “First Planet Found Outside Our Solar System” appeared in newspapers dozens of times, at least twice in the New York Times, and once on the front page. But all these announcements were subsequently found to be wrong. And in one notorious incident, it was later found that the astronomer had detected not movements in stars, but movements in the telescope itself. So I was stunned to discover on reading the book “The Stardust Revolution” that new detection methods combined with space-based telescopes had resulted in the proven discovery of nearly 2000 exoplanets.

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