Why biological monogenism for humans is almost certain

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Neanderthal penguin

Neanderthal penguin

A question often asked by Catholics is this:

“Was there a single original human couple from whom all future men are descended, or can the origin of the human race only be traced to an original group of more than two people? These alternatives have been given the names ‘monogenism‘ and ‘polygenism,’ respectively.”
– Kenneth W. Kemp, “Science, Theology, and Monogenesis

Note: this post assumes evolution of hominids from a previous common ancestor.

It is generally considered Catholic teaching that monogenism is true. For this, see “Adam & Eve of Genesis: Historical & the Primal Human Pair?” by Dave Armstrong … and “Did Neanderthals have a soul?” by Dr Robert Kurland at his “Reflections of a Catholic Scientist” blog.

In the former, however, Dr Kurland says this:

“It is unlikely, but not impossible, that biological monogenesis occurred.”

I think that biological monogenism is not hard to maintain, and I think it’s actually hard to avoid. I’ll explain why … as background you’ll need to look up the concepts of most recent common ancestor (MRCA), and identical ancestors point (IAP), and pedigree collapse – Wikipedia explains them nicely, and I’ll try to do so here briefly.

The time spans I’ll mention are so short that I need to clarify that I am not coming from a creationist perspective, and believe in human evolution over hundreds of thousands of years, or longer.

Let’s start with me. I have two parents. Four grandparents. 8 great grandparents. 16 great great grandparents. And so on. Going back 20 generations, I have just over 1 million ancestors. 30 generations – 1 billion ancestors. 34 generations and I have more ancestors than hominids that have ever existed. But 34 generations is definitely AD, not BC. So something is wrong there. 1000 years ago there were definitely not several billion humans on the planet. And the explanation is pedigree collapse. I have 4 grandparents. A friend of mine only has 3, because a pair of first cousins once removed got married to each other. I have third cousins I cannot identify as such, and could easily marry one without knowing it. Think of that on a massive scale – it’s not just royal families that do this. It’s the very reason a large population can descend from a smaller population without having more ancestors than that smaller population allows for.

Le Moustier - Neanderthals

Le Moustier – Neanderthals

Our most recent common ancestor – we have one. We must, unless we evolved from different amoebas, and the early hominids we evolved from were divided into completely separate unrelated groups derived from multiple different amoebas. Monogenism, the type we’re talking about, requires the most recent common ancestor (MRCA) of all humans to be human … otherwise we have polygenism, with two or more separate non-human groups resulting in two separate evolutionary events that resulted in humans. For modern humans to have separate evolutionary origins (for races, or geographical areas, for instance) a HUGE feat of separation must have occurred preventing interbreeding, which would have eventually resulted in a common pedigree, and common ancestors WITHIN humanity.

Recently some clever population dynamics people did some clever maths – see the two articles by Douglas L T Rohde in the references below. Assume a situation where we have a) our current population size, and b) a situation where, throughout history, geographical boundaries and race and language and monogamy are taken out of the equation, and human mating is random. I.e. for each child born, their parents mated randomly, regardless of partners producing prior offspring, regardless of distance between them, etc. Not physically possible, but for the purposes of the maths, that’s what they did. And their result? Under such circumstances, we are all descended from one individual who lived … in the 1200s AD … 800 years ago.

Once you include the variables of distance and language and marriage, etc., we end up with a REAL, probably date for the most recent common ancestor of all humans alive today. And that date is between 1800 years ago and 5000 years ago.

And that means our most recent common ancestor is not Adam or Eve, but one of their descendants.

If you read up on the MRCA, you’ll know that there is something about this that is a very tricky thing to understand. At the time that our MRCA lived, there were not just two people. There could have been hundreds, thousands, millions. Bottlenecks exist and influence this, but they are not required for this to work out the way it does. Some people alive then bred, some did not. Of those who bred, not all their descendants bred. So while there may have been 1728296 people alive at the time our MRCA lived, some have no descendants alive today, some are ancestors of some people alive today, some are ancestors of most people alive today, but only the MRCA is the ancestor of every single human alive today. And if that ancestor was monogamous, then it’s really a couple who are our MRCA.

Every time someone dies, the exact identity of that MRCA might change. The MRCA today is not the same person (or couple) as the MRCA of 10 years ago, or 100 years ago.

The identical ancestors point (IAP) – a bit more tricky. Our MRCA had ancestors, and they are, by definition, ancestors of everyone alive today, but they are not our most recent common ancestors. And the population our MRCA was part of – they had their own most recent common ancestor. And if you go back in time, you’ll reach a point where every single person alive at that time fits into one of two groups – those who have zero descendants today, and those who are ancestors to everyone today. (This took me weeks to come to understand properly!)

And when is our probable IAP? Depending on who does the calculations, and how they incorporate groups with significant isolation in their history (e.g. various aboriginal peoples) – 15000 years ago to 100000 years ago.

Mitochondrial Eve and Y-chromosome Adam? Their identities also change as time passes, and people die, and the genetic make-up of the population varies. Imagine everyone in the world except all my maternal grandmother’s descendants die from a nuclear holocaust. Suddenly my maternal grandmother is Mitochondrial Eve, and she and my grandfather are our MRCA couple, and all we can say about Y-chromosome Adam is that he probably lived in England in the last few hundred years.

Human chromosomes

Human chromosomes

Remember that our MRCA is an entire organism, or, if monogamous, an entire pair of organisms. Mitochondrial Eve is only the common ancestor for all mitochondria found in living humans today. Y-chromosome Adam is only the common ancestor of all Y-chromosomes found in living humans today. Our genes for eye colour – the common ancestor would be Eye Colour Eddie, someone else. The gene that produces the protein that would synthesis vitamin C if it worked – all humans today have that gene descended from Vitamin C Victor. Mitochondrial Eve and Y-Chromosome Adam are just the common ancestors for those genes that have been made popular by naming the people they came from.

So … where does this get us today?

Our most recent common ancestor probably lived within the last 5000 years. Our identical ancestor point – within the last 100000 years. And the IAP is very useful in deciding monogenism. Were all the people we are descended from at that time human? Or were there two species of hominid, e.g. Neanderthals, that were part of that group? (Remember that even if only Homo sapiens sapiens was part of that group of our ancestors at the IAP, their ancestors could have mated with Neanderthals prior to that, and thus allow Neanderthal genetic material into the eventual human population, either all or only part of the population.)

And very, very important in determining who “humans” were – remember that the way we speciate hominids results in separate groupings that are not necessarily what God considered to be separate groups. Our methods of species classification are simply our own. There is still debate as to whether Neanderthals are a separate species, or a subspecies of Homo sapiens. Even in recent times, some have tried to classify human races as being of separate species origin. We know better now, but we are still flawed, and we are basing our classification on who lived where and how they differed, and not on God’s original decision, “Let this group be called Man, and let this part of the group have ancestors in 2015 AD, and let these two people be the MRCA of all alive in 2015 AD.”

From a theological perspective, I imagine what God called Man came into being the moment before he revealed himself to the group he decided was Man, and from that moment, man sought to have a relationship with God, and so it becomes irrelevant whether that was two individuals taken out of a population of Homo sapiens sapiens and put in the garden of Eden (and later perhaps even permitting ensoulment of those in the original population their immediate descendants took as spouses, and certainly subsequent children), or whether that was a group made up of 1421 Homo sapiens and 23 Homo neanderthalensis who married into the group, or whether it was even prior to the separation of modern humans and Neanderthals (which allows for at least two groups of what God considered Man to be capable of seeking God.)

Homo neanderthalensis at the Natural History Museum of Vienna

Homo neanderthalensis skeleton

All that can happen, and still leave us with a most recent common ancestor couple – Adam and Eve at one point, someone more recent today.

So, in summary:

  1. Our current MRCA is far more recent than commonly believed, and is definitely a modern human
  2. The calculated time when all people were either our ancestors or not falls well within the timeline for Homo sapiens
  3. This makes biological monogenism very, very likely, in fact almost certain
  4. Religiosity amongst Neanderthals probably means theological monogenism points to a time that actually predates biological monogenism, or at least coincides with it

Interesting side effects of having such a recent MRCA, especially if you look at the multiple MRCAs of sub-populations of modern humans (see “Common ancestors of all humans“, by Mark Humphrys, and all the interesting links from that):

  • All modern Jews are probably descended from Mohammed.
  • All modern Muslims are descended from King David.
  • All white people are descended from black people somewhere in their ancestry.
  • All black people are descended from white people somewhere in their ancestry.
  • Everyone is probably descended from Confucius.
  • Europeans (and those with recent European ancestry) are probably all descended from Charlemagne.

Interesting Catholic side effects – if you take this principle and apply it to the consecration of bishops by three other bishops (i.e. consider a bishop to be the “offspring” of three “parents”), it is entirely possible that all bishops living today are descended from the Apostles Jude and Thomas and Paul, but not James (or even Peter, because no, even our pope isn’t required to have Peter in his personal apostolic succession, because that’s not how popes are chosen – they’re successors of his office, and it’s quite possible that Paul, not Peter, made Linus a bishop.)

References and further reading:

Did Neanderthals have a soul? … by Robert J. Kurland
Did Neanderthals have a soul? … by Robert J. Kurland [another version of the article]
Science, Theology, and Monogenesis … by Kenneth W. Kemp, 2011, American Catholic Philosophical Quarterly, Vol. 85, No. 2 [PDF]
Adam & Eve of Genesis: Historical & the Primal Human Pair? … by Dave Armstrong
Common ancestors of all humans … by Mark Humphrys
On the Common Ancestors of All Living Humans … by Douglas L. T. Rohde, Massachusetts Institute of Technology November 11, 2003 [PDF]
Rohde DL, Olson S, Chang JT. Modelling the recent common ancestry of all living humans. Nature. 2004;431(7008):562-6.
Monogenism … Wikipedia
Most recent common ancestor … TMRCA of all living humans … Wikipedia
Identical ancestors point … Wikipedia
Pedigree collapse … Wikipedia
Mitochondrial Eve … Not the most recent ancestor shared by all humans … Wikipedia

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