Branching and the Founder Effect

I am basing all of my conclusions on a certain interpretation of genetic genealogy.    The Y chromosome is passed directly from father to son.  Sometimes, rarely, there is a random mutation that occurs that passes to the son which is carried forward through whatever male descendants that man ultimately has.  The rate at which such mutations happen is currently calculated at about one every 144 years as a statistical average, but this value is frequently revised.

This is what produces the tangled tree like branching observed in the study of Y-DNA lineages.  A branching event in a paternal lineage occurs when a unique mutation is inherited by sons who survive to have sons of their own who have sons of their own and so on. 

Every few generations a given male lineage will have a son born with a mutation unique to himself, but the odds of that mutation being passed on to be discovered in modern genetic testing depends on many social factors.

We cannot directly observe the entire human y-dna tree because we don’t have the dna of every man who ever lived or even those alive today.   For the most part, we have a self-selected sampling of the tree.   But since we have a quite large sampling size, we probably do get a statistically complete outline of the entire tree.   

Do such branching events tell us anything about the history of a particular male lineage, or are such events entirely random events that occasional happen independently of any distinct historic or cultural context?  My belief is that the further back in time a mutational event occurred, the more likely it is to represent some significant historic process.   There are probably historic reasons why most genetic branching events become statistically more likely to be detectable in modern populations.

These branches occur for probably the same reason branches on a tree occur.  Those twigs that randomly sprout in a location with access to more sunlight will receive more nutrition and grow disproportionally larger than those twigs with received less.   Each branch is competing with all the others for more sunlight.

Powerful families were more likely to have more sons who survive to have more sons.  The women of such powerful families would be more likely to have better nutrition and better birthing assistance, resulting in a higher probability of healthy children.  Powerful families would have control of more territory giving them access to more resources including larger numbers of women and mating opportunities.   These young men would also therefore tend to be the best equipped, best trained, likely the most athletic, and have well established social organizations committed to their protection.   That is, they were privileged elites.

A lower-class male might certainly have more sons than another, but there is less probability that whatever unique y-DNA mutations they inherit would become widely distributed through a large population of similarly situated men over time.  These men would be competing for resources on much more equal terms so one genetic mutation would have no higher probability generation by generation of becoming more numerically dominate than would that of some other nearby lineage.   A barley farmer living in a community of thousands of other barley farmers is unlikely to be the founder of a lineage that is detectable later in genetic studies within that population. Instead, such a population would result in thousands of unique mutations that were relatively equally dispersed through it unless such an egalitarian social order could be maintained for very long periods of time.  

In real social orders, such egalitarian structure is rare, and over time, the yDNA of socially and economically dominant male lines would tend to spread with greater numbers than would that of others.

Of all the many thousands of genetic branching events that might potentially occur in a population, only a select few would tend to persist disproportionally within that population, and that persistence would tend to be due to some difference in the social status of those individuals.  It might also relate to how mobile a population is.   A clan of closely related men moving into and militarily conquering a region would almost certainly establish a genetic legacy that marked the moment of that historic event.

The further back in time, therefore, the more likely that a branching event occurred within the context of a powerful male lineage than a more common one.  Such men can be thought of as founders of lineages that out competed other lineages at least long enough to become so well distributed within a given population that their Y-DNA survived to modern times to be detected in genetic studies.  

When examining Y-DNA trees, each branching event was most likely to be the genetic footprint of someone of significant historic importance and therefore probably someone referenced either in historic records or associated with archeologically traceable cultural processes, i.e., more likely to be the guy living on top of some ancient hillfort, controlling resources and trade routes, than the guy toiling away in the barley fields below.  In fact, each of the barley farmers below might be highly motivated to have one of his daughters married off to some member of the family living on top of the hill, or at least allowing them to be sexually available to the male members of such a family.   Having a member of the hill top family, even a bastard line, counted within your own family or community would have its advantages in such a society.

Each branching event therefore serves as a kind of historic marker.   There is almost certainly a close association between y-DNA branching and historic processes.   The DNA therefore can be thought of as a kind of map of history.

It is not at all invalid for every man alive today to claim to descend from a powerful king or warlord of some kind.   We almost all certainly are if we go back far enough.  But the closer in time you are to such a branching event, the less likely it is that it represents anything historically significant.

Of course, it should also be observed that it was the greater numbers of more common people who were actually providing for the power and stability of these elite families.   Without the multitudes of commoners, there would have been no opportunity for the Y-DNA of the rulers to selectively proliferate within a population.  Such events should be thought of as reflecting an entire community of people not simply one male line.