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How Many Generations Back Are We All Related?

The idea that every human is related to every other human is easy enough to understand, in theory. But it leads to the question: how many generations back are we all related?

In other words, how many generations back would we have to look in everyone’s family tree to find the ancestor, or ancestors, that we share in common? In this post, you will learn the answer to this question, and more.

How Many Generations Back Are We All Related

To avoid confusion, I should start off by defining what this article defines as being “related”. We are going to explore genealogical relationships, which is different than a genetic relationship.

Since we (all humans) are all related to each other in some way, we are all distant cousins. Very distant relatives will generally share no genetic material, even if there is a verified common ancestor in their respective family trees.

The other definition that I’d like to set for this article is “we”. By “we”, I mean all of us – all 7.8 billion people in the world.

If we didn’t include every human in the discussion, and instead focused on smaller populations of people in specific places, we would not need to go as far back in time to find how any two given people are related.

How long ago was the common ancestor of all humans?

Many people imagine that the common ancestor shared between all humans alive today lived a hundred thousand years ago, or more. Many experts agree that this is unlikely to be the case, but there is no exact answer that is agreed upon by everyone.

The common ancestor may have been only 3000 years back

The most recent common ancestor shared between all humans alive today likely lived about 3000 years ago, according to one mathematical model designed by a professor at Yale University. If we assume 25 years per generation, then we could find the common ancestor for all humans about 125 generations back in our collective family trees.

The professor that designed this model took factors such as geography and the movement of people across regions. Even so, it is impossible to know that the estimate of 3,000 years is correct because it is impossible to prove or disprove.

If we all do really share an ancestor who lived about 3,000 years ago, we do not know exactly where this person may have lived, or who they were.

However, we can be sure that we all share common ancestors at some point because of simple math.

The number of ancestors that any person has doubles going back each generation. After 4 generations, we have 14 total ancestors, but in 40 generations, we would have as many as one trillion ancestors.

The only problem is that there have never been one trillion humans, even if we counted everyone who has ever lived. Scientists estimate that only 117 billion humans have ever existed.

It is impossible for all of us to have ancestors going back dozens of generations without having overlapping ancestors with everyone else, and even many ancestors occupying multiple spots in our own family tree. There simply were not enough people alive throughout history for all of us to have completely different sets of ancestors.

DNA can’t help us solve this

The current technology of autosomal DNA testing can’t help us determine how far back our most recent common ancestor might be. This is because we did not inherit autosomal DNA from all of our ancestors.

We are able to use Y-DNA and mtDNA studies to determine how far back shared direct-line male and female ancestors were for most people, but this only provides insight into a small percentage of our ancestors. One example of a shared ancestor between all humans is the theory of Mitochondrial Eve.

We did not inherit Y-DNA, mtDNA, or autosomal DNA from most of our ancestors.

However, we know that we had ancestors. We all have a family tree, even if we don’t know all of the people who are in it.

How can we all share a common ancestor that is so recent?

How could it be possible that every human shares a common ancestor that is as recently as 3000 years? Granted, 3,000 years is not truly recent in a genealogical sense, but it is very recent when we consider that the human species is a few hundred thousand years old.

People might mistakenly assume that people from vastly different geographic regions, such as completely different continents, could not possibly share a common ancestor from within the past few thousand years. Australia is a continent completely surrounded by water, and the Bering Land Bridge has been covered with water for about 10,000 years.

How could we all be “recently” related if our ancestors were geographically separated from each other? The answer is simple, really.

Our ancestors traveled more than we imagine

Modern people often imagine historic groups of humans as fairly stationary because travel was difficult, expensive, and dangerous. While it was all of these things, sometimes it was even more difficult, expensive, and dangerous to stay put.

Economic, political, religious, and even interpersonal circumstances caused individuals or large groups of people to travel from one place to another. Sometimes, this travel was temporary, but other times it ended up being for the long-term.

Human beings have been traveling by foot, using animals for transport, or navigating the open sea, for tens of thousands of years. There is even evidence that Neanderthals, who were “hybridized into non-existence” approximately 40,000 years ago, knew how to harness the technology of boats for travel.

Travel and migration merged our family trees

While there are many populations of people around the world that are very isolated geographically, all it takes it just one person from somewhere else to join the small, close-knit community.

After several generations, all of the descendants of that community now share the ancestors of the person who arrived from far away. It one takes one person to introduce the ancestors of an entirely different region into another.

There are likely to be exceptions

It is likely more correct to say that “most people” share a common ancestor within the past 3,000 years, give or take a few thousand years. There may be groups of people whose ancestors had no contact with people from anywhere else for many more thousands of years.

Many people likely share more recent ancestors

If both of your parents have ancestry from the place where you live, or have ancestry in the same part of the world, it is likely that you share a more recent common ancestor than the 3,000 year estimate in this article.

For example, it is estimated that anyone with European ancestry from the past several hundred years is descended from Charlemagne, who lived about 1200 years ago. No one knows for sure, but many experts believe he was born in Germany.

Everyone who lives in Germany with any European ancestor is likely descended from Charlemagne, but many Germans might also find that they have a more recent shared ancestor, too. This assumes, of course, that everyone knows all of their ancestors going back many generations, which most of us do not.


I hope that this article has been an interesting exploration into the quest for our common ancestor. Of course, this entire discussion, as fun as it is, is entirely hypothetical.

While I would love to be able to fill in all of the blanks on my tree going back thousands of years, it’s just one of those things that may always be impossible.

If you have any questions about something you read here, please feel to join in the discussion below.

Thanks for stopping by today.

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