The widest point of the Ancestor Cone happens for most of us around AD , when our family tree is near the total world population at the time. From that point on, pedigree collapse becomes a stronger factor than the normal upward x2 multiplier, and the tree converges inwards. The simplest way to think about it is that every stranger in the world is a cousin of yours, and the only question is how distant a cousin they are.
The degree of cousin first, second, etc. For first cousins, you only have to go back two generations to hit your common grandparents.
For second cousins, you have to go back three generations to your common great-grandparents. Since a lot of people get confused about cousin definitions, I made a little chart illustrating what a second cousin is. So notice that for you and your second cousin, A your parent is a first cousin of their parent, B you have grandparents that are siblings, and C their parents are your common great-grandparents. For third cousins, everything just goes up a level—your parents are second cousins, your grandparents are first cousins, your great-grandparents are siblings, and you have a common pair of great-great-grandparents.
A straight second, third, or fourth cousin must be on your same generation level. The number of cousins you have grows exponentially as the degree of distance goes up. You may have a small number of first cousins, but you likely have hundreds of third cousins, thousands of fifth cousins, and over a million eighth cousins. Because I got a little obsessed with this concept while doing this post, I decided to roll up the nerd sleeves and figured out a formula for this:.
I calculated some examples below:. Most interesting to me is that these numbers go up so exponentially that taking the world average for number of children per family 2. The other way to look at this is from the top down and see how quickly the distance of relation is magnified as generations move down—while you and your sibling grew up in the same house, your kids will be cousins who might or might not be friends and your grandkids might barely know each other.
In its first couple hundred years, before expanding into the thousands, it might look something like this:. Little Telia, born right around the year , is as much a mystery to you as your ancestors from the early s up above. Wait But Why posts regularly. If you like this, check out Meet your ancestors all of them , Your life in weeks , and What makes you you. By providing your email, you agree to the Quartz Privacy Policy. Skip to navigation Skip to content.
Check out this graphic I made to help you visualize the number ancestors you have going back 10 generations. I hope that this post helped you learn about how many ancestors you have, pedigree collapse, and how this effects how many ancestors you have further back.
Confirmation Bias in Genetic Genealogy: Beware! This site uses Akismet to reduce spam. Learn how your comment data is processed. I wonder how migration affects these numbers. My parents families were immigrants to South Africa from different parts of the world Germany, Ireland, England not so far back. Would migration like that affect the rates of pedigree collapse, resulting in more ancestors? Or is it too small of a difference to be noticeable?
All French as far back as anyone knows. I find this all so fascinating. Hi Lunaris, Thank you so much for your question! My mother has family from a small town in Slovakia, and everyone there seems to be related.
This is similar to my husband's experience leaving a small town in Mexico. In their case, they both started families with people who were very unlikely to be related to them in any way.
It is such an interesting topic, you are right! Each parent in a direct line of ancestry had to have had 2 parents no matter who they were. I know it appears impossible to have that many people 67 generations ago, but someone had to produce the offspring in order for the line to continue, people don't appear out of thin air.
Stephen Wiles, Right, but if those two parents were, for example 4th cousins, they shared a common set of grandparents a certain number of generations back. Dear Mercedes, You have composed a brilliant article, above. So sorry but I found it to be a little sad. This is because you have stated that "pedigree collapse" is found in every family.
I think that "pedigree collapse" is the same as incest. Incest is quite negative. Incest can lead to mental retardation, in offspring. I feel worried that my ancestors indulged in incest. Is there not a better theory to explain numbers in our ancestry and exclude incest?
Alternatively, is it even true that incest with distant relatives is alright for the offspring to be fine biologically? Based on the table below, if you go back 40 generations, you have over two trillion ancestors! Of course, this number doesn't mean you have that many unique ancestors in 40 generations.
What is happening is repetition of ancestors, that is, the same ancestors appearing over and over again in a pedigree. Repetition seldom appears within the first ten generations, but the further back you go, the more repetition you are likely to find. As an example of repetition of ancestors, there is a famous pedigree that begins having significant repetition within the first few generations: that of outlaw, Jesse JAMES.
For those of you being autosomal-DNA tested e. Even at five generations, you are likely to have only 3. I'll know more about myself that way, than I do by the fact that I've bumped into a connection to Charlemagne la de dah. The greatly diminishing percentage of one ancestor's genes in your personal genome as you go back in your pedigree is just one reason why it's so biologically insignificant to have distant illustrious ancestors. Socially, culturally, and historically it may be very significant to you, personally, but not because you are any kind of genetic "image" of your ancestor.
It's also a cautionary as to why it's foolish to think you live on in your children. Your genetic contribution to your descendants diminishes so rapidly, the idea that bearing children gives you "continuence" is absurd.
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