What Percentage of People from 300 Years Ago Have Living Descendants Today?

Great Debates
1

I purposely put this question in GD, as I don’t believe it has a factual (knowable) answer, but if the mods disagree, please feel free to place in GQ.

Every now and again, a study will come across the wires about how, due to population bottlenecks and pedigree collapse, we’re all related to each other and all descended from X number of men/women who lived at some particular point in time.

I’ve always been curious about the reverse of this… what percentage of people from any given point in time have living descendants today?

I understand that the answer will probably vary greatly depending on the particular point in time. I’m sure that the figure will be higher for more recent period and especially low in periods following large die-offs (such as the Black Death of the 1340-50s).

I’m not particularly attached to the “300 years ago” point in time - I chose it somewhat arbitrarily. If you can come up with an answer using a different time period, please feel free to discuss.

Zev Steinhardt

2

I only know of one, but that’s because I’m related to him. :smiley:

The Sears Family Associationhas the genealogy of the descendants of Richard Sears, who was born in Plymouth Colony about 1672.

3

I’m not sure how to answer your question, or if there even is an answer outside of simulation studies, but just to be clear, even in those cases some of the X number of people would not have living descendants today. Some would be infertile, some would die without breeding, and some lines would die out on their own.

There is such a thing as The Identical Ancestor Point where (again, this is from simulations) everyone alive at that time is either an ancestor of every living person today or of no one today.

4

One could only speculate because the numbers would be somewhat skewed due to a historically high infant mortality rate. I don’t think anyone can provide a definitive answer, but I will give information about my family to help someone be able to do the math.

In the part of my own family that carries my surname, I can only trace back 170 years. The mortality of children in my family was about 1 in three having not made it to adulthood in the mid-1800’s. There were ten surviving children in my earliest traceable generation and at least 2 more that didn’t make it from one ten year census to the next. There were almost certainly those that were born and died between censuses that I have no way to know about, also. Something else to consider: Even in modern times, about 50% of pregnancies fail before they are even noticed by the mother. I would imagine that number would be substantially higher in the past and some of that would have occurred in my family as well. So would they be counted as people in this? Or are you just counting people that were born alive?

My simplistic thought on this would be that every person born in a generation would have a bare minimum 50% chance of living to adulthood (either you do or don’t). Once in adulthood, a person would have a near 100% chance of marrying and having children of their own due to societal pressure in those times to do that. The number of bachelors and spinsters in my family is quite small; one bachelor out of 10 of the children I cited earlier.

Another side of my family is quite well documented as it was a big (influential) family back East. So much so that it merited a genealogy book to be written about it in 1903. The genealogy was traced back to a single Scottish prisoner captured by the British during the Battle of Dunbar in 1653. He was force-marched to the coast was sent to America as an indentured servant for the Massachusetts Ironworks along with the other 150 prisoners that survived the march. So about 300 years and nine generations later, my great-grandmother is listed as she was 10 years old at that time. She is one of 3000 documented relatives of this man as of 1903.

5

It would be possible to get a sensible number for this for a much shorter span than 300 years, I think - and also, I suspect that the percentage chance of having any descendants at X amount of time probably doesn’t decrease very much from about the third generation onwards. The reason being - once you have any descendants at all, the probability is that you have more than one, and it’s very much less likely that multiple ancestors of yours will ALL die without descendants, than that you personally, a single individual, will do so.

I did a quick BOTE simulation, with vaguely plausible simple numbers.

Suppose in your society, the chances at birth of a person leaving descendants is:

20% have 0
20% have 1
20% have 2
20% have 3
20% have 4
nobody has more than 4

(those numbers are obviously not drawn from real life, but they’re not awful - a distribution like that would lead to a population that doubled every 50 years or so so it’s slightly on the high side, but not too bad)

So an average person has an 80% chance of having at least one descendant in the first generation.

IF they have 0 children, they always still have 0 children in the 2nd generation -
IF they have 1, they have a 20% chance of having 0 in the 2nd generation
IF they have 2, they have a 4% chance of having 0 in the 2nd generation
IF they have 3 they have a .8% chance of having 0 in the 2nd generation
IF they have 4, they have a .16% chance of having 0 in the 2nd generation.

When I add all those numbers up, I find that Pr(0 in the second generation)=.21 + .2.2 + .2*.04+.2*.008+.2*.0016 ~=.25

So the probability of your random person having a descendant in the second generation is about 75%. It’s gone down really very little. It would go down even less in the third generation.

The question “how many people born in (say) 1700 still had descendants in 1800” may or may not be empirically determinable. But whatever the answer is, I believe the answer to “how many people born in 1700 still have descendants today” is probably more or less the same.

6

I don’t know the math, but found this article interesting.

7

Could we look at something like what proportion of signers of the Declaration of Independence have living descendants? That would be flawed because it is only men, and perhaps skewed upwards, because they came from the elite, but maybe it is a starting point.

8

I’ll start: 56 men signed it, including John Hart from NJ. My wife’s family are descended from him. He had 13 kids so that helped.

9

I’m descended form a signer. He’s one of only a few who signed all 3 founding documents, too (DoI, AoC, C).

10

John Mace and JXJohn’s wife are eligible to be members of this group :

An elite honor, it appears.

According to them, 15 of the 56 signers have no living descendants.

11

I am destined to be one of them who doesn’t. My three sons are all over 40, none are fathers and at that age, probably will never be.

It doesn’t bother me a bit. In fact, maybe a good thing, as I have hereditary bindness.