Sorry, this doesn’t follow at all. Of course of the people alive at any one time, some will leave no descendants. But we are not talking about some single individual European or African, but many thousands of them that would have interbred with Amerindians all over South America over the course of the past 500 years.
No one has ever said that it’s guaranteed; however, given history and population dynamics, it’s probable.
I have absolutely no idea, so I’ll take a guess: 1/e ~ 37%?
… and given sufficient time, the probable is inevitable.
I addressed this a couple of months ago back in Post #23:
So given enough time, yes, everyone alive will have European ancestors at some point in the future. No idea if 500 years is enough, but I’d guess that it would be. No population is truly isolated today.
Note that the wikipedia article I quoted earlier mentions isolated populations:
A mathematical answer isn’t possible without some knowledge/assumption of the family size distribution. If every person always has exactly two offspring, then 100% of the population at the identical ancestor point would have descendants left. If half of all people die childless but half have exactly four kids, and there’s no correlation between siblings on who’s in which category, then 54.4% would end up with no descendants, and 45.6% would end up with copious descendants. If 90% of all people die childless, and the remaining 10% all have 20 children each (again assuming independence), then it’s 91.8% who will leave no descendants, and 8.2% who end up being the ancestors of anyone. Obviously I’ve included some extreme assumptions, here, and the true answer will be somewhere between the extremes, but it’s hard to say where.
How did e get involved – did they mate on a natural log, or something? 
O.K. I decided to find some more solid evidence. Here it after some short searching.
#1 I read several articles on the North Sentinel Islanders with Sentinelese - Wikipedia as a starting point. Nothing in any of the historical accounts suggests they have ever been anything but extremely hostile to outsiders. No one has ever made contact. Extrapolate backward if you will, but it is documented that no one has interacted with the people there since records were kept, much less bred with them.
#2 Amazonian Indians: Evidence that there is not much “mixing” going on in certain tribes (as opposed to other Brazilians) as shown in the following research study.
http://www.funpecrp.com.br/GMR/year2005/vol2-4/gmr0122_full_text.htm
It’s titled “The mutation G298A®Ala100Thr on the coding sequence of the Duffy antigen/
chemokine receptor gene in non-caucasian Brazilians.”
The Amazonian Indians were included for comparison’s sake, since they were considered “unmixed”.
Here is the salient quote, it is not the main point of the paper, but provides background, extracted from a study written in 1988:
"For the Cayapo, the estimated admixture with Caucasoids was 0.002 [number of markers (nm) = 10; number of genes examined (ng) = 8,162] and with Blacks, 0.012 (nm = 12; ng = 10,652). For the Yanomama, the admixture was 0.000 with both Caucasians and Blacks (nm = 12; ng = 52,682 and 58,794; respectively) as estimated by Salzano and Callegari-Jacques (1988). Therefore, it is possible that in essentially unmixed Amerindians the T-33C GATA box or the C265T and/or G298A mutations are absent. "
The paper gives a little bit of background. The Cayapo are a bit less isolated than the Yanomamo were, but still with miniscule amounts of Caucasian or African admixture in the population that was measured by Salzano and Jacques in 1988. The Yanomamo, as of 1988, have zero. It is pretty unlikely, if zero markers were found in this population, that EVERY SINGLE MEMBER of the Yanomamo has a Caucasian or African ancestor as you insist. You probably are going to now say: “Oh, the Great White Ancester was there, but you can’t see him in ANY of the tribe, but EVERY LAST ONE of them was touched by him” but that assertion is just a case of the “Emperor’s New Clothes” to me.
Thanks for the interesting post, Rusalka. What you write supports my belief that trying to date the “MRCA of living mankind” is very problematic. One would have a better chance, perhaps, to estimate a pseudo-MRCA, ancestral to 99.99%, rather than 100%, of living humans.
It’s conceivable that the MRCA-date jumped from 4000 BC to 2000 BC when the last “pure-bred” Sentinelese died in the 2004 tsunami. Low probability, of course, but such jumps in the MRCA do happen, we just don’t know when and where.
On the question of Asian ancestry for Amazonians, I suppose there have been tiny migrations across the Bering Sea for millenia. Is it possible that these, rather than the Conquistadors, are the connection between the Asian MRCA and South America?
In North and Central America, natives began mixing with Europeans and Africans almost from Day One.
You make some good points, but you still seem to be laboring under some misconceptions.
It is certainly possible that there are isolated populations like the Yanomamo who are more distantly related from all other humans, and who may have no Caucasian ancestors. (Of course they have African ancestors, though–all of us do. That’s where our species originated, after all.)
However, you make too much with your emphasis on “EVERY SINGLE MEMBER.” If the Yanomamo do have any Caucasian ancestry (and I’m not saying they do), then assuming this ancestor lived in the time of the conquistadors, then it is likely that either ALL of the Yanomamo are descendants of this ancestor, or NONE of them are. After all, there simply aren’t that many of them, and by definition, they tend to mate within their own group.
As others keep mentioning, though, it’s not necessary for an isolated Amazonian tribe to have ever interbred with Caucasians to have Caucasian ancestry. For example, a conquistador could have had a child with a native, and the granddaughter of this union could have been incorporated into a neighboring tribe, and perhaps this girl’s daughter could have been incorporated into the isolated tribe.
So I am pretty much related to everyone alive 2000 years ago?
How long can genes last though? A piece of DNA contains a lot of information but their size is finite, thus the information they can hold is also finite. Which means after a while isn’t it possible these races will go back to how they were and have NO genes from any other race? I know the opposite is happening and should happen and is for the better but how long can a recessive gene last untill it gets bred out. Just because i have ancestors from X does not mean i have their genes right? Like if you have a black baby and from then on each generation only interbreds with white people. How long until that lineige is completely “white” with not black genes.
Someone tell Dan Brown … we’re all the last scion.
Genes are fairly persistent. All humans essentially have the same genes, and many of these genes are present in other species. For example, humans share over 98% of our genes with chimpanzees, and we have many of the same genes as fruit flies.
You actually seem to be referring to alleles, though, which are unique forms of a given gene. For example, a gene that affects eye color may have an allele that codes for blue eyes or brown eyes. Alleles can arise spontaneously by mutation, and can also disappear from human gene pool.
No. First off, many of the people alive 2,000 years ago have no living descendants today.
You are referring to what is called the identical ancestors point.
Change “2,000 years ago” to “5,000-15,000 years ago” and you are likely descended from every person alive on Earth at that time who still has living descendants.
Also, from the same link as my previous post:
In a nutshell? Pretty much. If you are asian, probably Ghengis Qan is in there somewhere. Us western Europeans are Charlemagne, Russians are Ivan the Terrible, Middle Easterners Mohammad or Timmurleng or one of the Great Moghuls [who are descended from Ghengis, by the way =)] Not sure about Africa, I have to admit I do not know enough history, but for sake of argument the Great King of Mali.
I can trace back dependably to the 1300s, but it is getting really tenuous in the 1370s and pretty much goes dead at 1302. We can sort of make educated guesses for another hundred years or so, but when church fires destroy baptismal records you sort of get screwed unless you can find legal proceedings and court documents, or at least church documents from other parishes.
I will jokingly claim descent on Mom’s side through Sigurd [of the Wagnerian opera fame] and MacBeth on my dad’s side [we are a from a very small and distant distaff clan, barely related but it sounds funny when discussed =)]
I find the whole I am related to <whomever> somewhat silly, unless it results in a title, crown or folding cash.
The Great Moghuls (the Timurid Badshahs) are descended from Timur the Lame. They also claim descent from Chinghiz Khan, but there’s no independent confirmation of that.
Actually, no, as **robby **already pointed out. Many people alive 2,000 years ago left no descendants alive today.
Genghis Khan had a practically super-natural log, which his concubines mated on.