Eli5: Could two people repopulate the earth on their own?


Just having an argument with a friend

In: 4

Sort of? They could start to repopulate the earth (depends on what pop level you consider “repopulated”) but with that little genetic diversity, it wouldn’t be long until they ran into problems associated with recessive genes coming out. Historically there was the famous Habsburg dynasty that suffered physical defects due to excessive inbreeding to the point where they could not live normal lives.

So basically, your new Adam and Eve would be fine, their kids would be fine, but their grandkids might start having issues, and their great-grandkids would almost certainly have serious issues.

Yes, they could, but there would be inbreeding issues, including the possibility of reinforcement of genetic weaknesses.

A search shows that there is no real consensus as to how many people would be ideal to ensure genetic flexibility and diversity, with figures ranging from 50 to over 10,000 people.

Essentially, the more people you start with, the better the chance of long term genetic security in the resultant population.

One pair of lobsters invasively populated an island to thousands of lobsters in the early 20th century, but scientists think that it would take 50 breeding humans to provide sufficient genetic variety to survive, and more like 500 breeding humans to adapt.

[Sauce. It’s a good read.](https://www.bbc.com/future/article/20160113-could-just-two-people-repopulate-earth)

No, they can’t repopulate the Earth. They could maybe go for a few generations but there’d be so much inbreeding that the species would be 100% non-viable and would die out pretty quickly. You could _not_ recreate the entire human race from two people.

No. People have a lot of different kinds of traits they can pass on to kids. Those are called genes. There are dominant genes–ones that tend to manifest over others, and recessive genes–ones that don’t unless the only option from both parents are recessive genes. A lot of really bad diseases are carried as recessive genes. That’s ok when you have a lot of genetic variation because those just get hidden by the dominant genes. When you shrink the gene pool to only two people, though, suddenly those recessive genes are way more likely to get passed on to later ancestors, since there are only a few options available. The first couple’s kids might be fine, but their kids would have a much higher incidence of recessive genes.
As a result, the population begins to have all kinds of genetic defects. Those just get worse without genetic variation and the population probably dies off. There’s no agreement on how many sets of genes humans need to survive, but most would say it’s at least 50 people and probably more like 1,000 or so.