What is the minimum number of people required to keep humanity as a species alive?

Question

I heard that at some point, a population of humans would die off due to a lack of genetic diversity. Where is that point?

Answer 1

This is simply not true.

No amount of lack of genetic diversity is lethal unless the lack restricts you to a lethal disease. Obviously if the only two people left on have a horrible genetic disease that will kill them before they can have children or otherwise limit their reproductive success, then yes, THAT will be fatal. But you could just as easily say it was the disease which killed them, not the lack of diversity.

Suppose the opposite example. Suppose that either through genetic engineering or eugenics somebody comes up with a male and a female with the most ideal DNA that can be contrived. Are they doomed to extinction? Hardly. They'll probably be better off in the long run than we are.

Not to say that small populations are without risk.

One risk is genetic drift. If you have a really small population, one mutation can affect as much as 50% of the population. Since most mutations are not good, the smaller your population is, the greater risk they are at that something bad will happen to them. Likewise, if a group of people all have characteristics that are very different from us, they might not really be considered 'human' any more, but instead something else.

Another risk is that of accidents. If you only have two people and a tree falls on one of them, your population has pretty much had it (unless, by some freak circumstance, the surviving member is a woman with an unborn male). A large population can brush off even major distasters, but they are much more major for small ones.

Curiously, another risk for a small population is gender. There is a chance that all the children born in a generation are one gender, thus drastically inhibiting the chances for a generation after that. This has already happened to several species where the only known surviving members were all of one gender.

Which brings us to the last caveat. Obvious, ANY number of people will fail to keep humanity alive if they're all of one gender. If a disease wipes out every woman on the face of the Earth but leaves all the men alive, then even three billion men will fail to perpetuate the species without some clever medical tinkering.

Answer 2

I believe a group as small as a few hundred could re-populate the species...
Humans will not die off due to lack of genetic diversity...

Answer 3

It will die when women or men become infertile. Then there is no way of producing anymore humans. But this can be countered with the development of test tube babies where babies are grown

Another reason might be that a bacteria will wipe out all humans, but again this can be countered by developments in science to counter it. Basically I don't see humans dying out. But you never know, we could kill the planet and therefore we all die and nothing can be done to stop it.

But say if everyone die and a couple of people are alive, you basicaly need two people. A male and a female. They could potentially be bother and sister and they can still reproduce, even though the chances of an abnormal baby is high, say a 50% chance I guess...

Answer 4

Typically, worldwide on average, a couple has to produce 2.1 children to replace themselves, allowing for infant death. Italy and Spain are only averaging 1.3 children per couple, Tokyo and Hong Kong are only at 0.98. The U.S. has an average of 2.03, figuring both native born and immigrant born children. These figures were in a article in the Smithsonian Magazine, to which I subscribe. I doubt that humans would die off due to lack of genetic diversity, but sometime in the future, there will be no caucasian, or African-American, or Asian or African, there will be just Earthlings.

Answer 5

only 2,1 male and 1 female.3 or 4 females and 2 males would be better but we could survive and repolulate on just the 2.

Answer 6

I think that we could survive if there is only two of us left
(mail & female), but that means HEAVY incest...
(like Adam&Eve's children)
Genetical research showed that we all (all humans alive) have ONE mail ancestor, a few tens of thousands years ago...
They call him Adam.

Answer 7

See "Minimum Viable Population" [MVP] in Wikipedia.

Answer 8

1 man + 1 woman = 2 people. The man has a penis and a scrotum full of sperm. He sticks his penis in the woman's vagina and rubs it until sperm discharges into her. The sperm fertilizes the egg. The egg becomes another human. Didn't you have sex ed?

Answer 9

2 a male and a female that is where we all came from isnt it?

Answer 10

just 2 healty with different sex is too enough to keep humans on earth