Another fun question! It certainly would be possible. The complications would depend on who the two people were, and how long ago the couple started out.
What everyone would be worried about, I think, are genetic diseases. Hemophilia was pretty common in European royalty. Around 1 in 20 Pingalese Islanders are severely colorblind (instead of the 1 in 20,000 everywhere else).1
Polydactyly, or extra fingers and toes are more common among the Amish of Pennsylvania due to a specific genetic condition.2Ashkenazi Jews have a higher rate of Tay Sachs and cystic fibrosis (CF).3
What do all of these groups have in common? Each started from a small group and there was limited contact with the outside world.
The result is a higher rate of certain genetic diseases. Why is this?
Recessive genes and the founder effect
Because each of us carries the seeds for at least 5 or 10 genetic diseases within our DNA. Most of us don’t have these diseases because we only have one copy of these recessivegenes.
What recessive means is that you need to have two copies of the disease version of the gene to get the disease. If you have a normal copy and a disease copy, you end up not having the disease. But you are a carrier.
And if two carriers have kids, then there is a 25% chance that the kids will have the disease. In a small, interrelated group, up to half of the people may be carriers. This obviously greatly increases the chances that carriers will meet and have kids.
This is called thefounder effect. When a population is founded by just a small number of individuals, the genetic diseases they carry will become much more common in the population. This is what happened to the groups mentioned above, like the Pingalese islanders and the Amish.
The flip side of this is that some diseases essentially disappear from the population. This is why it would depend on who the founders were. If they were disease gene free (which none of us living today are), then the complications would be minor. But if they harbored any recessive mutations, which most humans do, then genetic diseases might become a problem.
New mutations over time
All of these examples have not been going on for very long, on the order of a few hundred years or so. What would happen over thousands or even hundreds of thousands of years?
Well, it would all work out over hundreds of thousands of years certainly. Groups would split up, become separated, and form new groups. Each one of these would then have their own genetic baggage.
For example, if current theories are to be believed, our ancestors left Africa in waves over the past 100,000 years or so. Each of these groups was probably small and grew in isolation from the rest of humanity.
The result? What you see around you. Northern Europeans have a higher incidence of CF. Africans have a higher incidence of sickle cell anemia. Southeast Asians have a higher incidence of alpha-thalassemia.
If our original two people didn’t have these diseases, then where would the disease genes come from? Well, new mutations happen all the time. Most are harmless, a few are harmful, and a very few are beneficial.
With lots of people over a long period of time, some bad mutations are bound to develop. For example, we see them happening today in a disease called neurofibromatosis (NF). About half of all new cases of NF are because of new mutations.4
Evolution of human traits
What we’ve discussed for genetic diseases is also true for other things like genetic traits. Our ancestors in Africa were most likely dark-skinned with brown eyes. A group that reached Northern Europe developed mutations that gave blue eyes, red and blonde hair, and light skin.
These same mutations could have developed in Africa. In fact, they probably did but disappeared because people with fair skin may not have done as well there.
In Northern Europe, these mutations were actually beneficial (probably to get enough vitamin D from the sun). This meant that once the mutation popped up, these people did better and so eventually, most Northern Europeans ended up with light skin.
I could go on and on about this. Instead, let’s get back to your original question.
It certainly seems possible that two people could populate the Earth with minimal complications. That is, as long as they weren’t harboring too many devastating genetic disease genes and/or enough time passed.
FAQs
Is it possible for two people to populate the earth? ›
While it is theoretically possible for two people to repopulate the Earth, it would be extremely difficult and unlikely.
How many different people would you need to repopulate the earth? ›This means that, in a hypothetical apocalypse, humanity would need a lot more than a handful of survivors to repopulate effectively. However, to retain evolutionary potential – to remain genetically flexible and diverse – the IUCN criteria suggest we would need at least 500 effective individuals.
How many people would you need to repopulate the earth without inbreeding? ›So how much variety do you need? It's a debate that goes right back to the 80s, says Stephens, when an Australian scientist proposed a universal rule of thumb. “Basically you need 50 breeding individuals to avoid inbreeding depression and 500 in order to adapt,” he says.
How many humans are needed to continue the species? ›research on minimum viable population
They created the “50/500” rule, which suggested that a minimum population size of 50 was necessary to combat inbreeding and a minimum of 500 individuals was needed to reduce genetic drift.
So if everyone on Earth lived like a middle class American, then the planet might have a carrying capacity of around 2 billion. However, if people only consumed what they actually needed, then the Earth could potentially support a much higher figure.
How many people can populate the Earth? ›Estimates vary, but we're expected to reach "peak human" around 2070 or 2080, at which point there will be between billion and 10.4 billion people on the planet.
What was the lowest human population in history? ›A late human population bottleneck is postulated by some scholars at approximately 70,000 years ago, during the Toba catastrophe, when Homo sapiens population may have dropped to as low as between 1,000 and 10,000 individuals.
What is the minimum to repopulate? ›The rule of thumb used by conservation biologists is that it takes about 500 individuals to properly repopulate a species. You can preserve something with 50 individuals, but the species is going to radically alter in the process.
Can two animals repopulate a species? ›No. Because of the very likely possibility of inbreeding and inheritable genetic diseases, most ecologists and biologists recognize the idea of a Minimum viable population - Wikipedia .
How did humans reproduce without inbreeding? ›The results suggest that people deliberately sought partners beyond their immediate family, and that they were probably connected to a wider network of groups from within which mates were chosen, in order to avoid becoming inbred.
Who has the highest rate of inbreeding? ›
Consanguineous unions range from cousin-cousin to more distant relatedness, and their prevalence varies by culture. Prevalence is highest in Arab countries, followed by India, Japan, Brazil and Israel.
When did humans stop inbreeding? ›Early humans seem to have recognised the dangers of inbreeding at least 34,000 years ago, and developed surprisingly sophisticated social and mating networks to avoid it, new research has found.
What was the maximum number of human species that existed at the same time? ›Nine human species walked the Earth 300,000 years ago.
What is the rule of 500 in society? ›In societies with fewer than 500 people, he says, everyone can get along, but above that threshold, the bonds of kinship are diluted and the strong take advantage of the weak.
Will humans evolve into multiple species? ›The only realistic scenario for the evolution of two species out of ours would probably be if we expanded beyond our home planet and then lost contact with the settlers. If both populations survived long enough – much more than 100,000 years – we might see divergence and maybe two species of humans.
What is the minimum human population to repopulate? ›The so-called "50/500 rule", where a population needs 50 individuals to prevent inbreeding depression, and 500 individuals to guard against genetic drift at-large, is an oft-used benchmark for an MVP, but a recent study suggests that this guideline is not applicable across a wide diversity of taxa.
How long until the human population doubles? ›The world's current (overall as well as natural) growth rate is about 1.14%, representing a doubling time of 61 years. We can expect the world's population of 6.5 billion to become 13 billion by 2067 if current growth continues. The world's growth rate peaked in the 1960s at 2% and a doubling time of 35 years.
Is it possible for humans to exist on another planet? ›Essential elements of life- oxygen, water, air, etc. - are lacking on other planets. However, scientists are still searching to look for signs of life on other planets. Therefore, humans can survive on other planets only if they possess essential elements of life.
Is Earth overpopulated already? ›Yes, for two main reasons. First, people are rapidly displacing wildlife species across the globe, initiating a mass extinction event.