Could 2 People Actually Repopulate Earth 

If their children, instead of paring off, mated in a matrix, with each male reproducing with every female (and vise versa), after a few generations there would be huge matrix of combinations. There would, of course, be a lot of genetic problems, but there would also be a large number of viable offspring. If the problematic people didn't reproduce, there would eventually be large, genetically diverse and stable population.

I've always wanted to know the answer to this question for at least 10 years. Excited to hear your response!

Elie, Aden, Carl, Asher, Sebastian all start with the same letters as Eve, Adam, Cain, Abel and Seth Nice detail

This was a very informative "what if" scenario. I do wonder why you didn't take into account how hard pregnancy and birth can be on the body. Without doctors/nurses/midwives, what are the odds Ellie would've been able to survive having so many children?

I remember hearing about a town in Italy, Stoccareddo, where almost everyone has the same last name, Bau, and most likely everyone is related. Almost everyone has red hair. They also eat extremely high fat foods and high sugar foods but have a very low occurrence of heart disease and diabetes. A majority of the population lives well into their 90s and 100s.

As a practical matter, the answer is no. You need a minimum number of people to maintain enough genetic diversity to avoid long-term problems (something called "the founder effect" or a "genetic bottleneck" in Biology). I've read that that minimum number has been estimated at around 50,000 individuals. One of the reasons scientists are so worried about the cheetah population is that, not only are their numbers low, the species shows indications of exactly this sort of a troubling lack of genetic diversity.

I'm reminded of the "Dark Eden" trilogy by Chris Beckett. The setting is a world populated by the descendants of two stranded astronauts - the technology level is essentially stone age, but a few artefacts of the original astronauts are still kept as holy relics, various genetic defects are rife ("batface"/cleft palate and "clawfoot"/club foot in particular), and an interesting culture has arisen.

Ellie should've visited the nearest cryobank. Those robots can't have possibly targeted those before vanishing :)

Paradoxically, the answer to indreeding is redundant breeding. That was the case with small prehistoric isolated tribes. They knew no contraception, had many babies, and many of them died from inbreeding burth defects. But the ones who randomly had good genetic combination, survived.

So basically it'll depend on how genetically gifted the two last people on earth are? If both have an incredibly tiny portion of negative genetic mutations, there would be a higher probability of things working out. If both were genetically perfect (is this even possible?), Then I can imagine things working out with quite a high probability.

First the poor Ellie would have to survive childbirth / labor, hoping the guy who survived has good skills as a doctor and will not make her pregnant every year or she will die before she can make enough babies to worry about inbreeding.

"Thankfully, they lived in Los Angeles, California" Don't need to watch the rest of the video to figure out the human race is doomed in Aiden and Ellie's hands.

As far as small gene pools are concerned, cheetahs are thought to be one of the smallest. DNA studies show that they may have about 70,000 years ago cheetahs been reduced to maybe as few as 4 animals. They are so genetically identical that all cheetahs are virtually brothers and sisters.

“carl accidentally killed Asher while fighting over toys” cain and abel flashbacks

I love how that brief aside about one of the children murdering each other just plays out in 5 seconds and is quickly glossed over.

Wow that was brilliant!! what a lot of research and graphics you have done - thank you.

This dilemma forgets to include issues regarding the risks of childbirth. Without functioning hospitals, and no nurses or midwives to assist them (presumably just the husband, a baby delivery guide, and whatever pain relievers they could scrounge up), the woman could have a much higher risk of maternal and/or infant mortality. Obviously it's doable, our ancestors were able to have kids without modern healthcare. But each time she tries to give birth, she's potentially gambling her life or the infant's life. For comparison, in England and Wales in 1895, the maternal death rate was roughly 650,000; globally in 2017, it was a little under 294,000. In ancient Rome circa 200 BCE, the infant mortality rate was 30%; globally in 2017 it was 2.9%.

I can tell you of a bird that was reduced to just one female. The Chatams Islands Robin. In the late 1970's it became critical. By the time it was attempted to try to save the bird there were two females but then one died without offspring leaving just "Old Blue" and a handful (single figures) of males. But the old girl with help did it and produced offspring. Today there are maybe 300 birds all directly descended from "Old Blue".

Didnt even realise 13 minutes had passed. Great cider man👍

Ellie should just become a genetic scientist and check for the DNA of their offspring and those with "problematic" gene poles are paired together with those with more favorable gene poles. With this method she could breed out most of the problematic genes while endorsing the favorite ones.

I've always wanted to know the answer to this question

Deadass props to the writing team. You guys always got some crazy creative stories I wouldn’t think of in a million years.

6:20 i come home after having biology class and this is what im greeted with...

In the case of Adam and Eve, it is assumed that they were created "perfect" and didn't have any negative genetics. It took several millennia in a fallen world for genetic mutations to manifest in humans to the point where they are today.

If I were in that boat, I'd be scouring the empty earth for some stored seed. There could be a single Eve, but many Adams that way. Frozen ova are also a thing, which would greatly improve the odds, if they could be found. That said, teaching myself how to perform the necessary procedures would be a challenge.

Finally the question we’ve all asked but never really thought much of. I love this channel ❤️

​ The two remaining surviving humans in the scenario could manage to gain the necessary extensive knowledge of CRISPR-Cas9 genome manipulation and editing , which could enable them to conceivably render any detrimental issues related to inbreeding in their grandchildren and subsequent generations pretty much moot.

i love that the writers came up with an interesting story rather than just listing facts they found off wikipedia. big props to everyone that worked on this video :)

My advice for these two is start traveling as quickly as possible and find those survivors, don't assume they're the only ones left! If that fails, have those kids start learning genetic manipulation right freaking now. You've got to start saving genetic samples from the dead and maybe in a few generations you'll have figured out how to artificially inseminate using unrelated DNA.

thank you for video I was feeling kinda down and now no longer frown.

Very interesting. As far as Ellie and Aiden vs Adam and Eve, consider that genetic mutations occur over time (mentioned in the video), and that recessive, bad traits can hide in a population (also mentioned in the video), but the farther back you go (say 250 generations or 6000 years) there would be significantly fewer recessive bad traits and this whole scenario becomes a LOT more possible. Bottom Line: what is true about inbreeding or genetic likelihoods TODAY is NOT true of 6000 years ago. Yes I am talking about Adam and Eve.

I see what you did there. 5:30. Aiden = Adam. Ellie = Eve. Carl = Cain. Asher = Abel. Sebastian = Seth.

Finally! The question we all must know

I've always wondered that if this happened, all the science and math we created, would be all gone.

What he forgot to mention is that Adam and Eve’s genes were perfect and those defects in recessive genes were “added” with time, through many generations. Kinda like what happens when kids play a game of telephone.

Idk where I heard this, but someone told me in order for 2 people to be able to repopulate, one of the sons would have to have a kid with the mom and the father would have to have one with one of the daughters. So that way instead of everyone being 50% mom 50% dad, you would have 2 different families. One that is 75% dad 25% mom and one that is 75% mom 25% dad, this apparently would allow for more mutation in the blood line very early in the repopulation process...

Were you afraid to mention the possibility of the parents having children with their children? Would that have possible good implications or only harmful to the genepool?

just adopt bro, it ain't that hard

"Evolution actually wants us to be attracted to people who are genetically different from us" To an extent, that's true. But studies have shown babies prefer their own kind, and couples tend to look alike, as well.

this video is so accurate that actually scared me.

what if he is gay

Watching Ellie and Aiden bob around non-stop leads me to conclude that they already have defects.

0:16, Correction, the bible does not say that God ONLY created adam and eve, rather there are verses that lead me to believe he was referring to them in plural, as in adam was his word for male and eve was his word for female. Either way there's nothing in genesis that says he didn't create anymore people. Besides, since God created space & time itself, with all the matter and anti-matter within it, what makes anyone think he could not and/or would not create more than just 2 people? **Edit:** Given that his own son is the word itself and himself incarnate it stands to reason that God is information itself, not just the words, pictures, sounds, etc that we use to represent it, but the very underlying concepts, history, future etc that have no tangible form to begin with. With this in mind anyone who is still refusing to believe God exists should think very carefully about where they expect to be after their flesh dies, the soul is a chunk of information and God being the entirety of all information that ever was, is and will be can do whatever he deems just/necessary with the information that refused to follow the rules/laws he identifies out of all his existence as holiest of them all.

The best way to increase their chances would be to do away with the idea of monogamy. For instance, ideally each of their ten sons would have at least one child with each of their eighteen daughters, with each successive generation similarly mixing and matching to minimize the compounding effects of inbreeding as much as possible.

11:06 "...she being the academic one and he being good with his hands." 💀

From memory, the Minimum Viable Population for humanity is about 2700 people, in order to have sufficient genetic diversity. 2 humans? That means no humans in the not too distance future.

Between 0:30 and 1:00 is spot-on. It probably SHOULD happen.

The greatest challenge for two people in this hypothetical scenario would be the fact that there are no experts they could contact on any given topic from agriculture, mechanics, electronics and most of all medicine. Any kind of emergency (child birth complications, natural disasters, heart attack, nuclear meltdown) would be catastrophic.

You need to turn this into a story-based series! I'd watch a whole season of episodes detailing the generations of Ellie & Aiden's successors and how the plan goes.

They have been lucky from the start as being the only two people on the fast expanse of Earth and still, both living close enough together to meet up.

The Cain and Abel reference made me lol

I'm surprised Ellie made it to 93 with all that stress. Plus being the only mother. Plus giving birth that many times.

Maternal and infant mortality would be a huge hurdle. Things that would be considered minor complications with pregnancy or labor could become life threatening and lower the gene pool further.

The second generation would have a high mortality rate having only siblings to mate with but as long as theyre careful keeping track of who the cousins and siblings are the third generation would end up doing far better. By gen 5 assuming nothing else in the apocalypse kills them thered be plenty of genetic diversity to bring the death toll down.

The case for the historical Adam and Eve is actually pretty strong from a genetic standpoint. See William Lane Craig’s work on the subjectS

I think you guys missed an important thing. Spermbanks. If they find one before they could spoil without refrigeration. And somehow get power running with some gasoline generators. Could they refrigerate enough for generations to come?

the best thing to do at that point is to just live your best life with no stress. marvel as nature takes back the concrete jungles, live in the penthouse of the tallest building and watch the sun set on a new chapter of earth's life.

I wonder if external, observable traits would be a clue to how genetically similar people are overall. Like, would it increase the success rate if they encouraged their children to "reproduce with a sibling who looks as different from you as possible" (eye color, hair color, etc.)?

Its possible but would be insanely difficult and of course mainly filled with alot of problems for the first 10-30 generation before anything stable happens

8:13 "Heart the size of a peppercorn." That *HAD* to be an exaggeration.

Wouldn’t travelling across the world through different environments and climates, different diets etc., encourage more genetic mutation and therefore diversity? At least over time. Just a thought

Fun thought experiment! You habla for sharing! Some important differences from the biblical story, though, so not really viable as an analysis of its plausibility. But still a fun watch!

Anyone else notice? Aiden - Adam Ellie - Eve Carl - Cain Asher - Abel Sebastian - Seth I noticed when Carl killed Asher in the story for no reason 😂

What if we assume that our two survivors had best the possible genetic makeup. No deadly or disabling genes and resistance to all deadly diseases. How long could humanity hang on with only these two?

Yeah, wouldn't want to have to know how this would really play out. Imagine matchmaking your kids and grandkids to "butter the muffin" with each other

In india, our religion has a system of planning marriages based on a factor named _Gotra_ (गोत्र). It is given to a child from the fathers. When planning a marriage for 2 people, we compare the _gotra_ of their grand mothers, and both parents. If anybody share their _gotra_ with the other, the kids of the couple will be not normal. _This is approximately what I remember from old family talks and experiences_

Wow, didn't know they Kurzgesagt in America! Thanks a lot for vid! =D

It was interesting to watch! Thanks!

Of course they can if we are talking about repopulating abominations of SCP instead of humans.

Plot Twist: Aiden was the one that created the AI because he wanted to be with Ellie and the best way to do it was to eliminate his competition.

Summary: yes but earth is now Alabama

I had no idea you could make an entire "scientific" video based off of fiction and what-ifs. Truly enlightening watching this fantasy play out in the pre-ordained manner of these creators. Thank you for sharing your insights into how you view science, genetics, and mutation. A valuable gift to be passed down for many years, never to stray from its initial beginnings or original genes. Sci-fi is such a broad and dynamic genre, kudos for finding your niche and staking your claim and never moving a meter from its genesis.

Yes, but at some point (probably pretty quickly) you would encounter the "inbreeding" problem. This obviously assumes that the two people can pro-create in the first place. So I guess the short and quick answer is "yes" but you would potentially have a population of people with at least some sort of growth defects since they would all be from the same parents basically.

Carl is Cain. Asher is Able. Sebastion is Seth. I see the Adam and Eve connections you're making.

One thing left out when talking about the garden of Eden is that Adam and Eve and their offspring lived very long lives. It wasn't until the great flood that mankinds life was drastically cut short. So if people lived near a millenium then it would be more probable then with people who, if lucky, could only live a century.

If you're wondering about the Garden of Eden scenario, remember they lived around 700 years old then. It could be that the first time around the Genes we're cleaner and stronger. Whereas trying to do this again now, you'd be starting with the handicap of a greater history of less than describable mutations.

I love how quickly this turned into a biology lesson

It could work, for maybe one generation or so. After every generation after that, you had better be ready to start listening to banjo music.

As an interesting addition to this, consider if the super-AI had run the DNA of everyone on the planet and had CHOSEN specifically the two individuals it was going to leave to repopulate the Earth - and thus could assure that, at least in the first generation, not only a complete absence of genetic overlap between the two but also an absence of genetic disease (both recessive and dominate). You are still going to have a lot of similarity in the first generations, but with the negative traits having to wait for natural mutation to enter into the system they would enter alongside the natural diversification. You cannot compare a scenario based on chance (the one above) to one based on intelligent design (AI intentionality with vast understanding of DNA and genetic disease along with the capacity to select for an optimum starting pair). That "clean start" could easily cover dozens of generations with distinct advantage over the genetic lottery.

In medevial Europe, the dangers of inbreeding were very much known and it was hardly ever done “to keep the bloodline pure”. It was always avoided unless really necessary for politics

Charles the second of spain: "Mummy says it’s a strong chin for a strong boy!"

I think the most incredible aspect of this story is that Ellie survived giving birth to 28 children.

Really enjoyed the video. In the Bible story 2 things are different. The first of course, being no genetic abnormalities to pass on since Adam and Eve are assumed to be as nearly perfect as possible. The second is life expectancy from 700 to 900 years, which means that no children children who know each other or were brought up together would have to mate.

Long ago, a chimpanzee had a mutation where two chimp chromosomes combined into one with a mid-telomere fusion. That's why humans have one fewer chromosomes than chimps; What was once two chimp chromosomes became one human chromosome. If you use an indicator dye to reveal the telomeres in the chromosomes, you will see one human chromosome with this mid-telomere fusion. The children of the original mutant chimp made babies with chimps and the fused chromosomes they possessed survived and became stable. Early in the process, these early humans could breed with a chimps and produce a human offspring. When the egg's DNA and the sperm's DNA met, the human DNA formed an organizational template where the chimp chromosomes could combine to create the mid-telomere fused DNA of the human being. The human DNA elevated the chimp DNA somehow. The resulting babies were early humans with one fewer chromosomes. Eventually, there were enough humans to breed with each other and a unique line of human beings began to diverge from the chimp populations. Having the linked chromosomes must have given our earliest ancestors some kind of advantage. In time, we leveraged those advantages to become the dominant species of animal on the planet.

"You were so preoccupied with whether or not you could, that you didn't stop to think if you should."

Sad thing is most likely there were way more survivors in this story but no one has a way to communicate over mass distances. It's like how in the walking dead you can only communicate and establish relationships with those you meet along the way.

i play enough niche: genetic survival, to know that you at least need some additions to the gene pool to properly survive. but i’m gonna test out this concept inside the game.

Will it be good to change the geographical area. As we know our surroundings affect our our living , lifestyle and thus it should have some affect on our genetic makeups as well. Therefore , they could create slightly diffent characterictic siblings and this small change could be a big change in the future .

This was actually WAY MORE interesting than I even expected! It’s a really crazy extreme view into the nature of biological evolution and how “Nature always finds a way!” ⭐️⭐️⭐️⭐️⭐️

“carl accidentally killed asher when fighting over toys” let me guess, carl was jealous that asher had better toys

Quite possible as has been shown with a number of species that were on the verge of extinction and with only one mating pair available. From that pair, scientists were able to revert the extinction event and even remove the species from the endangered list. Naturally this will cause a huge problem with genetic problems, but in the end the species would adapt to that as well.

I remember hearing about a species of cranes that went as low as about 15 breeding pears and now there are many of them now. I also heard that, about a couple 100,000 years ago, the human population dropped to a few breeding pears. Look at how many humans are on Earth now.

2 questions, 1. Would the outcome be better or worse if the breeding was cross generational? 2. How many generations on could we tell that there was a bottleneck like this?

An important difference between this scenario and the Hapsburgs is that in a survival situation the individuals that lack fitness don't survive long term. The Hapsburgs (and all inbreeding rich and powerful) were able to survive despite their genetic problems and so those problems were able to concentrate.

6:21 We're literally learning about this right now in science class (8th grade)

"starstruck lovers adam and eve" wasn't eve just made with one of adam's ribs when he was just sleeping one night?

I enjoyed the subtle nod in the naming conventions of Aiden and Ellie and their accident prone sons Carl, Asher, and Sebastian

Actually if the breed a lot ( let's say each of the 10 male grandkid has 2 kids with each of the 18 females grandkid leading to around 360 kids) no imagine even as high as 95% of them die before they are old enough to breed around 18 kids still survived(considering they survived they have a lower chance to have a recessive genes as the ones that did most likely died, you know natural selection doing it's thing) let's say they weren't super unlucky to all be of the same gender so they can still breed ( I am gonna assume 12 males 6 females in case they are a little unlucky) if they all once again breed a lot ( each males has 2 kids with each female so around 144 kids) now let's say this time a lower portion of them die because as I already mentioned their parents were less likely to have bad genes ( let's say only 50% die, lol I just realised most of them would have to see hundreds of deaths) so around 72 survive long enough to breed. Let's say they aren't super super unlucky and all 72 are not the same gender( the chances of that happening are too low) I am assuming around 30 females 42 males ( so once again lot of breeding and you end up with around 2520 children out of which around 1260 make it to breeding age) At this point, they should breed (over 420,000 kids)and then spread out into 4 to 5 groups so that when they all adapt to different surroundings the groups slowly become more distant allowing for genetic diversity So, yeah they can do it as long as they breed alot and aren't super unlucky.

This gave me a whole new understanding of wrong turn

Simulating Genesis also has to account for the part of the story where humans reportedly lived for almost 1000 years and began with zero genetic defects. Perhaps what we think of today as “normal humans” would be considered as severely deteriorated by the original humans. Our genetics got worse as our population got larger, until a balance point was reached.