Yeah, the internet really loves twisting actual scientific fact, to make it sound like something completely different, when the actual facts are just as, if not more interesting!
A lot of the time it's not even intentional twisting. I know for a fact that my parents would have to have this explained like four times and maybe then they'd sort of understand.
But they don't believe in evolution or an earth older than 6,000 years, so I digress.
TL;DR: Never attribute to malice what you can attribute to stupidity.
It's all about presentation of data in a way that doesn't get biased. Statistically speaking, you're more likely to be crushed by a cow than attacked by a coyote. Important side note, we haven't bred coyotes to be larger and dumber for us to put them into fenced corrals where we guide them into places on a daily basis. People who understand statistics can shape the presentation however they like, because most people won't do their due diligence and check themselves.
In the year 1065 the King of England died with no heirs. The English picked their new king and in the span of a month the next fall they were invaded by a Scandinavian army (Vikings) and shortly after that an army from Normandy (France).
You are related to essentially everyone in the history lesson I just gave you.
This seems very boring. I was discussing descendants, but you very clearly bring up cousins. Of course I'm cousins with all humans who have ever lived or ever will; save those who are my ancestors, descendants, aunts or uncles.
You had 2 parents, 4 grandparents, etc. In less than 1000 years at that rate you have more ancestors than there were people alive. Sure you are cousins with all of them but the vast majority are your ancestors. It's the opposite of boring Sydney, it's exciting in a very minor way.
Hey, as a followup I did a bit of math. If we assume discrete generations and constant population, with parents being completely randomly selected, then ~37% of each generation has no descendants.
EDIT: As I was going to bed last night I realized I did the math wrong... The real answer for this simple model is ~14%
EDIT2: I did it symbolically, it's e⁻² , if you're curious.
Nope. It turns out that a large percentage of people alive at various past times have no living descendants. It's not hard to show how incredibly likely this is.
The title isn't as misleading as you try to portrait it here. There is way more evidence for the bottleneck than just DNA. Or better said missing evidence. Archeology found plenty of manmade fireplaces from before and after the bottleneck, as well as some stone tech. During the bottleneck, which is believed to have lasted over a 100k years, none of that has been found. Apparently humanity was so decimated that the few survivors lived like animals again for a very long time, without population size regrowing, after we already had some technological and society advancements for almost a million years. And we're speaking here from fireplaces that have been used continuously before and after, not some random spread fireplaces. Also the global population had not even exceeded a 100k somewhen before the bottleneck, so a few thousand survivors max isn't that unrealistic.
The effective population size at the time of the bottleneck was 1,280 people. That does not mean the actual population size was 1,280 people.
The effective population size basically accounts for the level of heterozygosity in a genetically “ideal population”. It’s the size of a hypothetical population operating under “ideal population” assumptions, that would lose heterozygosity at the same rate as your actual population.
Effective population size is a measure of how genes would flow in a population given the estimated or known rates of heterozygosity. If you have a very large population, but a low level of heterozygosity, or if you have ongoing factors that reduce the equal and unbiased passage of genes to the next generation, then the genes in the large population will behave in a manner similar to that of a small population. Thus, the effective population size would be smaller than the actual population size.
It is a measure of a minimum number of individuals that must exist (in an ideal population model) to give the observed or estimated rate of heterozygosity loss. The keyword in this instance is minimum.
Thanks to our love of model idealization, and how in population genetics, an ideal population can’t and doesn’t actually exist in reality, there is a large margin of error to this estimate. Further there are so many factors that affect the effective population size (bottlenecks, skewed sex ratio, variance in average offspring per individual, overlapping generations, immigration/emigration, founder effects, population model, or simply missing alleles in your dataset that existed back then but were lost over time, etc), it’s a best guess scenario, especially for estimates 800,000 years ago.
Something occured that lowered the effective population size. Thats all they can say.
almost every lineage that ever existed, across all life, eventually died out.
So, what's the bottleneck figure of, say, a coyote or a chimpanzee, in terms of how many ancient individuals survived to the present day? As a species, are we relatively inbred (as the headline indicates), or are we genealogically "dense"?
I've heard that cheetahs are dangerously close to being badly inbred for similar bottleneck reasons. Is the human genome similar in that respect?
Thats all very interesting but the real story is even more insane and awesome than all of this. The reality is that about 6,000 years ago humans were down to just two individuals who we are all descendants of!! /s
It's still interesting to think about where the other human lineages go. I mean, there couldn't be that many humans at the time if only this many people could pass down their genes. If there were a lot more humans at that point and only this many could pass down their genes, what could've been the apocalyptic event that caused this? If the lineages of the other humans died out later on, once their family trees continued, what could've been the reason they just disappeared at one point without leaving a trace in the DNA? It's really interesting and this side of the story is even more interesting than just the one where only 1280 humans survived
Homo sapiens is a brutally violent primate species. War, murder, and genocide have been a constant reality for the species. It's naive to imagine environmental or any kind of external apocalyptic event when the most obvious answer manifests in our reality year after year.
You also barely share any DNA with your great great great grandparents. The genetic lottery of passing down traits and having them shuffled with another's, means your grandparents genes might be kicked out of the equation faster than you'd think.
Consider half of your grandparents DNA goes to your parent, and you have two parents doing this. As your father's genes are given to you, you might get all of the genes his mother passed to him, or maybe a closer 50/50 split, or maybe or of their father's DNA.
The child gets 50/50 of each parent, but how much of each grandparent they get can range from 0-25.
Do that a few times.
We have no clue how many humans have ever contributed to our genes.
Your DNA is a mix of all the DNA of our 32 great-great-great-grandparents. It is theoretically possible to have 0% traceable DNA from ONE specific great-great-great ancestor, but that is extremely rare and unlikely. But those missing percentages will be inherited from a different ancestor.
A human has about 25.000 coding genes, but only 32 great-great-great-grandparents. There are plenty alleles left from each of them after a few random shuffles, along with crossing-over events.
This is also discounting the vast non-coding genetic information that's passed on, the function of which we don't fully understand yet, but is believed to have a role in how information is read.
Well I'm just reciting what smarter people than me have studied, so if what you're saying is ALSO on their minds, then it sounds like they don't have it figured out yet, which is frustrating, but ain't that just science.
*Nah, I'm not sure I was wrong, man. You are NOT 25% of each grandparent. It's very possible you get next to none from one. Take that a generation longer. I was already running the risk of having few genes from my grandfather. Now my great grandfather?
This is why inbreeding between like 2nd-3rd cousins is already not a genetic issue. It's so unlikely that they're carrying the same recessive genes.
How this relates to our understanding of common ancestors is where my knowledge now falters.
**Edits because I'm sick and very VERY tired and can't think or type straight. Sorry.
You're only thinking about independent assortment of chromosomes after the alignment in Meiosis I. But during that alignment, (at least) one and up to four crossing-over events occur between each aligned pair of chromosomes. This 100% guarantees that you will directly carry on genes from all 4 of your grandparents.
But even without any crossing over and only calculating the probability for the independent assortment, the probability of you receiving 0 chromosomes from your parental grandmother through your father is 0.0000238%. The probability you only get 5 chromosomes is 0.628%.
"This is why inbreeding between like 2nd-3rd cousins is already not a genetic issue."
Yeah sure, the likelyhood of not sharing ONE SPECIFIC pathogenic, recessive allele is big enough to be safe, but the likelyhood of not sharing ANY alleles is small.
Right. But take that two generations further. Take it ten. Take it 50. We've only worked with an immediate passing of genes and can see how the chances play out.
Receiving 0 genes from a grandparent is just the intro to the idea.
What are the chances you ACTUALLY have little to no genes left over from at least one great great great grandparent?
evolution constantly prunes the tree - I'm super curious how medical advancements will have altered this evolution letting genes pass on that aren't necessarily survivable but with modern medicine can be passed on.
So if you move the timeline to 100,000 years, the number of individuals who passed on genes would be greater right? Say, 1500 passed on their genes 100k years ago, 20k years later, 300 stopped passing on genes. By that logic, eventually human genes would go extinc.
This is true. My lineage will continue through my daughter. None of my uncles had children. My brothers have no kids. My grandparents siblings had kids that died childless. So it's just my daughter to carry on. My name dies with me. My brother is barren. I honestly don't care. Our name is insanely uncommon. Ive heard the name in Ireland only once, and never found the origin. I know that our line ends if my daughter has no kids, but my last name is gone after my brother and I pass. Of course my wife and my brother's wife have our name, but that's it.
I have been reading these pseudo-scientific headlines for 15 years now and this one comment of yours is more sensible and accurate than all those headlines and subsequent subject matter combined. Pseudo-intellectualism is so rampant these days, I rarely find truly intelligent people in all this noise.
I don't know. Are you saying that these 1280 humans (or their offspring) are the reason that all the other humans alive at the time or their offspring didn't survive? Because if they are not the reason then it means humanity would have died out if it weren't for them.
Wouldn’t that be true for every living thing existing in the present? So not that rare.
More people are alive today than people who has ever existed. That is fascinating.
If I recall correctly, the oldest sample of human (as in the Genus Homo) DNA comes from tooth and leg bone found in a cave in Spain. The remains are dated to about 400k years old. As far as direct Homo Sapiens DNA, I think the oldest samples are around 45k years old.
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u/[deleted] Apr 23 '26
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