Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Humans are more closely related than we commonly think

scientificamerican.com

Post reply on HN
Print view View original

21–30 of 142 posts

Re: Humans are more closely related than we commonly think

#21

Post by JPLeRouzic »

jlawson wrote: post #19
themgt wrote: post #3

While this article's content isn't exactly wrong, the Wikipedia on "Identical ancestors point" gives some important context for what's actually being asserted: All living people share exactly the same set of ancestors from this point back, all the way to the very first single-celled organism. However, people will vary widely in how much ancestry and genes they inherit from each ancestor, which will cause them to have…

Another important point here is that genes don't divide infinitely, so that if you go back some distance, you start finding ancestors from whom you actually didn't get any DNA. The book Who We Are and How We Got Here talks about this. When DNA recombines at conception, it only snips and stitches in a fairly limited number of places. It doesn't 'mix' finely like paint. It's more like taking two short pamphlets of ~25…

>> The genetic evolutionary difference between distinct groups like Europeans, sub-Saharan Africans, ... is something like 70,000 years of divergent evolution with very very minimal gene flow between the groups.

Any citation?

Re: Humans are more closely related than we commonly think

#23

Post by shuringai »

Problem is, The article assume humans mate with uniform distribution, and that they did so generations ago. The 2^n argument is way naive and this level of uniformity assumes every people on earth has the chance to end up with a uniform random other person as their partner, regardless of geographic, cultural etc differences.

Re: Humans are more closely related than we commonly think

#24

Post by jerzyt »

Disclaimer - the last thing I want to do is to start a religious debate on HN. So, please, don't down-vote me because I'm going to mention Bible here. But I find it interesting that the Individual Ancestors Point is not that far off from the Biblical estimate of the Earth's age of about 6,000 to 15,000 years. So forget about "planting" the planet with "fake" fossils, Adam and Eve are right on the same timeline as the IAP. Which really isn't that surprising because that basically indicates the age of a modern human being, capable of passing down stories through an invention of a language, and eventually writing them down. So, at least in this case, the Bible got the math down fairly well, and I'm bringing it up purely as a historical document here.

Re: Humans are more closely related than we commonly think

#25

Post by TeMPOraL »

titzer wrote: post #4
themgt wrote: post #3

While this article's content isn't exactly wrong, the Wikipedia on "Identical ancestors point" gives some important context for what's actually being asserted: All living people share exactly the same set of ancestors from this point back, all the way to the very first single-celled organism. However, people will vary widely in how much ancestry and genes they inherit from each ancestor, which will cause them to have…

An intuition about the "appearing trillions of times in a family tree" is to realize that family trees are actually a binary tree extending backwards in time --i.e. each person has exactly two parents, who have exactly two parents, and so on. So N generations back, there are 2^N individuals. Obviously, there weren't 2^100 people on Earth at any point in time, so this backwards tree starts folding back on itself, cont…

To play with the river analogy: and then imagine that it flows next to a dye factory, and every now and then a droplet of dye finds its way to the stream, creating a colorful streak. That's to account for random mutations.

And then what would an analogy look for prokaryotes - bacteria, archaea? If my understanding of biology is correct, it would be like an infinitely tall, densely tiered waterfall. There's some forward generational movement, but there's also plenty of lateral ones - exchanging gene packets "at runtime".

Re: Humans are more closely related than we commonly think

#26

Post by jerzyt »

JPLeRouzic wrote: post #5
themgt wrote: post #3

While this article's content isn't exactly wrong, the Wikipedia on "Identical ancestors point" gives some important context for what's actually being asserted: All living people share exactly the same set of ancestors from this point back, all the way to the very first single-celled organism. However, people will vary widely in how much ancestry and genes they inherit from each ancestor, which will cause them to have…

The point in the article is that at many generations ago, we are heavily inbred, it is not that we are all related. If you look at one generation ago one have 2 * 2 ^ 0 ancestors, at two generations, one have 2 * 2 ^ 1 ancestors, etc. At 27 generations one apparently has more ancestors than people in the world at that time. This apparent paradox stems from the fact that we are heavily inbred. Thus the article is corr…

> The point in the article is that at many generations ago, we are heavily inbred, it is not that we are all related.

I'm not following your point - maybe it's just a linguistic thing. To me, inbreeding implies relation, at least blood-relation, even when there was no other relation, e.g. conquering armies raping and pillaging.

No argument with your math.

Re: Humans are more closely related than we commonly think

#27

Post by irrational »

themgt wrote: post #3

While this article's content isn't exactly wrong, the Wikipedia on "Identical ancestors point" gives some important context for what's actually being asserted: All living people share exactly the same set of ancestors from this point back, all the way to the very first single-celled organism. However, people will vary widely in how much ancestry and genes they inherit from each ancestor, which will cause them to have…

Aren’t you just reiterating the entire second half of the article?

Re: Humans are more closely related than we commonly think

#28

Post by jsnk »

titzer wrote: post #16
samatman wrote: post #6

So I was wondering if this article was just being incredibly misleading or straightforwardly lying, and I hit this: > “If you were alive at the genetic isopoint, then you are the ancestor of either everyone alive today or no one alive today,” Yeah. That's a lie. There's no way around it, this is a dishonest statement. I'm in no kind of mood to explain why that is, for pretty predictable reasons this conversation goes…

Your intuition on this is wrong, and there's no need to fly off the handle. Ancestry is infectious. Take two populations, A and B, completely isolated from each other. (nevermind that they all have a common ancestor long before the populations diverged). Now one day in 1000 B.C. a single individual from population A migrates over to population B, mates, and has offspring (more than 1) with an individual from populati…

"The key is that the propagation of ancestry never stops, because ancestry doesn't round down to zero."

I get your other points but this assumption seems obviously wrong. Plenty of people historically did not live to leave children behind. Then of course, we can have complete stops in the propagation of ancestry.

Re: Humans are more closely related than we commonly think

#29

Post by ahartmetz »

jlawson wrote: post #19
themgt wrote: post #3

While this article's content isn't exactly wrong, the Wikipedia on "Identical ancestors point" gives some important context for what's actually being asserted: All living people share exactly the same set of ancestors from this point back, all the way to the very first single-celled organism. However, people will vary widely in how much ancestry and genes they inherit from each ancestor, which will cause them to have…

Another important point here is that genes don't divide infinitely, so that if you go back some distance, you start finding ancestors from whom you actually didn't get any DNA. The book Who We Are and How We Got Here talks about this. When DNA recombines at conception, it only snips and stitches in a fairly limited number of places. It doesn't 'mix' finely like paint. It's more like taking two short pamphlets of ~25…

I agree with you about the "noble" lies. You wrote something else that I have never seen before and that seems quite interesting:

> When DNA recombines at conception, it only snips and stitches in a fairly limited number of places. It doesn't 'mix' finely like paint.

I had always assumed that clearly recognizable traits that children inherit from parents are simply based on the large influence of certain small pieces of DNA. Do you know a good text that discusses that?

Re: Humans are more closely related than we commonly think

#30

Post by titzer »

TeMPOraL wrote: post #25
titzer wrote: post #4

Earlier quoted context omitted.

An intuition about the "appearing trillions of times in a family tree" is to realize that family trees are actually a binary tree extending backwards in time --i.e. each person has exactly two parents, who have exactly two parents, and so on. So N generations back, there are 2^N individuals. Obviously, there weren't 2^100 people on Earth at any point in time, so this backwards tree starts folding back on itself, cont…

To play with the river analogy: and then imagine that it flows next to a dye factory, and every now and then a droplet of dye finds its way to the stream, creating a colorful streak. That's to account for random mutations. And then what would an analogy look for prokaryotes - bacteria, archaea? If my understanding of biology is correct, it would be like an infinitely tall, densely tiered waterfall. There's some forwa…

To be clear, the river can divide, too. That's speciation, where populations no longer interbreed because their offspring are either unviable or themselves cannot produce offspring.
Post reply on HN