Question about 1-4% Neanderthal DNA present in non African humans

[DuaneW]

Hello!

I have a two part question that hopefully someone can shed some light on:

1) Is it true that humans of non African descent share a small percentage of DNA with Neanderthals?

2) If (1) above is true, then are we and Neanderthals the same species?

My understanding of _species_ is a population of individuals who can produce fertile offspring. Hence, while a donkey stallion and a horse mare can produce an offspring called a mule, the mule itself is sterile because horses and donkeys are different species, so it can't pass its genes on to the next generation.

My gut feeling is that (2) may still be an open question. Or perhaps I should have paid more attention in biology class.

[Shaula]

It might be more accurate to define us as sub-species, Neanderthals are alternatively classed as Homo sapiens neanderthalensis. In a similar manner to this there are also genes from the Denisova line in some areas of the world.

[HenrikOlsen]

My understanding of _species_ is a population of individuals who can produce fertile offspring. Hence, while a donkey stallion and a horse mare can produce an offspring called a mule, the mule itself is sterile because horses and donkeys are different species, so it can't pass its genes on to the next generation.

My gut feeling is that (2) may still be an open question. Or perhaps I should have paid more attention in biology class.

Speciation is a grayscale, not black and white. There are examples of everything from "produces fertile offspring" over "the relevant bits don't fit" to "nothing happens",

My impression is that biologists consider populations to be different species when they don't breed, not when they can't.
And 1-4% seems to be an awfully low number given the 90+% we have in common with a gorilla. (and the 50% we have in common with a banana)

[ShinAce]

Speaking of gorrilas, I found it interesting that we share say, 95% of our DNA with gorillas and 95% with chimpanzees. The genes tend to say we come from chimps, but we share genes with gorillas that chimps do not. At first glance, you might say we are the chimp's cousin, but the speciation between the three of us is peculiar.

The 1-4% is to say that non-African humans have 1-4% MORE in common with Neanderthal than do subsaharan Africans.

[swampyankee]

Somewhere or another there's a cladistic diagram showing the relationship between humans and the other great apes. (here's one!). Currently, the consensus is that humans are most closely related to chimpanzees & bonobos.

The genetic difference between humans and Neanderthals is about half the difference between humans and chimps (see http://humanorigins.si.edu/evidence/...d-neanderthals).

[Shaula]

I think you need to interpret those figures differently to how they are presented. We share about 50% of our DNA with everything from fish to insects. And bananas. I suspect they mean something like that within the variations we see in human population 1-4% of that DNA comes from a Neaderthal pool.

[pzkpfw]

We even have some virus DNA in us, does that make influenza our cousin?

[swampyankee]

We even have some virus DNA in us, does that make influenza our cousin?

Only very distantly: trillionth cousin, one billion times removed.

[Tobin Dax]

Speaking of gorrilas, I found it interesting that we share say, 95% of our DNA with gorillas and 95% with chimpanzees. The genes tend to say we come from chimps, but we share genes with gorillas that chimps do not. At first glance, you might say we are the chimp's cousin, but the speciation between the three of us is peculiar.

Apparently it's really not peculiar, nor is it unexpected. PZ Myers has a short explanation of this on Pharyngula. (skip the two block quotes at the beginning if you don't want to read him tear into people.)

[Cougar]

I think you need to interpret those figures differently to how they are presented. We share about 50% of our DNA with everything from fish to insects. And bananas. I suspect they mean something like that within the variations we see in human population 1-4% of that DNA comes from a Neaderthal pool.

Further clarification is found in ShinAce's link:

Most human sequences differ from each other by on average 8.0 substitutions, while the human and chimpanzee sequences differ by about 55.0 substitutions. The Neanderthal and modern human sequences differed by approximately 27.2 substitutions.

[Ara Pacis]

How much of the Neanderthal genes were on the Y-chromosome? I'm curious if the genetic exchanges were both ways or mostly one way. Instead of Mars and Venus perhaps it should be Men are from Europe, Women are from Africa.

[syzygy42]

For popular explanations and in depth analysis on everything Neanderthal, John Hawks is my go-to guy.

[whimsyfree]

How much of the Neanderthal genes were on the Y-chromosome?

AFAIK, zero. Also nil mitochondrial.

I'm curious if the genetic exchanges were both ways or mostly one way.

I'm not sure what you mean by "way" in this context but the genetic findings are consistent with Neanderthal males mating with human females. Haldane's rule explains the apparent lack of Neanderthal Y chromosomes in the modern population.

Instead of Mars and Venus perhaps it should be Men are from Europe, Women are from Africa.

That doesn't make sense.

[swampyankee]

Whimsyfree: it's a book reference.

[whimsyfree]

Whimsyfree: it's a book reference.

I realize that but it still doesn't make sense. The (possible) fact that there's a male Neanderthal a 1000 generations back in my family tree doesn't somehow make me more Neanderthal than it does my sister.

I take this Neanderthal ancestry hypothesis with a grain of salt. As recently as 2003 a study published in Science concluded that "Modern humans replaced the Neanderthals with little or no gene exchange".

[Ara Pacis]

That doesn't make sense.

Humans came out of Africa, no? Neanderthals tended to be in Europe, no?

For one who has "whimsy" in their name...

[novaderrik]

Humans came out of Africa, no? Neanderthals tended to be in Europe, no?

For one who has "whimsy" in their name...

to be fair, they have the word "free" attached to the end of the word "whimsy", which makes a word that means "without whimsy"..

[HenrikOlsen]

Actually the name specifically declares a lack of whimsy.

Incidentally, the Pharyngula explanation of the gene difference missed one likely cause for the "gene in common with Gorillas but not with Chimps" thing.

When humans split from chimps, that was because several genes where changed in both branches, it's entirely possible that several of those genes that changed chimps from the chimp-human common ancestor were not changed in humans and were identical to those inherited from the common human-chimp-gorilla ancestor.

[whimsyfree]

Actually the name specifically declares a lack of whimsy.

Feet firmly planted half a metre below the ground, that's me.

Incidentally, the Pharyngula explanation of the gene difference missed one likely cause for the "gene in common with Gorillas but not with Chimps" thing.

When humans split from chimps, that was because several genes where changed in both branches, it's entirely possible that several of those genes that changed chimps from the chimp-human common ancestor were not changed in humans and were identical to those inherited from the common human-chimp-gorilla ancestor.

Yairs. There is a tendency to assume that the changes all took place in the "more advanced" human line.

[NEOWatcher]

My impression is that biologists consider populations to be different species when they don't breed, not when they can't.

I'm not sure how those two ("don't"/"can't") are distinguished.
For some reason it left me with the various forms of a "farmer and a sheep..." joke coming to mind.

[Shaula]

"Don't" usually refers to creatures which have behaviourally speciated. A good example would be periodic cicadas - they have very long underground phases and very short sexually active phases (and have prime number cycles). So they can speciate quite easily like this - which may be why there are several species of 17 year ones which have 13 year counterparts. They are counted as different species but can only be told apart by their lifecycle differences.

[SkepticJ]

Are racists a different species because they refuse to take a healthy canon ball splash into the gene pool? Or does it only count if its ingrained as an instinct, not learned behavior?

[Shaula]

I make it a personal rule never to discuss speciation with respect to humans. Far too emotive a subject, and too full of pitfalls.

Edit: I meant to say modern human populations - obviously I have been talking about neanderthals and other human species in the past!

[DuaneW]

Thanks everyone. Definitely food for thought, and thanks for the John Hawks blog. Bookmarked.

I like the idea that Humans and Neanderthals are separate subspecies, but I'm open to the truth, whatever it may turn out to be.

[HenrikOlsen]

I'm not sure how those two ("don't"/"can't") are distinguished.
For some reason it left me with the various forms of a "farmer and a sheep..." joke coming to mind.

If artificial insemination works but they don't mate in mature, then it's "don't" rather than "can't".

[NEOWatcher]

If artificial insemination works but they don't mate in mature, then it's "don't" rather than "can't".

That makes sense.
I probably shouldn't ask because of my sheep example, but I'm sure there's a specific definition of "mate".

[John Mendenhall]

My partner and I work an outdoor flea market on the weekends. A number of our customers have prominent brow and cranial ridges, strong heavy builds, wear animal skins, and have trouble vocalizing. 98% cases?

Seriously, I suspect the shared genes predate the species split.

[DoggerDan]

Article. Source: Fifth Annual World Science Festival, Saturday, June 2, 2012, New York, NY.

Notable Excerpts:

"Braininess helped us broaden our diets"

"Modern humans had technology that allowed them to get a more consistent, reliable and balanced diet..."

"Another handy cognitive capacity allowed the rapid spread of new technologies, as well as the sharing of knowledge and information relevant for survival: We were — and clearly still are — adept social networkers."

So, were they separate species, or were they interbred?

"DNA analysis shows the humans interbred with these strangers" (descendants of hominin groups that had left Africa during prior waves of migration)

[Ara Pacis]

"Another handy cognitive capacity allowed the rapid spread of new technologies, as well as the sharing of knowledge and information relevant for survival: We were — and clearly still are — adept social networkers."

I always suspected that religion played a large role

[swampyankee]

Are racists a different species because they refuse to take a healthy canon ball splash into the gene pool? Or does it only count if its ingrained as an instinct, not learned behavior?

Alas, no, although racial differences in multi-ethnic communities, like the US, are maintained by culturally-mediated behavior. I think most biologists would consider the behavior separating species as something instinctive vs cultural.

I think one of the most interesting features of speciation are ring species, where there is a chain of interbreeding populations between two species which cannot or do not interbreed despite geographic proximity. Larus gulls form an interesting population.... Another interesting group is the periodic cicadas. Assuming there is no crossover between broods (there may be, although some broods are locally extinct), there will be genetic differences between the broods, which could give some clues as to the origin of this reproductive pattern. Is it possible that, at some future time, the different broods will show sufficient genetic difference to qualify as distinctive species?