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As a non-biologist, am I the only one who had a claim like this raise my eyebrow in skepticism? What does it mean to be a separate species if you're interbreed

As a non-biologist, am I the only one who had a claim like this raise my eyebrow in skepticism? What does it mean to be a separate species if you're interbreeding in a significant way? What does it mean to have n٪ Neanderthal DNA if that DNA is found in a significant proportion of "modern humans"?

i386 7y ago
There are many species that are separated by 100K/1M years that are still able to interbreed. Horses, Donkeys, Zebras are a good example. These animals can produce viable offspring but still have significant anatomical differences (those differences tend to define what we call species)
- ACow_Adonis 7y ago
  Yes, but they are notable because of their exceptional nature, and where many of them do interbreed, the understanding is they often/ predominantly produce sterile offspring, and thus do not/ have not spread in any meaningful way through the resulting population. If 'Neanderthal DNA' is found in a huge percentage of 'modern humans', on the face of if, it seems to me the notion that Neanderthals should be considered a separate species is the preposition that seems somewhat/increasingly spurious...
  - danieltillett 7y ago
    Could you explain why you think the number of hybrid offspring of Neanderthals currently living prevents Neanderthals being a different species? This is like saying that if there are a large number of mules alive that donkey’s can’t be considered a different species to horses. There is evidence that the offspring of the Neanderthal hybrids follow Haldane's Rule [1]. 1. https://en.wikipedia.org/wiki/Haldane%27s_rule https://en.wikipedia.org/wiki/Haldane%27s_rule
toasterlovin 7y ago
> What does it mean to be a separate species if you're interbreeding in a significant way? Species is a squishy concept. You might be amazed at how much intense arguing that continues to be about what delineates two closely related species. I think it's hard to consider Neanderthals a separate species, given what we now know thanks to ancient DNA. I think the term sub-species makes more sense. > What does it mean to have n٪ Neanderthal DNA if that DNA is found in a significant proportion of "modern humans"? It means that before the point at which the lineage that we call "humans" interbreed with the lineage that we call "neanderthal", these particular pieces of DNA were found only in the neanderthal lineage.
- ACow_Adonis 7y ago
  And is that actually the case in the instance of modern humans and the distribution of genetic components? (Genuinely asking for someone more knowledgeable to chime in here). I admit my sort of base assumption is that simple quantitative metrics such as n% African/n% Neanderthal peddled by the likes of online genetics testing labs are grossly oversimplified at best and probably borderline meaningless at worst...
  - toasterlovin 7y ago
    Sorry, I’m not sure what you’re asking. Can you restate? Regarding ancestry testing: it’s pretty valid, in general. DNA extracted from ancient human remains has completely revolutionized our understanding of recent, ancient, and extremely ancient human history. The online testing companies use the same methods and data sets. The way they present results boils a lot of different stuff down to a single number, so nuance and some fidelity is inevitably lost, but that’s always an issue when you try and make a nuanced subject understandable to laypeople. But, generally speaking, if an online test says that your DNA is 5% Neanderthal whereas someone else’s is 1%, or that you’re 20% Western European and 40% Eastern European, that is probably a valid way to present things.
droithomme 7y ago
> What does it mean to be a separate species if you're interbreeding in a significant way? Yes, great question. Pheasants and chickens can breed and produce fertile offspring, along with many other combinations. Are they different species? Most say they are, but why given matching chromosomes? They look dramatically different and are from different areas, true, but just like Native American Chihuahuas and Greek Harehounds, both which we claim to be dogs. They definitely don't look the same to me, or to most people. As far as Homo Sapiens Neanderthals goes, well... yes, some still say that's actually Homo Neanderthals, but a lot now agree it's not really a different species. Source of quite a few bitter fights in academia though.
danieltillett 7y ago
This gets into a really complex topic about what is a species. Everyone considers lions and tigers separate species yet put them together they will interbreed creating a liger [0]. Ligers are even fertile. As for what it means if some of us have Neanderthal DNA and some don’t is some of us are a hybrid species [1]. 0. https://en.wikipedia.org/wiki/Liger https://en.wikipedia.org/wiki/Liger 1. https://en.wikipedia.org/wiki/Hybrid_(biology) https://en.wikipedia.org/wiki/Hybrid_(biology)

i386 7y ago

There are many species that are separated by 100K/1M years that are still able to interbreed. Horses, Donkeys, Zebras are a good example. These animals can produce viable offspring but still have significant anatomical differences (those differences tend to define what we call species)

ACow_Adonis 7y ago
Yes, but they are notable because of their exceptional nature, and where many of them do interbreed, the understanding is they often/ predominantly produce sterile offspring, and thus do not/ have not spread in any meaningful way through the resulting population. If 'Neanderthal DNA' is found in a huge percentage of 'modern humans', on the face of if, it seems to me the notion that Neanderthals should be considered a separate species is the preposition that seems somewhat/increasingly spurious...
- danieltillett 7y ago
  Could you explain why you think the number of hybrid offspring of Neanderthals currently living prevents Neanderthals being a different species? This is like saying that if there are a large number of mules alive that donkey’s can’t be considered a different species to horses. There is evidence that the offspring of the Neanderthal hybrids follow Haldane's Rule [1]. 1. https://en.wikipedia.org/wiki/Haldane%27s_rule https://en.wikipedia.org/wiki/Haldane%27s_rule

toasterlovin 7y ago

> What does it mean to be a separate species if you're interbreeding in a significant way? Species is a squishy concept. You might be amazed at how much intense arguing that continues to be about what delineates two closely related species. I think it's hard to consider Neanderthals a separate species, given what we now know thanks to ancient DNA. I think the term sub-species makes more sense. > What does it mean to have n٪ Neanderthal DNA if that DNA is found in a significant proportion of "modern humans"? It means that before the point at which the lineage that we call "humans" interbreed with the lineage that we call "neanderthal", these particular pieces of DNA were found only in the neanderthal lineage.

ACow_Adonis 7y ago
And is that actually the case in the instance of modern humans and the distribution of genetic components? (Genuinely asking for someone more knowledgeable to chime in here). I admit my sort of base assumption is that simple quantitative metrics such as n% African/n% Neanderthal peddled by the likes of online genetics testing labs are grossly oversimplified at best and probably borderline meaningless at worst...
- toasterlovin 7y ago
  Sorry, I’m not sure what you’re asking. Can you restate? Regarding ancestry testing: it’s pretty valid, in general. DNA extracted from ancient human remains has completely revolutionized our understanding of recent, ancient, and extremely ancient human history. The online testing companies use the same methods and data sets. The way they present results boils a lot of different stuff down to a single number, so nuance and some fidelity is inevitably lost, but that’s always an issue when you try and make a nuanced subject understandable to laypeople. But, generally speaking, if an online test says that your DNA is 5% Neanderthal whereas someone else’s is 1%, or that you’re 20% Western European and 40% Eastern European, that is probably a valid way to present things.

droithomme 7y ago

> What does it mean to be a separate species if you're interbreeding in a significant way? Yes, great question. Pheasants and chickens can breed and produce fertile offspring, along with many other combinations. Are they different species? Most say they are, but why given matching chromosomes? They look dramatically different and are from different areas, true, but just like Native American Chihuahuas and Greek Harehounds, both which we claim to be dogs. They definitely don't look the same to me, or to most people. As far as Homo Sapiens Neanderthals goes, well... yes, some still say that's actually Homo Neanderthals, but a lot now agree it's not really a different species. Source of quite a few bitter fights in academia though.

danieltillett 7y ago

This gets into a really complex topic about what is a species. Everyone considers lions and tigers separate species yet put them together they will interbreed creating a liger [0]. Ligers are even fertile. As for what it means if some of us have Neanderthal DNA and some don’t is some of us are a hybrid species [1]. 0. https://en.wikipedia.org/wiki/Liger https://en.wikipedia.org/wiki/Liger 1. https://en.wikipedia.org/wiki/Hybrid_(biology) https://en.wikipedia.org/wiki/Hybrid_(biology)