The end of the Neanderthals

[Beebo Brink]

So many theories to choose from to explain the disappearance of Neanderthals. Here's a solid one that would explain that extinction event on its own, much less in concert with other theories.

Inbreeding, Allee effects and stochasticity might be sufficient to account for Neanderthal extinction

The replacement of Neanderthals by Anatomically Modern Humans has typically been attributed to environmental pressure or a superiority of modern humans with respect to competition for resources. Here we present two independent models that suggest that no such heatedly debated factors might be...

journals.plos.org

Our results indicate that the disappearance of Neanderthals might have resided in the smallness of their population(s) alone: even if they had been identical to modern humans in their cognitive, social and cultural traits, and even in the absence of inter-specific competition, Neanderthals faced a considerable risk of extinction. Furthermore, we suggest that if modern humans contributed to the demise of Neanderthals, that contribution might have had nothing to do with resource competition, but rather with how the incoming populations geographically restructured the resident populations, in a way that reinforced Allee effects, and the effects of inbreeding and stochasticity.

Summarized, sheer population numbers for Neanderthals were small, and spread among such distant geographic regions that the individual breeding groups were far smaller still. This led to inevitable inbreeding that lowered viability. And lastly, the impact in variations of mate-availability, deaths and births is much higher in a small population. Eventually, you roll snake-eyes on no mates, high deaths and low births.

Not discussed in the article is that this might also explain why we have Neanderthal genes in our species. There simply weren't enough of their own kind to afford to be picky about who you slept with. Earlier this year there were several articles about an archeological find of a young girl who was mixed Neanderthal and Denisovan. Perhaps it was a paleolithic Romeo & Juliet story, or maybe it was making do with what you've got.

 

[danielravennest]

So many theories to choose from to explain the disappearance of Neanderthals. Here's a solid one that would explain that extinction event on its own, much less in concert with other theories.

Not discussed in the article is that this might also explain why we have Neanderthal genes in our species. There simply weren't enough of their own kind to afford to be picky about who you slept with. Earlier this year there were several articles about an archeological find of a young girl who was mixed Neanderthal and Denisovan. Perhaps it was a paleolithic Romeo & Juliet story, or maybe it was making do with what you've got.

There's no Neanderthal Y chromosome genes in modern humans, indicating that our ancestors thought Neander chicks were hot. Alternately, the larger cross-breed babies weren't viable in human mothers. Given that Neander genes are 1.5-2% of non-African populations, there's a lot more of their genes around now than when they were a separate population (thousands to tens of thousands population).

 

[Beebo Brink]

There's no Neanderthal Y chromosome genes in modern humans, indicating that our ancestors thought Neander chicks were hot.

My first extremely cynical reaction is that apparently Neanderthal men didn't rape women, but the same can't be said for modern human males.

 

[Kara Spengler]

There's no Neanderthal Y chromosome genes in modern humans, indicating that our ancestors thought Neander chicks were hot.

When was beer discovered again?

 

[Myficals]

My first extremely cynical reaction is that apparently Neanderthal men didn't rape women, but the same can't be said for modern human males.

At the risk of getting into some weird and uncomfortable conversations about at what exact point the term rape becomes meaningful, nature in general is pretty rapey. Forced sex happens all the time. There's lots of examples of species wherein the females have developed strategies for dealing with sperm from undesirable mates, and the males have strategies for tricking and/or forcing sex on unwitting mates.

What I'm saying is, I doubt the rapes weren't happening in both directions. If I were to hazard a guess, I suspect it's more something to do with Homo sapiens women being unable to carry neanderthal crosses to term.

 

[Pamela]

I have some Neanderthal dna. But what I don’t understand, is how two species can produce viable progeny. I thought that, for example, horses and donkeys could produce mules, but mules cant procreate.

i never ever see this explained. Until I do I am just going to assume that Neanderthals were not a separate species from humans.

 

[Myficals]

I have some Neanderthal dna. But what I don’t understand, is how two species can produce viable progeny. I thought that, for example, horses and donkeys could produce mules, but mules cant procreate.

i never ever see this explained. Until I do I am just going to assume that Neanderthals were not a separate species from humans.

"Species" is kind of a slippery delineation, there are all sorts of questions that can arise when trying to classify organisms and the answers are rarely cut and dried. I suggest googling (the) "species problem" if you want some decent insights into how much of a mess it really is.

Just on Neanderthals however, it's not even universally accepted that they are a separate species to modern humans. Some models classify them as a subspecies, Homo sapiens neanderthal and us as Homo sapiens sapiens.

 

[Beebo Brink]

I have some Neanderthal dna. But what I don’t understand, is how two species can produce viable progeny. I thought that, for example, horses and donkeys could produce mules, but mules cant procreate.

"Species" is kind of a slippery delineation, there are all sorts of questions that can arise when trying to classify organisms and the answers are rarely cut and dried.

The entire structure of the taxonomy of life is more of an organizing concept than a scientific "fact." There is constant shuffling and re-shuffling of organisms from one place to another and there are frequent scientific flame wars over where to draw the line for species or whether that term is even useful. Some species are separated by geography or differing mating patterns and could theoretically interbreed, but practically speaking they don't (many bird species). Others species are obviously closely related -- lions and tigers both have 38 chromosomes -- but have sufficient differences in those chromosomes that when they interbreed their offspring are sterile.

Many canine species display obvious differences, but the wolf, dingo, dog, coyote, and golden jackal all have 78 chromosomes arranged in 39 pairs. Not surprisingly, at least some of them can interbreed with fertile offspring such as the wolf-dog hybrid and coydogs. In contrast, humans and chimp are not quite as close, with 23 pairs of chromosomes for us but 24 for them. That's uncomfortably close to being able to mate and produce sterile offspring. There's no reputable account (that I've heard) of that happening. One can only pray it hasn't.

But it's believed that Neanderthals and Denisovans had 23 chromosomes, so there's no reason we couldn't interbreed just as wolves and dogs can interbreed.

 

[Essence Lumin]

Then there are alpacas and llamas.

 

[Beebo Brink]

This is a bit off tangent, but during the 70s and 80s, Oliver the Chimpanzee was promoted as a human-chimp hybrid with 47 chromosome pairs. Eventually DNA analysis proved him to have the standard 48 of a pure chimpanzee. I remember seeing one especially startling photo of him, that really did make you wonder if that kind of unholy mix was possible. The story is still out there on the fringes, never dying.

 

[Aribeth Zelin]

I'm a fair bit Neanderthal, but then, most all of my DNA from the last 500 years is Europe [Polish, German, Slavic primary], so that makes sense.

And I'd love if they would start showing the amount of some of the other extinct subspecies of humanity that are supposed to still have dna found in us.

 

[Free]

Then there are alpacas and llamas.

I like to call them Lolpacas.

 

[danielravennest]

When was beer discovered again?

Just after grains were domesticated, but that was long after purebred Neanders were gone.

(Yes, I know you were making a joke)

 

[danielravennest]

This is a bit off tangent, but during the 70s and 80s, Oliver the Chimpanzee was promoted as a human-chimp hybrid with 47 chromosome pairs.

I'll have to check to be sure, but there seems to be a missing link in your post.

 

[danielravennest]

I'm a fair bit Neanderthal, but then, most all of my DNA from the last 500 years is Europe [Polish, German, Slavic primary], so that makes sense.

And I'd love if they would start showing the amount of some of the other extinct subspecies of humanity that are supposed to still have dna found in us.

Denisovans are the only other group to have confirmed presence in human DNA. They are named after a cave in Siberia , whose average temperature is right at freezing, which helped preserve the DNA.

 

[Katheryne Helendale]

I'll have to check to be sure, but there seems to be a missing link in your post.

 

[Dakota Tebaldi]

What I'm saying is, I doubt the rapes weren't happening in both directions. If I were to hazard a guess, I suspect it's more something to do with Homo sapiens women being unable to carry neanderthal crosses to term.

I suppose it's always possible too that male neanderthal crosses were sterile. Or never allowed to reach maturity.

 

[Ashiri]

I don't think too much can be read into the non-existence of Neanderthal Y chromosome genes in the modern human genome when the total amount of genes from them is in the single digits of percent and when the Y chromosome is so small.

 

[Fionalein]

I have some Neanderthal dna. But what I don’t understand, is how two species can produce viable progeny. I thought that, for example, horses and donkeys could produce mules, but mules cant procreate.

i never ever see this explained. Until I do I am just going to assume that Neanderthals were not a separate species from humans.

Species are considered seperate when there are interbreeding boundaries. Those can be genetical incompatibility but also spatial seperation - hell also temporal seperation. There are two types of ibex which are considered different species because they don't interbreed as their breeding seasons don't overlap. Spatial boundaries can fall, take American sycamore and Oriental plane - those trees were on different continents - no way would they interbreed - ergo different species ... until we started planting them next to each other in parks and tree lined roads that is...

Speciation, the process of seperate species emerging from common ancestors is pretty weird and rather complex especially if you look at plants (hurray for polyploid hybrid species complexes). It does not help the definition of what makes a species is not set in stone (biologists don't have the luxury of fundamental abstract rules as in mathematics - nature just does not care much about such simple models)

Also it is not as easy as that. Mules usually are infertile - I don't know the percentage (must be less than 1) but that is not 100% true, some mules are fertile.

Also take a look at cats, There are the popular breeds Bengal, Chaussie and Savannah,... all fertile breeds originating from 2 species hybrids, and well, ... Savannahs sometimes even have 3 species as ancestors as sometimes the servals are crossbred with bengals (which are already a hybrid breed of cat).

 

[Aribeth Zelin]

So, since mules have come up. There is someone who's field is intraspecies crosses, like horse/donkey, lion/tiger, and so forth. He posits the reason human litters are so tiny [from a mammal pov], as well as our range of pigment, relative hairlessness, and other factors, is because we're a mule species.

Except we're part proto-bonobo and part boar.

A machine that can analyze flavours, when texted by humans, suggests we would taste like pork, and well, the whole long big thing too.

Anyway, I always thought that was an interesting theory.