Just how different two organisms have to be to be different species is always going to be arbitrary. It is not as though you can select a particular day (the absurd extreme) two populations transitioned from one species to two. Given this (and more reasonable arguments in the same vein over longer time periods), a particular number of “species” in a closely related group over an evolutionary short timeframe just isn’t an interesting or useful metric.
What I wonder is how climate/geography pushed advanced (by that I mean enough brain power and memory to recognize siblings and belong to an group) species to evolve to the point that they didn't consider each others as parents.
Well, if AxB and BxC can mate, then the off spring has genes from A and C so by some second degree derivative they can mate. iff.
Not my field of interest but I feel reminded of dialects and how difficult it is to define language. The dialect with a military meme has some truth to it, when variet are measured against a standard or prestige dialect. B obviously has an advantage so unless other disadvantages apply, it would be dominant.
A societal (?) or socio-cultural definition is interesting as well. Even genetically identical specimen couldn't mate if on opposite sites of the globe, and they are bound to drift eventually. I do kindle with the idea that groups have to be understood as organisms in their own right, but I never read anything specific about it.
About language families, it is startling how anthropologists reason about language by proxy via archaogenetics. Lots of open questions there, too.
This is likewise something which doesn’t just turn off one day. Lots of very distinct animals have some degree of interbreeding possible more than one would think. Plants are very much more willing to mix species, and many organisms don’t do sex at all and bacteria types do a whole lot of gene transfer...
You aren’t going to get a half deer half turtle, but the closer two organisms are, the more likely they have some degree of compatibility, even after millions of years of evolution.
It’s like asking people to determine if a color is orange or red. There are obvious answers and not so obvious answers.
This has so many edge cases that it's really more of a vague rule of thumb than a hard definition: ring species (as another poster pointed out), infertile individuals (does every infertile individual constitute a species by itself?), drift over time (like ring species, but over time: an individual might be able to (in theory) produce fertile offspring with a far ancestor or with a far descendant, but the far ancestor may not be able to mate with the far descendant), ...
I learned that obsolete definition too (I'm old!) but the article touches on the problems that caused that definition to fall into abeyance (e.g. species that reproduce asexually)
I don't think this makes sense. If Neanderthals are the same species then there wasn't any mixing, it was just regular procreation. If there was mixing then Neanderthals necessarily were other species.
I didn't claim they were a different species. There were more likely a long isolated subspecies still genetically capable of reproducing with cromagnons, which is evident by the presence of their genes in modern humans.
And they aren't the only examples of that, either (i.e consider Denisovans)
I thought species were defined as being broadly unable to interbreed? (Yes, mules and ligers exist but they’re exceptions to the rule produced by human intervention.)
wolf and dogs's offsprings can interbreed just fine, and have even more mixed offsprings, but they are considered different species
"Wolves (canis lupus), coyotes (canis latrans), and domestic dogs (canis familiaris) are closely-related species. All three can interbreed and produce viable, fertile offspring — wolfdogs, coywolves, and coydogs. Through DNA analysis, scientists have established that the wolf is the ancestor of the dog."
Yes, but Homo Sapiens interbred with Neanderthals and probably also Denisovans [1]. Different species, yes, but still able to interbreed to an extent. Where exactly the line between species lies is not so clear, even though it clearly exists, just like the line between red and orange.
Is there evidence for that mating could only occurr "to an extent," like with horses and donkeys? Is there a physiological difference making it difficult for, say, difficulties in mating between Homo sapiens and Neanderthals, or between Homo sapiens and Denisovans?
There can be a number of reasons for the two not mating often outside mere physiological differences, for instance differences in preferred culture, looks and personality. While some of that can certainly be the result of biological differences, it's not necessarily so. I'm just guessing and theorizing here, though, so any leads, links or breadcrumbs would be nice. :)
This quote is from way down in the article but I think the most significant one:
> Most intriguingly, something of the dynamics is visible. In some earlier instances, Neanderthal women had the children of H sapiens men, but the later interbreeding after 60,000 years ago tells a different story. Nobody today has mitochondrial DNA like that in Neanderthals and, since it’s passed only maternally, this implies that interbreeding was more often between their men and our women.
Some other interesting ones:
> unlike other primates, Neanderthal body size doesn’t seem to have differed much between the sexes. It’s much more similar to most H sapiens populations, which suggests that violent male competition was not the dominant social structure. Instead, more likely something akin to the bonobos, whose adult lives are based around long-term female friendships, might have been possible.
> Somewhere around 40,000 years ago, the many generations of Neanderthal women become invisible, at least in skeletal terms. The processes underlying this must have come in many guises, in many places, but one thing we know is that women of another kind – H sapiens – played some part, because Neanderthals were not entirely extinguished. Just 10 years ago, the first nuclear genome was meticulously reconstructed from three genetically identified females at Vindija; it revealed that, rather than ousting Neanderthals from Eurasia, we had in fact interbred with them.
> Is there evidence for that mating could only occurr "to an extent," like with horses and donkeys?
I am not sure what "to an extent" really means in this context, but modern-day Europeans and Asians have some distinctly Neanderthal and/or Denisovan genes. So, unlike mules, the children of (anthropologically modern) humans and Neanderthals were able to reproduce.
In particular this has led some biologists to a rethinking of the Homo sapiens species as being many different (mostly extinct) subspecies:
- Homo sapiens neanderthalis
- Homo sapiens denisovan
- Homo sapiens idaltu [1]
- Homo sapiens sapiens (all currently living humans)
An important disclaimer, as without context this stuff comes uncomfortably close to racist pseudoscience: compared to every other living species of primate, there is vastly less genetic variation among humans. This is despite the fact that there are far more humans than there are chimpanzees, gorillas, etc. Among the common chimpanzee there are many different subspecies, with distinct genomes. Chimpanzee subspecies are physiologically capable of cross-reproducing, but have intense social barriers that prevents it from happening in the wild (except in cases of rape).
By contrast, modern humans only have one subspecies: Homo sapiens sapiens. Genetic differences between human groups are extremely subtle compared to chimpanzees, despite greater physical variation, and even the most bitter ethnic conflicts are nothing like the ancient socio-biological barriers found in chimps (they are transient on a biological timescale, and individual social/sexual relationships can still survive and flourish). So the ancient world of modern humans, Neanderthals, and Denisovans should really be seen as an ancient world with a variety of Homo sapiens subspecies, in an era where are genome was as variable and chaotic as the modern chimpanzee.
What specifically happened to the Neanderthals and Denisovans is an open question, though their minimal contribution to European and Asian genomes suggests they weren't around very long as a distinct subspecies once modern humans came over from Africa. So, going back to "to an extent" - the children of modern humans and Neanderthal were biologically successful from the perspective of Charles Darwin, but a culturally disastrous from the perspective of a Neanderthals.
If you are just taking a snapshot in time, that might just work. The problem over time, however, is that the descent, of each species so defined, is a long chain of breeding. There is a sorites problem in dividing it up into one species begetting another, as it is unlikely you will find offpring that could not breed with their parents' generation.
IMHO, the today's historians and archeologists have become just another type of beancounters. If I were to research this topic, I'd look into the RapaNui island, the strange statues on that island and the sudden cutoff of history records about 12,000 years ago.
"The number is mounting, and it'll vary depending on whom you talk to," said John Stewart, an evolutionary paleoecologist at Bournemouth University in the United Kingdom. Some researchers argue that the species known as Homo erectus is in fact made up of several different species, including Homo georgicus and Homo ergaster.
"It's all about the definition of a species and the degree to which you accept variation within a species," Stewart told Live Science. "It can become a slightly irritating and pedantic discussion, because everyone wants an answer. But the truth is that it really does depend."
It is very interesting to read how Hesiod defined the extinct species (size, anatomy, behaviour, etc) almost 3000 years ago and contrast it with modern research
I’ve always found this “humans are so stupid” meme a bit hard to fathom. As far as we can tell (so far) humans are by far the most intelligent thing in the universe. By what standard are we “stupid”? It seems to me to be equivalent to saying “blue whales are so small”, just because I can (approximately) imagine a larger animal.
In fact all you can reasonably define is survive-ability of a typical organism of a species to define it's success compared to other species. That is the only meaningful comparison that can be made.
Intelligence as we commonly define it is only a tool for survival.
While the fine distinctions in defining and counting species are interesting, it seems that a key issue is related to the Fermi Paradox, Drake Equation, and the Great Filter question.
How many separate times did potentially technological-level intelligence arise separately (and how separately)? Is it fairly likely to arise from a range of environments and evolutionary paths, or is the evolution of technological humans an absurdly unlikely fluke?
Are these multiple potentially technological species likely, and once one species gains technological advantage, it just dominates, or did just one 'branch' arise, most of the 'twigs' die out, and we've been just a bit more lucky so far?
My guess is that the more branches, and the further back in the tree they occur (i.e., further back than higher intelligence develops), the more likely it is overall that we are not alone, but we'd need a lot more information to make that call.
