My problem with the notion that humans caused the extinction of large mammals is that humans supposedly originated in Africa and large mammals weren't extinct there. So how did that happen?
It's also not as if we have evidence of large populations of humans in the glacial era. You would need a modern civilization with at least metallic tools to spread far enough and wide enough to kill off multiple major species.
Doesn’t the dodo show that that isn’t a given?
During the age of sail whenever a ship would land on a new island they local animals could be plucked like fruit because they didn't fear humans.
The results were always quite predictable.
In the ice age the tools were bone and stone. And the lack of agriculture meant that human populations were kept small by available resources by default. The lack of transportation or even domestication of animals in the Americas at the time meant that all travel was on foot. To dominate species like the mastadon, giant ground sloth, cave bear, dire wolf, etc on two continents was just something humans weren't capable of at the time.
Hunting was still risky and labor intensive. Arrows didn't have metal heads. Range was limited. Traveling was risky, both from natural and tribal threats.
It just doesn't add up. The density of humans was probably lower in the Americas than in any other continent (save for Antarctica of course).
We know humans spread far enough and wide enough in stone age times. Big animals reproduce slowly, and the extinctions happened over centuries or millennia. Metal tools and large populations weren't needed, just stone age hunting techniques and persistence.
The extinctions correspond to human arrival everywhere homonins weren't already established: https://ourworldindata.org/quaternary-megafauna-extinction
We actually don't know precisely when the extinctions occurred or how long it took for them to occur. All we know is where the gaps in the sparse data set that is the fossil record exist.
It could be that the extinctions actually made it easier for humans to expand and move into those areas after the fact, or that humans uniquely benefitted from the environmental or situational changes that were ongoing.
We know the Younger Dryas was an incredibly intense era of climate change, after the ice age receded it suddenly plunged back into glacial temps for a millenia or two. Very strange and stressful time for species of all types.
We didn't need to hunt dangerous saber tooth cats to get them extincted. We had only to hunt their less dangerous food. They probably couldn't live off the small prey left after the human wave swept the continent.
Megafauna extinction is closely timed with the arrival of humans on just about every continent or island we happened upon. Even Africa is relatively more depauperate compared to the distant past.
Of course not all of them found their end. There are still moose in North America, and giant tortoises in the Galapagos that literally floated away from the coast of South America, where they later went extinct. But there are fewer everywhere.
But this is an ideological and political issue, not a scientific question. So case closed, the Consensus Is Settled.
Sure, but the arguments against are in the same vein as the argument that, if I draw a circle, it's not a real circle, because I don't have the level of fine control over my hand that would be necessary to produce one of those, and the tip of my pen is too wide.
True, but not really relevant to anything, and in particular unlikely to convince anyone that it's a mistake to call what I drew "a circle".
https://www.edge.org/conversation/christopher_stringer-rethi...
I'm sure this is ignorant, but: if two individuals can interbreed and produce fertile offscreen, then aren't they, by definition, the same species?
No. For example, that would make it impossible to determine the species of fossils.
For another example, wolves are considered a different species from dogs, and coyotes are considered separate from each.
For a third example, bacteria don't interbreed at all, but we don't consider each of them to be their own species.
The definition you allude to is technically known as the "biological species concept", which should be a hint that it's not viewed as definitive.
But there are several good reasons; their behavior, life strategy, and often size and appearance are all radically different. The best match here is probably the "ecological species concept": (1) https://www.blackwellpublishing.com/ridley/a-z/Ecological_sp... ; (2) https://en.wikipedia.org/wiki/Ecotype
> and what species are the offspring of a dog-wolf mating considered?
I am not personally aware of standard terminology, but I might say "half wolf" or "wolf hybrid". The wikipedia page is titled "wolfdog". https://en.wikipedia.org/wiki/Wolfdog
There is standard terminology for the offspring of a wolf and a coyote; those are called "red wolves". Wikipedia suggests that they have a taxonomic species name canis rufus, but this is controversial (since they're hybrids).
Turning it around a little: if some members of a mainland species move to an island and eventually become incapable of interbreeding with the original species, then it is always a new species. True or false?
So "no-interbreeding" is sufficient but not necessary?
I think people would basically agree with this; true enough.
> So "no-interbreeding" is sufficient but not necessary?
Not quite; the example of bacteria, above, disproves the sufficiency of "no-interbreeding".
(Bacteria do mix their genetic material, but they directly exchange it with each other, and then their children are clones of themselves. Imagine if, whenever you had sex, your partner took on some of your traits, and you took on some of theirs. This would obviate the need for your children to draw their traits from more than one parent, and that's how bacteria work.)
There are asexual higher organisms, like some lizards, and they follow the taxonomic example of bacteria in that when two of them are genetically similar enough, we call them the same species despite the fact that - since they can't breed at all - they cannot interbreed.
The fossil example is also incompatible with "no-interbreeding" being a sufficient criterion, though this is a bit less clear than the bacteria example; we can't determine whether two fossils were or weren't able to interbreed. We can be nearly certain that there is some pair of structurally similar-looking fossils out there that we have labeled as belonging to a single species, despite the fact that the individual organisms wouldn't have been able to breed with each other. You could make the argument that this is simply a mistake on our part, and that would have a lot of validity, but even viewed that way it's a mistake that cannot even theoretically be corrected, which causes some conceptual difficulties.
The reason there are so many species concept is that species are just a reflection of the idea that two organisms are "the same". What it means to be "the same" varies in different contexts, according to, without claiming to be exhaustive, (1) what you care about; (2) what is possible in the space you're discussing [pigs can't do the direct genetic exchange that bacteria can]; and (3) what it's possible for you to know.
> I do appreciate this and I hope you don't perceive it as "arguing."
Don't worry about offending me; you seem to be in perfectly good faith so far.
Incidentally, today on Facebook someone made the risible claim that since our DNA is 98% the same as a chimp, WE are "98% the same as a chimp."
I pointed out that by that standard, we're also 60% the same as a banana.
https://en.wikipedia.org/wiki/Ring_species
This parallels the phenomenon you see in languages where, for example, any two adjacent villages across a considerable distance will be able to speak to each other, even though villages at opposite ends of the continuum cannot do so.
(The "ring" part of the term refers to the two ends of the interfertility continuum being located in the same geographic area, which is a red herring.)
As the wikipedia page notes, the problem that this concept exposes is that interfertility is not a transitive relation, and therefore can't be an equivalence relation.
> today on Facebook someone made the risible claim that since our DNA is 98% the same as a chimp, WE are "98% the same as a chimp."
> I pointed out that by that standard, we're also 60% the same as a banana.
The major problem here is that "to what degree is a person 'the same' as a chimp?" is not a well-defined question. Again, you would need to define what it means to be the same, and it will vary with what you care about.
There are important ways in which we are the same as a banana; most obviously, you can eat a banana and expect to be nourished. This is not a given for an alien organism, even one that appears to be largely chemically identical to a banana. Whether the similarities reach 60% depends on how you convert them to numbers. We can note that the concept of 'species' assures us that any two humans are 100% "the same", as compared to a banana, whereas if you research relatedness the convention is that two brothers are 50% "the same" and two strangers are 0% "the same" (and bananas, not being human, don't exist), and if you're doing theology the convention is generally that even identical twins are 0% "the same".
Summing that up, if you're told that two things are the same, the response is "the same how?" The reason the Facebook argument is stupid is that total shared DNA count isn't a useful thing to measure for most purposes. The salience of a difference in phenotype isn't closely related to the amount of DNA that changed to enable it.
How could you have seen any if the entire topic itself is a political hot potato and verboten to even discuss?