I did not mean to suggest that autism could be traced to Neanderthal genes. The point is that some genes that have been implicated in autism changed pretty significantly between the time Neanderthal line and human line split.

We can't say that when x happens we get a mass extinction. To the extent we understand mass extinction, one has been caused by glaciation event, one has been caused by a massive climate change, and one has been caused by an asteroid. These events turn out to have no precedent.

Most of the world's major waterways have been diverted or dammed or otherwise manipulated - in the United States, only two per cent of rivers run unimpeded - and people now use half the world's readily accessible freshwater runoff.

There's this idea of shifting baselines. It was coined by a guy named Jeremy Jackson. It's the idea that every generation takes what it sees, and says, "Okay, well, that's the norm."

Neanderthals were pretty smart, and if we actively killed them off, then probably we did so in the same way that humans kill each other.

Some of these species that are now no longer with us were killed off by a fungal disease that was moved around the planet by people.

We have all this Paleolithic art that suggests that our ancestors really venerated animals and that they depended on wild animals to survive - as opposed to domesticated animals that we depend on. Would it radically change things if we had more rhinos in our midst? I kind of suspect it would.