I live in the UK and I am amazed that date palms do well here, in a country with much higher rainfall and it does get colder than the middle east. Also agaves seem quite happy (what tequila is made out of.

What's actually more surprising than cold tolerance is that water tolerance; desert-y plants tend to be adapted to be needing periods where their roots are dry for long periods. Let them stand with wet feet and many desert plants get very upset.

I guess the middle east was wetter even in roman times, so perhaps that answers part of that.

To flip the chicken question around a bit, it's perhaps odd that chickens can cope not with the cold but with their native heat so well, what with wearing a full-body, heavy down jacket all the time in their native tropical jungle.

My understanding is that they lose a lot of water through their skin. Not a deep enough understanding to know whether saying "chickens sweat a lot" is accurate, but I imagine in either case the evaporation helps them keep cool.

Bird feathers can trap air inside and can be raised all together in a second making it work like a sponge. A better analogy could be wearing a flask

Chickens molt! They rid themselves of the feathers and down periodically.

And then they grow them back again I presume. In the middle of a jungle forest. It seems odd.

Yes, and I get the advantage of clothes :-)

They don't even seem that bothered by it. If you put a heater in the coop they don't make a point of perching near it, for example. They hate the snow like it's lava though.

That depends which humans. We are not one monolithic gene pool. Human diversity means that more recent migrations of humans had less time to adjust to their new climates.

If you compare, say Inuit, Nordic, and native Siberian populations, to subsequent equatorial populations to higher latitudes, if you could find instances of low interbreeding, I wonder if we'd see certain genetic adaptations missing.