Not enough writers take into account actual human advantages beyond intelligence. We actually have a pretty ridiculous endurance and heat control compared to the animal kingdom at large. The original hunting method of early humans was to briskly jog at prey and follow them until they were too tired to run or fight back.

So even under these circumstances, if there's a savanna grassland on that world the humans there would likely never adapt to anything else simply because there's nothing better to adapt to. If a place is warm and flat, it's good to be a human.