Gimme shelter

Humans split from arboreal apes and became terrestrial apes, due to a chromosome fusion/inversion, probably simultaneously with the inversion of the standard arboreal ape bowl nest into the predecessor of the dome hut, the dome shield, a sort of umbrella of twigs and leaves. Sleeping endomed reduced the normal advantage of fur, being a rain-shedding sun-shading bug-screening camouflaged shield, mother & infant under one, father and toddler in adjacent one, and others sleeping around the base of an easily climbed escape tree if nocturnal predators came by. By 250,000 years ago, the fur long gone, a campfire replaced the tree as the focal point, by 50,000 years ago, sedentary dome huts (doorways) and gardening supplanted nomadic dome shields, though shields were still used eg. coracles, war shields, basketry…

Jeff Goldberg @Quora:
"While certainly plausible, I would be interested to know the argument for the “23 and human” merger being so closely tied to the move to the ground and use of ground-based shelters."

We see no arboreal apes with 23, only 24 chromosome pairs, indicating a permanent isolation, despite humans, gorillas, chimps and bonobos overlapping in econiche, diet & geography. Accompanying the change was the polarising division of limb and digit changes, longer arms and fingers & shorter legs in daily climbing arboreal apes, longer legs and thumbs & shorter arms in daily carrying-striding terrestrial humans. The dome shields were portable ground shelters, carried while foraging (basket) & hunting (camo shield), tilted up for shade for day naps, dug in for night sleep.
DD