To add a little more to the conversation my understand is that grassland
ungulates actually do very little sleeping because there is no safe place
for them to go - they stand, semi-awake in open fields ready to run if
there is danger. (Then how can drunk frat guys sneak up on them to tip
them ?)
One position re: humans is that they have no defenses ( no speed, no
hoofs, no claws, no sharp teeth) so they, particularly, are better off to
hide and sleep when it gets dark.
