Lions and Hyenas would leave huge piles of bones in the middle of the dessert which had been picked clean by vultures.
One of our ancestors had the brilliant idea to use a rock to bust open the bones.
Wait - I thought hyenas were specifically bone-busting / eating:
"Spotted hyenas are some of Africa's most proficient predators. A frenzied scrum of them can dismantle and devour a 400-pound zebra in 25 minutes. An adult spotted hyena can tear off and swallow 30 or 40 pounds of meat per feeding. Latecomers to a kill use their massive jaw muscles and molars to pulverize the bones for minerals and fatty marrow. Hair and hooves get regurgitated later. "The only thing left is a patch of blood on the ground," says Holekamp." [1]
Note that the part you quote talks abut the latecomers to a kill going for the bones. That suggests that maybe hyenas don't like the bones, but will eat them if they aren't able to get the better parts of the kill.
Another part of that same article, talking about a rare hyena that made it to old age, mentions "She still had perfect teeth, too, since her rank assured her the best cuts of meat, whereas the teeth of lower-ranking animals get chipped and worn from crunching bones", which fits in with the bones not being something that they actually want.
So maybe if an animal is killed by a hyena pack that is small enough for everyone to get a good chunk of meat, they leave the less desired bones behind?
Brains are only developed if there is an advantage and I guess a brain without fingers, our eyes etc isn't maybe as useful as using the fat for energy.
Yp, brain uses tremendous amount of energy so there's a cost. Use too much of it to build the brain and you starve...use too little and same result since you're outsmarted. Rinse repeat until it's perfected.
Evolution doesn't converge for all species to some single point. It was enough that hyenas got adapted to their environment, and their mutations didn't make much difference towards larger brains.
One of our ancestors had the brilliant idea to use a rock to bust open the bones.
Wait - I thought hyenas were specifically bone-busting / eating:
"Spotted hyenas are some of Africa's most proficient predators. A frenzied scrum of them can dismantle and devour a 400-pound zebra in 25 minutes. An adult spotted hyena can tear off and swallow 30 or 40 pounds of meat per feeding. Latecomers to a kill use their massive jaw muscles and molars to pulverize the bones for minerals and fatty marrow. Hair and hooves get regurgitated later. "The only thing left is a patch of blood on the ground," says Holekamp." [1]
1 - https://www.smithsonianmag.com/science-nature/whos-laughing-...