Why did early humans walk upright? Owen Lovejoy of Kent State University has an intriguing hypothesis after studying the oldest human skeleton, of the species Ardipithecus ramidus or "Ardi" for short: it's all about food and sex!
In apes—both modern apes and, presumably, the ancient ancestors of Ardipithecus—males find mates the good old-fashioned apish way: by fighting with other males for access to fertile females. Success, measured in number of offspring, goes to macho males with big sharp canine teeth who try to mate with as many ovulating females as possible. Sex is best done quickly—hence those penis bristles, which accelerate ejaculation—with the advantage to the male with big testicles carrying a heavy load of sperm. Among females, the winners are those who flaunt their fertility with swollen genitals or some other prominent display of ovulation, so those big alpha dudes will take notice and give them a tumble, providing a baby with his big alpha genes.
Let’s suppose that some lesser male, with poor little stubby canines, figures out that he can entice a fertile female into mating by bringing her some food. That sometimes happens among living chimpanzees, for instance when a female rewards a male for presenting her with a tasty gift of colobus monkey.
Among Ardipithecus’s ancestors, such a strategy could catch on if searching for food required a lot of time and exposure to predators. Males would be far more successful food-providers if they had their hands free to carry home loads of fruits and tubers—which would favor walking on two legs. Females would come to prefer good, steady providers with smaller canines over the big fierce-toothed ones who left as soon as they spot another fertile female. The results, says Lovejoy, are visible in Ardipithecus, which had small canines even in males and walked upright.
Jamie Shreeve of NGM Blog Central has the story: Link
Maybe early humans lived in quite safe environments because our babies are so helpless, we move slow, can't really smell, and have small teeth. We lived so comfortable we even lost our need of fur. Maybe we kept each-other warm by laying together? Maybe we had sex all day (like Bonobos) because both males and females didn't know when the females were fertile. If only 'alpha males' would reproduce, as happens with most animals, the human race today would exist of large, strong, muscular men and big, fertile women. It's not at all like that, so maybe early humans didn't care much who spread his or her genes (or legs) as long as they were comfortable, and had sex anyway.
Because we were such social animals we started communicating, with gestures and facial expressions, later with speech and imagination. So today I can imagine what happened with women like Ardi en Lucy.
I'm not a scientist, I just love to think about what could have happened.
@ swss
what if you consider that the Savannah habitat required our ancestors to walk greater distances while carring the "engagement food."