Why did our ancestors become bipedal? The idea that they learnt to walk on two legs to escape from predators, or to help them use tools is no longer accepted. This is because two-legged walking is less efficient at high speeds than four legged walking, so when being chased by a predator is not the best time to learn, and why learn to go on two legs to learn about tools when you don't know what a tool is?

If an ape could move away from the extreme 'K' reproductive strategy, it would have more chance of survival. The trouble is, apes are in a complex feedback loop, 'pushing' them into the extreme 'K' strategy. It can be thought of like this.

If you are to raise only one child, and raise it well, you must be a good mother. This means, a higher IQ is needed, which means a better brain development. This requires a much higher investment in the future mothers in the uterus, so less energy to spend elsewhere, so less children can be produced, which leads to a more severe extreme 'K' strategy, and so you must be a better mother.....

This is tied into another feedback loop. If the infant has a large brain, it will have a higher IQ, and it will need stimulation in the form of playmates, which means a social system must be in place. If there is a social system, a higher IQ is needed to learn ones place in it and all the rules. This needs a higher IQ, so playmates are required.

Bringing this into terms of human evolution, it is noticed that the very first australopithecine's were bipedal. So, they must have developed this before leaving the forests. What use is bipedality in the trees?

The answer can be seen by thinking about the disadvantage of a severe 'K' strategy. The main disadvantage is the low birth rate. How could birth rate be increased? By looking after more than one child at a time. If one does do that, then there is a much greater food requirement, so more co-operation is needed. This means that the male must go and get the food while the female stays in one place. Limited mobility means that becoming bipedal can happen, even though, as we have seen, it is more inefficient. If a female is walking on two legs, she can carry more than one child, and the male can carry more food back to the female.

How can animals become more co-operative, especially when we are talking about males and females in a group together? Most fighting between males takes place over females in heat, so if there is no set time for a female to be ready for mating, then there is less competition. Another problem is how can a male trust a female why he is away? It is possible that as he will find another partner and have other children. This can be solved by pair bonding. Making animals choose one particular female more than the others. This is like falling in love. Something that other monkeys/apes do (apart from some chimps, who will leave the group for a 'honeymoon' for a period of some weeks).

So, higher birth-rate, more social bonding, higher IQ all go hand in hand with being bipedal. Once out on the savannah, already bipedal, then it can be used to the animals advantage. When, during the Miocene/Pliocene the forests started disappearing, the upright apes would have been the best suited (and most numerous) of the apes to fit the new niche.