I think they were also physically larger. Having a larger brain is good, but the brain is also the single largest consumer of energy in the body. It uses about 20% of the energy intake of a modern human and that's even with all the adaptations that came along to keep it under control.

The reason why I tend to go with the jaw is mostly because it's a reasonable place to spot it. The things that happened before that didn't really make much difference other than enabling later changes to occur.

Think of a car, the wheel was there for millenia before the car was invented, and there were cars before the internal combustion engine was developed, some of them were steam powered and I believe there was even a battery powered model, but until the internal combustion engine was added, you didn't really have what we would consider to be a car.

Oh, I understand what you mean. I hope I don't seem like I just want to be argumentative? 'Cause that's certainly not my intent.. I'm just, you know, stating an opinion...
I guess where we're not quite agreeing is that I wouldn't consider one single thing the reason for the development of human intelligence. The skull being big enough to accomodate a bigger brain - sure, but what do we need the brain for? My point being, there needs to be a reason for a physical change to manifest in a whole species (not only in a single individual). And as you said yourself, a brain is very expensive (energy-wise), and it's not only the size that matters.

Anyway, I looked up "evolution of human intelligence" on wikipedia, quite an interesting read, and some nice theories about monogamy and boobs as well :)

I think it's best not to think of evolution as having a plan. it's just that the genetic change can cause either a positive, neutral or a negative outcome to the individual.

I have heard the idea that with the introduction of cooking mankind was able to better digest the nutrients conducive to bigger brains

Nothing stirs up a good fight like politics and religion. People are always willing to show how ridiculously petty they are to prove they are right about meaningless tripe.

I actually wrote an essay on this back at university - came to the opposite conclusion though. For one thing, the increasing ease of global has meant that previously pretty isolated gene pools are now getting mixed up. Children Of Prometheus by Christopher Wills is a pretty good book on the subject.

Oh, and just found this - pretty cool. Evolution demonstrated in a lab!
http://en.wikipedia.org/wiki/E._coli_long-term_evolution_experiment

Baboons have started adopting dogs

Evolutionary regression due to incest - walking on all fours again
The mentioning of short tails, dense fur and additional nipples on some humans is worth further investigation too.

I think the core of evolution is that the "weak" - meaning unsuitable genes dont survive. The "better" genes are instead passed on more frequently and thus increase in genepool.

In our society having superior "health genes" or IQ 250 doesnt really make it any easier to pass on those genes on scale that matters. And even if you do pass them succesfully on - there are plenty people with IQ say sub100 and bad health who can keep themselves alive with modern medicines and pass on those "inferior genes" - to as many babies as possible.

Thus in my very non-expert opinion gene pools do and will mix up, but it is not likely that even very benefical genetic mutations born from these would increase in our genepool enough to cause "benefical" evolution in humans.

Most of the world has so much medicine and such standard of living (food for example) that it isnt nature anymore that would weed out those "weak genes" so to speak.

Then there are ethics - there are parents who want knowingly pass on "bad" genes to their childred. I remember some article about couple people who had this gene that they were very very small and they were asking doctor to make sure their child would have that same gene and NOT grow like normal people. I see the "human" aspect of such wish, but i personally dont think its quite fare for the child.

** Oh and just for clarification, i am not some nazi superhuman fanatic or anything.