Why were stone handaxes made in the same way for a million years?

Early man made some useful hand tools
And no-one could say they were fools
But the axes they made
They failed to upgrade
‘cause no-one could teach them the rules.

In considering the evolution of human intelligence there is uncertainty about when an effective language first emerged and there is also a mystery of the early stone hand axes, which were made to the same design for about a million years. If the early hominins who made these tools were really that intelligent one might expect that someone in more than 70,000 generations would have found a way of making better stone hand axes.

Why did the human brain stop growing when we started being creative?

 Recently Adam Benton posted an article " Fear drives technological evolution" on the Evoanth blog which started with the above picture. It shows some of the fanciest stone age tools our ancestors made; all of which were invented after our brain growing. He then asked: "What caused their development?"

  A very good question. Over a period of perhaps 4-5 million years the brains of our ancestors grew steadily from species to species and yet the advances in technology, as judged by stone tools, advanced very slowly, with periods of up to a million years where similar tools were being made with no sign of advancement. Then Homo sapiens appeared on the scene, with a brain no bigger that the earlier Neanderthals, and starting perhaps 150,000 years ago the surviving archaeological remains show changes at an increasing speed, especially after about 50 thousand years ago, with no apparent increase in brains size. When we started living in towns and then cities the rate of innovation rocketed to a point where we can pretty accurately date archaeological finds by the technology being demonstrated. However some recent research actually suggests that since civilization started our brains may have been getting smaller.  If you simply equate big brain with better technology this does not make sense.

Adam Benton, of Evoanth, tries to link advancing technology with fear - but I feel his arguments miss the point and I would suggest that the change was due to the advent of language, which enable us to develop far better ways of learning. I posted the following reply on Evoanth:

Chimpanzee Language - Is it a model for a primative language in early hominids

There has been a lot of online interest in the paper The Meanings of Chimpanzee Gestures by Catherine Hobaiter & Richard W. Bryne, which has just been published in Current Biology. The abstract ends: Here we present the first systematic study of meaning in chimpanzee gestural communication. Individual gestures have specific meanings, independently of signaler identity, and we provide a partial “lexicon”; flexibility is predominantly in the use of multiple gestures for a specific meaning. We distinguish a range of meanings, from simple requests associated with just a few gestures to broader social negotiation associated with a wider range of gesture types. Access to a range of alternatives may increase communicative subtlety during important social negotiations.

The researchers claim that they have decoded 66 different gestures whose meaning is the same whichever ape was making a gesture. For instance if a mother shows the sole of her foot to a baby it means "climb on me", while touching an arm is a request asking to be scratched. Interestingly chewing leaves is an invitation for sexual attention. Apparently several gestures can be strung together to represent more complex exchanges.

For the time being I feel rather frustrated, as the full paper is behind a paywall, and I would really like to assess the strength of the research for myself - rather than being dependent on the first wave of press release news reports. However there has been plenty of earlier work which establishes that a social animals such as the chimpanzee must be communicating, and I am sure that if there are any weaknesses in the current paper comments will soon turn up on various blogs elsewhere. 

However if wild chimpanzees in Uganda have a language of over 50 gestures it is interesting to  think how many gestures (or simple vocal sounds) would an early hunter-gather hominid need to be able to organise hunting by ambush or describing the location of a food source, in addition to normal social interactions. I would have thought a hundred different signals relating to actions and the ability to name a hundred objects would prove a powerful survival tool - and is not much more than appears to have been demonstrated in chimpanzees. Such a language could be far more primitive than the proto-language that is believe to have preceded all modern languages. 

Of course my estimate is only a guess. Has anyone done any research on the size of vocabulary needed to plan and execute a complex hunt?