Generally speaking, intelligence can be (roughly) measured by comparing the 
size of the brain to the body, and forming the appropriate ratio. So, if you 
have two hominid species of a similiar size, but one has a bigger brain, you can 
be sure that that one will be more intelligent, as a species, than the other.

However, here's more data re Homo Erectus and other hominids which clinches 
the issue that their their intelligence was increasing in tandem with growing 
brain-size:-

"Homo erectus, or erect man, appeared by around 1.8 million years ago. The 
most significant difference between Homo erectus and the previous species is 
the large increase in their cranial capacity. Throughout the existence of homo 
erectus, their cranial capacity increased from approximately 750 to 1250cc. 
This expanding brain case came to dominate the shrinking face, and foreheads 
began to develop in the later members of the species most likely as a result of 
a growing frontal lobe. The frontal lobe is the part of the brain that controls 
many of our higher functions such as foresight, concentration, and reasoning. 
Homo erectus had heavy teeth, thick eyebrow ridges, a receding chin, and 
stood about 5 feet and 6 inches tall."

taken from:-

http://tinyurl.com/5ghz79

Geoff

On Thu, 15 May 2008 10:46:14 -0500, Paleogal <[log in to unmask]> 
wrote:

>----- Original Message ----- 
>From: "Geoffrey Purcell" 
>
> As a consequence, the 
>frontal and temporal lobes of their brains were narrower, suggesting that 
they 
>would have had somewhat lower mental ability.
>
>
>taken from:-  http://anthro.palomar.edu/homo/homo_2.htm
>
>Geoff
>
>
>On Wed, 14 May 2008 11:29:34 -0500, Paleogal 
><[log in to unmask]> wrote:
>
>>> Geoffrey Purcell wrote:
>>>>
>>>> As far as cooking is concerned, it's already been pointed out that the
>>>> average hominid brain-size heavily expanded in size long before cooking
>
>This doesn't necessarily mean that bigger is better.  Depends on the location 
in the brain.   Oliva