Big animals tend to have big brains, partly just because they are big. This does not mean in any interesting sense that they are cleverer. Elephants have bigger brains that humans but a probably with some justice we like to think that we are cleverer than elephants.~ Dr. Richard Dawkins (1941-03-26 age:76), The Blind Watchmaker: Why the Evidence of Evolution Reveals a Universe Without Design
I think Dawkins is over simplifying. Consider how small a brain a T-Rex needed. Human musculature is not that much more complex than a T-Rex. You need a sophisticated way to allocate brain power to running the body vs thinking. We humans as individuals are not that impressive thinkers. It is only organised in massive numbers embedded in culture do we do much clever. We are the analogy of ants. We tend to overestimate the thinking power of an individual human. Further it is our hands, not our brains that make us so good at manipulation and construction. The creators of systems of measuring brain capability fiddle the formulas to make man come out of top. What you really want is the weight of brain left over for thinking after dealing with controlling the body, sight, hearing/echo location etc. The absolute weight is what counts, not its ratio in any way to body weight.