Anyone struggling with the Big Brain essay will find this site really useful. It's produced by Mc Gill University, based in Montreal, Canada. It has pages on the relationship between brain size and body size , the relationship between brain size and intelligence (here thought of as behavioural complexity), and changes in brain size over evolutionary time. It is especially useful because it presents in a visual way the kinds of evidence that evolutionary psychologists have used to support their theories about the evolution of the human brain. Useful stuff for evaluation.
You need to play around with the site a bit. It's organised into topics, levels of explanation, from beginner to advanced, and levels of organisation, from the molecular to the psychological. What's really important is that you roll your cursor over the square buttons to the left of the page. Some are red, blue, and yellow. The blue and yellow buttons are the important buttons for the big brain stuff. This is where you will find a lot of the really meaty stuff.
For everyone else there is loads of useful stuff on Memory, Mental Disorders, and Sleep and Dreams.
Link to The Brain from Top to Bottom