That is interesting. I don't think that you can say that the cause is our brain being squished during birth. I think the child lags behind at first because it has to do deeper learning and hence it takes more time. i.e. The brain is learning a lot more patterns, and patterns within patterns, than the chimp. Remember that a baby is also learning to speak. The child just has a lot more brain cells it needs to train. Although, a child at one year will already understand a lot of what you say, not sure about the chimp.