Read it. Astonishing to not read what I would have expected: larger animals may have larger brains then smaller animals as an extra gram of brain has a smaller impact on e.g. the amount of energy to keep it working. (To clarify: suppose a powerlaw exists: to be equally 'smart' one needs a brain the weight of A*(mass)^B, with A and B constants, e.g. B being 0.3. The 'cost' of having that brain is then much smaller for a large animal, so it can grow a larger brain without the energy needed to keep it going being (percentage wise) larger then the smaller animal.)

And how about evolution: that really smart fish with twice the brainpower of the equally sized fish just vanished, as it did not compete energy wise with its competition.

Indeed, humans may be special in that babies are more and more just enough developed to be born, so that they just can be born through normal labour.

These two simple notions (perhaps not explained perfectly in a single comment) are absent from the article, and hence I felt something missing;-)