Answer
a) The costs of having disproportionately large brains must be outweighed by the benefits associated with them in the lineages.
b) Natural selection could favor the evolution of disproportionately large brains if those brains increase survival, for example, by allowing animals possessing them to evade predators or find more/higher quality food.
c) Please see the image. From the slope of the best-guess best-fit line drawn, deviation from brain size and mortality are weakly and inversely related: there is some decreased mortality with increased brain size. It is possible that other benefits than decreased mortality come with increased brain size in birds.
Work Step by Step
a) This answer is based on the basic idea of evolution: beneficial traits are selected for by nature.
b) Use your imagination to see how a larger brain/better processing of information could benefit an organism.
c) Draw the graph as directed in the question. Note that the decrease in mortality is not great— this suggests that some other benefit exists.
