Phrenology has had its adherents over the years, none that I know of were successful in proving any real predictive power though. Brain size and intelligence s

Phrenology has had its adherents over the years, none that I know of were successful in proving any real predictive power though. Brain size and intelligence seem to only be correlated in the loosest of ways anyway. Everything we know about performance of information processing systems says that their size and weight is almost irrelevant compared with their design. We expect simple algorithmic optimizations to provide orders of magnitude of improvement, and more advanced ones to provide more orders of magnitude on top of that. If I recall rightly the metric with the best performance is ratio of brain to body mass. This would make sense if you assume that brain performance is determined largely by its 'design' and scales only modestly with mass, and that creatures of the same species share the same design.