Neanderthals had bigger brains than us
There are hypotheses that Neanderthals were actually smarter than our other ancestors, and that they were wiped out for various reasons unrelated to intelligence. They may have been less violent than homo sapiens or seriously weakened by pathogens that didn't affect homo sapiens.
Don't know why I felt compelled to share this here, alas, there you go.
Wikipedia says modern humans have somewhere between 1% and 4%.
However, a smaller brain might have been better at that time. For example, a bigger brain requires more energy.
On the other hand, death in childbirth was a major hazard for females. Although I think Neanderthals' brain size at childbirth was similar to that of modern-day babies - but later it grew faster.
Were humans around at the time of the dinosaur extinction event?