I am not aware of any brain weight comparison studies, but this digest of a particular hormone experiment does mention a higher preference for short term relationship - cognition inn those with higher levels of blood testosterone.

For better insight into the fact that other animals are not "dumb" please explore Conn Slobodchikoff et al. on prairie dog language, with its concise measurement of response to differently clothed humans, and other semantic-type variables.
Cetacean studies also seem to show very voluble animals other than Homo, transferring information, often very precise information, including instructional communications.

Female humans, by the way, are rather high in testosterone compared with females of a great number of other mammals, and experiments with testosterone and cognition suggest that it is involved with positive affect as well as physiological anabolic effects. The highest known BT occurs, insofar as I know, in Carcharhinus leucas.
Additionally, male canaries, as everyone who's taken basic animal behavior knows, grow parts of their brain involved in song production, singing in response to testosterone.

For those desperately anti-crotch, there remains elective surgery, which, in light of experiment and therapeutic use of testosterone precursors and therapy, has interesting effects outside of that tiny area, which can be quashed with a flick of a scalpel.

Finally, epigenetic modulation of behaviors are more likely to be proximate causes of behaviors than are complex and confused ideations. It may be that the crashing of fictions in one's mind concerning testosterone, once thought relegated to scientifically primitive era of decades past, can modulate - reduce - testosterone, perhaps leading to violence wherein only 50% of contenders may subsequently experience an increase.

This latter phenomenon has been quantified in sport, and even among nonparticipants adhering vicariously to imagined coalition with participants.

Since the species seems to be increasingly hell-bent on violent dispute, behavioral researchers should take to opportunity to gather blood samples for longitudinal studies of , well, inflammatory internet commentors, for one group.

More ultimately, human violence served a valid dispersal purpose, at least until the species became sedentary, creating agricultural city-states, which activity coincided with the diminution of mean brain size of 15% or more (some research claims near twice that loss). In other species social instability by aubadults caused their preference for dispersal, and thus, to misquote from Shakespeare's Portia pled, and ecological scientists might agree:
"The quality of [discord] is not strained;
It droppeth as the gentle rain from heaven
Upon the place beneath."
-for it reduces the excess population, perhaps one day to levels balanced with habitat. No biological occurrence is likely to have merely one effect, and those who seek to invoke the Statute of Winchester upon scientists in order to eliminate them from the population would do well to explore Portia's summation of claiming either reason to hate or misattributed vengefulness as "justice":

". . . consider this,
That, in the course of justice, none of us
Should see salvation . . ."

It is wise to temper internet comment, especially on any scientific discipline with which one is unfamiliar, for that science has at the very least, made the survival of every individual far more likely than it had been previously.

Or, in the words of an irascible ethologist versed in ecology: Don't comment about things concerning which you have no knowledge or care.

This is particularly apt for comments about social sciences and as it seems, on this site, which attempts to inform and help the public. It is not intended as a forum for vague vituperation, and should contain some comment flagging link to prevent its becoming such.