A study validates the hypothesis that in some fish species, females with larger brains possess better cognitive functions, which makes them choosier in mate selection.


In nature, all species are driven to propagate; this impetus is not simply to reproduce but to find the mate that can ensure the survival of the species. Males in the animal kingdom commonly exhibit traits that indicate the “robust-ness” of their genes—plumage for birds, or manes for lions are examples.  Courtships rituals are usually displays of these characteristics, but how do females actually choose? And are all things considered equal in making these choices?

A March 2017 article in Science Advances attempts to answer these questions by observing female guppies and how they go about selecting male partners. These females were presented with males demonstrating different gradations of color markings—the acknowledged secondary sexual characteristics for guppies. Their respective choices were noted and the brain sizes of the females were subsequently measured and recorded.

What the data shows is that the females with larger brain sizes would preferentially select males with brighter or better color traits, which translates to attractiveness in the species. In contrast, smaller-brained females demonstrated no discernible preference in choosing a prospective mate. From studying the fishes’ response to the visual cues (the Opto-Motor Response), the researchers were also able to demonstrate that the difference was not in the perception of color (which was equal throughout all females) but rather in the way the respective brains processed these indicators of attractiveness.  So, while all the females saw the same colors, only those who perceived it as an attractive trait made efforts to choose a mate.

Of course, human relationships are much more complex than simply males waving colors or perhaps flexing their muscles. There are obviously emotional and socio-cultural mechanisms involved in how courtship and mate selection (if at all) occurs in our species. However, this indicates that ‘smarter’ individuals do indeed recognize traits which can be seen as desirable for companionship and perhaps species propagation. Whether this is based on physical attractiveness, intelligence, emotional stability, parenting instincts, or financial status—it is the cognition of these traits which factor into the selection of a mate.

While it can be simplistic to study these choices in terms of guppies and their brain sizes, there may be some comfort for those of us who have been indeed chosen by our (smarter) partners.


Written By: Jay Martin, M.D.

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