Being male isn't always what it's cracked up to be. Even in humans, an excess of males at birth turns into a deficit in old age. An example of one of the many possible dangers of being male comes from a study of the Eastern Packrat, a close relative of our Chihuahuan Desert packrats. The results almost certainly apply to our local species.
Packrats commonly have several young per litter. Raising a litter is, in the best of
times, an energy-draining ordeal, and when food is limited, not all members of the
litter can be supplied with milk. The choice becomes one between losing all of the
litter or of saving some young at the expense of others. Taking the last choice, the
packrat mothers neglected some offspring in favor of others. The neglected ones, many
doomed to an early death? Males! This makes perfect sense evolutionarily. Packrats are
polygynous, meaning that some males have a harem consisting of several females. With no
necessity for a one-to-one sex ratio, it's the superfluous males that must
go.
Contributor: Arthur H. Harris, Laboratory for Environmental Biology, Centennial Museum, University of Texas at El Paso.
Desert Diary is a joint production of the Centennial Museum and KTEP National Public Radio at the University of Texas at El Paso.