Fitness affects sex

There are plenty of pressures on parents these days, especially expectant mums. You need enough omega-3 fatty acids for baby’s brain development, you have to prepare your “nest” appropriately, you need to be reading the latest parenting book with all the answers, and your diet and lifestyle generally needs to be a balance between that of Buddhist monk and an Olympic athlete. Now you can add to that the notion that your evolutionary fitness could impact your baby’s sex.

The role of the mother in determining baby’s sex has been highlighted in a new study of the broad horned flour beetle (Gnatocerus cornutus). As their rather descriptive name suggests these beetlies like grains and so are often found in flour mills and the male of the species does have enormous (proportionately) jaws.

There is however, a wrinkle in the evolutionary fabric of the broad-horned flour beetle’s existence.

Male flour beetles with the biggest jaws win the most fights and have the most mating success and are therefore seen as “high quality”. The problem is that to carry these huge jaws the males need muscles and a distinctive body shape. However, if this body shape and type is passed on by a big-jawed high quality father to his daughter, then that daughter will have a body type that is less efficient at carrying eggs. So successful fathers will have daughters who produce fewer offspring which kind of defeats the purpose of dad’s big-jawed heroics really.

In the broad horned flour beetle world this is balanced by high quality daughters, fathered by poor quality males, producing small jawed and weak sons but high quality females who produce lots of offspring. You only have to look at the British peerage to see this in action in the human world.

The pay-off for the high-quality dads is that although their daughters have fewer offspring they produce high quality grandsons.

So a high- quality, fit female will have lots of daughters, and poor quality females will have lots of sons.

Although generalising from the broad-horned flour beetle to the human experience might seem fraught with perils, there are certain evolutionary lessons to be learnt here. Mothers and fathers, impact their children in numerous ways and if that genetic conundrum is ultimately too twisted to untangle. So just be the best you that you can be and the kids will be fine.