Why Age Doesn't Matter For Motherhood

Published in the journal The American Naturalist, the study examined how burying beetle mothers instinctively adapt their prenatal and postnatal care according to their age. In many species, offspring birth weight and survival is affected by the age of the mother.

Human teenage mothers’ newborns are usually smaller and less healthy, for example, and young burying beetles mothers’ babies are similarly disadvantaged. This research shows that a range of parental activities, from the allocation of energy to eggs to the amount of time spent on care, varied between beetle mothers of different ages.

“In most species, there are reasons why a mother does not reproduce at the optimum age, whether that is because she has not yet met a suitable mate or food resources are scarce,” said Professor Allen Moore of the University of Exeter. “To cope with this fact, it seems that species have evolved to adapt their parenting to their age. We suggest that there is not one optimum age for motherhood.”

Burying beetles readily care for each other’s offspring. The research team switched the offspring between burying beetle mothers that first reproduced when they were young and only just sexually mature, or older than average. They found that age at first reproduction influenced the size of the babies at birth, with younger mothers having smaller offspring.

Some mothers adjusted their parental care to compensate for this. However, this only occurred when their foster babies came from mothers of the same age, suggesting that the rate of care is innate, rather than based on signals from the young.

Although they focused on beetles for this study, the group believes their findings could have relevance for other species, even humans. Professor Allen Moore said: “Insects are ideal for testing theories like this because, although they are fairly simple organisms, what works for them so often applies to other species. It makes evolutionary sense for the window for motherhood to be as wide as possible, giving the best chance for reproduction. We see no reason why our results could not be applied to other species, including humans.”