Children who look and smell like their father receive more of their support, compared to kids who resemble dad less.
The study of 30 Senegalese families has provided the first direct link between a father鈥檚 investment in his children and his physical resemblance to them, though other work has hinted at this connection.
For instance, a study conducted at London鈥檚 Heathrow Airport found that fathers invested extra time and money in children who looked and behaved like them, compared with dads who said their kid鈥檚 looks and personalities differed from their own.
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Such uncharitable behaviour may seem shocking, but evolutionary theory predicts it. Without a DNA test and an appearance on the Jerry Springer Show, a father can never be absolutely certain that a child is his own.
Therefore, it makes evolutionary sense to divvy out limited resources 鈥� be they time, food or money 鈥� to children more likely to be legitimate.
Who鈥檚 the daddy?
The behaviour has an evolutionary advantage because there are always going to be illegitimate children, says , a biological anthropologist at the Institute of Evolutionary Sciences in Montpellier, France, who led the new study.
A 2006 paper estimated illegitimacy rates at between 0.8 per cent and 30 per cent among different populations around the world, with an average of 3.3 per cent.
Alvergne did not know the paternity status of the 60 children involved in this study, but she guesses that a couple of them could have been illegitimate. Yet because she and her co-authors were interested in the perception of father-child resemblance, actually paternity did not matter.
Watch and sniff
To determine which children looked and smelled most like their fathers, Alvergne鈥檚 team systematically involved more than 100 people from a distant village, who were not familiar with the kids. These 鈥渞aters鈥� were asked to match a child鈥檚 digital image to an image of one of three potential fathers. For smell, villagers sniffed a T-shirt the child had worn for a night and compared it to T-shirts worn by two potential fathers.
They correctly matched the child to the right father based on photos half the time, which is well above chance. But only men picked out fathers based on T-shirt smell at rates above chance, the researchers found.
The team next compared these ratings to an objective measure of paternal investment, based on the time fathers spent with each child in a day, a standard psychological questionnaire of father involvement, and a survey of financial and emotional support.
Children that looked and smelled more like their fathers tended to receive more paternal investments, Alvergne and her colleagues found. Factors such as a child鈥檚 age, sex, or birth order did not predict fathers鈥� investments, nor did the father鈥檚 own age or wealth.
Moreover, after accounting for age, children who received additional support from their father tended to weigh more and have thicker arms 鈥� both indicators of good nutrition 鈥� compared to children who got less fatherly support.
鈥榃ham, bam!鈥�
It makes sense for fathers to apportion their efforts wisely, says , an anthropologist at the University of Oklahoma in Norman
鈥淗uman males do spend a lot of time investing in their kids and they invest quite heavily,鈥� he says. That is a sharp contrast with other mammals, including our closest primate kin. 鈥淚n 90 per cent of mammals, a father鈥檚 investment ends in ejaculation 鈥� wham, bam, thank you, ma鈥檃m!鈥�
, an anthropologist at Florida State University in Tallahassee, thinks fathers in western cultures probably act the same way. 鈥淭here鈥檚 no reason to think that they鈥檙e going to find something very different here.鈥�
In unpublished work, Alvergne says her team has found that western fathers invest more in children that resemble them, though improved nutrition probably doesn鈥檛 explain the investment as it did in Senegal, she says.
However, a recent long-term study of English fathers and children found that the more time a father spent with his kids, the more successful they are as adults.
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