Biologically speaking, men and women face at least one important difference when raising a child. Due to biological mechanisms, it is virtually impossible for a woman to unknowingly raise a child who is not (genetically) her own. I have never given birth to a child myself, but reliable sources have told that it is impossible to miss and impossible to forget! However, men have no such biological mechanism that insures that the child is their own. Therefore, men face paternity uncertainty, or the possibility of unknowingly raising a child who is not genetically related to themselves. In other words, they could be fooled into raising the child of another man.

Now, men can and do knowingly raise children that aren’t their own. Either as a step-father or as an adoptive father. This kind of altruistic care exists, and has positive moral implications. However, from a biological perspective, any care a man gives to a child unrelated to himself usually takes away from care he could give to his own children. To use an extreme example, the perfect altruist who only raises other men’s children will pass ZERO copies of his own altruistic genes into the next generation! That’s a bad ending from a biological persepctive.

Therefore, men should be more interested in whether a child is theirs (genetically) than women should be. Evolution “solves” current problems in the future, not the present. So if we want to look at current male adaptations, we have to consider past males. And in the past, men didn’t have DNA tests to confirm or DNA their paternity in front of a studio audience on Jerry Spring! No, men had to use other cues. One of the most likely cues was the behavior of the mother. However, the infant might have also offered cues. In particular, if two individuals share the same genes/DNA, they should resemble each other. Thus, men should be more concerned with resemblance to infants and children than women. Several studies of parental investment have supported this finding. We conducted several studies asking men and women how interested they were to hypothetically adopt an infant or child based on a facial picture.

We found that men placed a significantly greater emphasis on cues of resemblance when they made their hypothetical adoption decisions (the first comparison on the figure above- Volk & Quinsey, 2002). This supports our prediction, as well as the general hypothesis that men are more interested in cues of paternity certainty than women are interested in cues of maternity certainty. We replicated these results in 2007, finding once more a male-bias towards cues of resemblance. Later, with Dr. Marini and my M.A. student Carolynn Darrell, we found evidence (2010) that the relationship between cues of resemblance and paternal care may be bidirectional – fathers who spent more time with their infants reported a significant increase in their perceptions of resemblance as compared to a control group.

It is important to note that even if men possess such an evolved bias, it does not in any way justify the bias or decisions related to the bias. We firmly believe that any such biased can be changed and/or diminished through sincere care and effort!

At some time, in some situations, parents have been faced with the heart-breaking dilemma of not having enough resources to care for all of their children. Even now, starvation is sadly a very real risk for many children. When this happens, parents may have to choose between giving all the food to one child so that it can live, or sharing the food and risk losing both children. Ethically, this is an awful choice. Biologically, it’s isn’t a good choice either, but at least the answer is clearer. Biologically speaking, a parent should decide to invest their resources in the child that has the greatest chance of benefiting/surviving from them. To this end, facial cues of child health may influence parental investment decisions.

To investigate this possibility, we have conducted two studies to determine how adults respond to cues of low body weight, and cues of high body weight. By digitally decreasing or increasing the soft tissue on an infant or child face, we can simulate different body weights.

In accordance with our prediction, we found that faces with altered body weights received significant lower health ratings from adult viewers. The same faces were also rated as less cute, and less desirable for hypothetical adoption! This supports our hypothesis that child facial cues of health may influence parental investment decisions.

It is important to note that these appear to be unconscious biases, rather than deliberate biases. That makes them difficult to measure, and perhaps difficult to control. Nevertheless, we firmly believe that any such biases can be overcome by deliberate care and affection. Children with low- or high-body weight faces are not doomed to poor parental care! We simply believe that it is important that if these biases exist in real-life situations, adults should simply make the extra effort to overcome them.

Fetal Alcohol Syndrome is a serious developmental disorder associated with the consumption of alcohol during pregnancy. It is associated with significant mental and physical problems. One of the characteristics of Fetal Alcohol Syndrome is the facial appearance of children with the disorder.

As our earlier (Volk & Quinsey, 2002) work has shown, adult hypothetical adoption decisions are influenced by infant facial cues of health. Fetal Alcohol Syndrome shares many facial characteristics with other disorders. We therefore used it as a model for general faciocranial dysformities (i.e., abnormal looking faces associated with a medical condition). It was our belief that adults would prefer normal faces compared to FAS faces, and that they would prefer FAS faces digitally altered to appear normal over normal faces that were digitally altered to have FAS characteristics. Specifically, we altered the upper lip, the philtrum, and the eyes according to the standards for FAS.

Health face on the left, health face morphed to display FAS characteristics on the right

As can be seen from the manipulation above, our technique was very subtle. Indeed, adults did not consciously report noticing the differences, and even we had to break out measurements to tell all of the differences! Nevertheless, our predictions were supported by the data that showed a significant bias in the health, cuteness, and adoption preference ratings for infant faces that were normal, or were altered to appear normal. This supports the general hypothesis that adults are sensitive to, and biased against, cues of infant facial dysformities.

It is important to note that these appear to be unconscious biases, rather than deliberate biases. That makes them difficult to measure, and perhaps difficult to control. Nevertheless, we firmly believe that any such biases can be overcome by deliberate care and affection. Most importantly, Fetal Alcohol Syndrome is 100% preventable! To find out more about Fetal Alcohol Syndrome, please visit the Center for Disease Control.

With the help of Chinese-speaking research assistants, I have replicated much of our current findings with Caucasian participants and infants with Chinese participants and infants (2009). What this suggests is that infant facial cues are not specific to a particular culture. This in turn supports the idea that infant facial cues are a universal adaptation that are displayed by infants and perceived by adults in the same way across different cultures. Chinese men still valued cues of resemblance more than Chinese women, who most strongly valued cues of health and cuteness.

Infant and child faces change with age. But at what age do they have their greatest appeal? Certainly, cultural norms and values can influence the answer to this question. However, given the emphasis of evolutionary psychology on our understanding of child facial cues, it is reasonable to consider evolutionary hypotheses regarding child facial cues and age. There are three different hypotheses, each with their own limited support:

Youngest Is Best- this hypothesis states that children are most helpless and vulernable when young, and so their facial cues should be most affective at influencing adults when they are young.

Oldest Is Best- this hypothesis states that older children have surived the risky first couple of years of life (more 0-2 yr olds die than any other age category- this is especially true in cultures without modern medicine). Because older children have surived, they are likely to continue surviving and have shown that they were tough enough to survive that early period, so they must be of good quality.

Age Doesn’t Matter- this hypothesis states that either age cues don’t matter, or adults aren’t good at reading them.
To answer these questions, we ran two different studies with children of several different ages. You can see a video clip of a child aging here. Once again using the Hypothetical Adoption Paradigm, we found that adults were most interested in adopting younger children.

This graph shows a clear, significant, negative relationship between age and adoption preference. That is, adults prefer to adopt younger children. However, the obvious challenge is that adults prefer to adopt younger children not simply because their facial cues are more attractive/powerful, but because of socialization reasons (e.g., easier bonding). To answer this challenge, look at the shape of the cuteness relationship below.

This graph shows virtually the identical pattern as adoption preference. Cuteness shouldn’t be influence by the same social issues as adoption preference (e.g., easier bonding). So this shows that child facial cues appear to be stronger when younger, providing support for Hypothesis 1 above. These results were repeated in both experiments. The final question remaining is: do younger faces also appear healthier? That would be blending Hypotheses 1 & 2.

No, they do not. Younger faces are rated by adults to be less healthy-looking than older faces. This clinches the support for Hypothesis 1. Child facial cues are stronger when children are younger, presumably because when they are younger they are both more vulnerable to danger and in greater need of general assistance.

Interestingly, a later study we did on newborn infants showed that adults viewed them as less cute and worth adopting. From the infant’s perspective, this makes no sense as this is age when they need the most care and so should be sending the strongest signals. From the parents’ perspective however, this might be an adaptive response to prevent instant bonding in case the parent is stuck in conditions harsh enough to require reducing investment or even abandoning the infant (e.g., during a historic famine).