WHENEVER A BABY is born, there are always the inevitable discussions of which parent the baby resembles, whose ears he got, and where that nose came from. However, the father is usually the winner–babies are usually said to look most like the father, and even the mother will usually deny resemblance to herself in preference of the father. Why is this?

A mother invariably knows when a child is hers. She gestated the child, she delivered it, so her maternity is pretty much unassailable. But a father cannot be sure. It is possible that his partner cheated on him and her baby is actually the offspring of another man. Being cuckolded is a failing evolutionary strategy. If a male invests resources in raising offspring that does not belong to him, he loses the opportunity to produce his own offspring and existing offspring may pay a survival penalty due to lowered resources invested in them. Therefore evolution favors the development of strategies to detect paternity in offspring and fidelity in the mother.

Some of these methods are indirect and work by stacking the odds in the partner’s favor, such as monitoring of maternal activity and control of access to her by other males. However, males also use the physical appearance of offspring to attempt to determine paternity. A recent fMRI study showed that males demonstrate a different pattern of brain activity when viewing photographs of children than females do, with activity in the anterior cingulate gyrus.1 This area of the brain has been implicated in response inhibition and decision-making under uncertainty. The authors of this study think that the male brain checks images of children’s faces for self-resemblance, and when this is found inhibits suspicion of that child, possibly enabling enhanced paternal behavior.

Applying these findings to the current data, males may posses a generalized paternal uncertainty about children (Daly and Wilson, 1998; Platek et al., 2002, 2003) and this uncertainty may be inhibited when a child resembles him. Inhibition of scepticism, or uncertainty about a child’s paternity might produce appetitive paternal behavior toward children. Thus, the left medial frontal/ anterior cingulate activation associated with viewing self-child morphs may be an evolved response in males, which supports and extends the hypothesis put forth originally by Daly and Wilson (1982, 1998; see also Burch and Gallup, 2000; Platek et al., 2002, 2003; Regalski and Gaulin, 1993) that males use self-referent phenotype matching (i.e., resemblance; Lacy and Sherman, 1983) to assess paternity and make determinations about parental investment accordingly. Males also showed increased right parietal lobe and precuneus activation, which was active in main effect for resemblance contrast and in males for the child vs. adult contrast. These areas have also been associated with a network implicated in self-referent processing (Keenan et al., 2001; Platek et al., 2004a,b, under review). These findings may suggest that males activate a self-referent process when viewing children’s faces in an attempt to determine self-resemblance. Activation of anterior cingulate may coincide with positive decisions under uncertainty and increase paternal investment.

Since fathers screen putative offspring for self-resemblance, in this respect it is in a father’s best interest that his children look like him. Alleles contributing to paternity detection will be passed on as these males succeed in investing resources only in their offspring.

But let’s place the father in the position of cheater. If a male can impregnate a woman and trick her partner into raising the child instead of him, he wins all the way around. He produces more offspring, passes off the cost of raising these offspring onto an unsuspecting male, and retains more resources to raise his acknowledged children. In this respect it is in a father’s best interest that his children not look like him! Alleles suppressing paternal resemblance in infants will be passed on as these males succeed in foisting their offspring off onto unsuspecting males.

What about the baby? If she is indeed the daughter of her father, it would seem to be in her best interest to strongly resemble him, to advertise their relationship. But babies cannot control their mother’s actions nor determine when it is appropriate to look like daddy and when it is not. It is strongly in the baby’s best interest that her supposed father not realize one day, “Hey, baby looks like the mailman!” Overall, it’s in the baby’s best interest not to resemble the father. Once again, alleles suppressing paternal resemblance are more likely to succeed.

What about the mother? She can lose out twice. Both her genetic investment in her infant and her own wellbeing might be at risk if her baby’s paternity is in doubt. One study shows that mere perception of dissimilarity between a man and his offspring can contribute to family violence.2 If she is faithful it is in her best interest that her baby look like the father, but cheating is pretty common in our species (misattributed paternity is difficult to study but estimated conservatively at 1-5%, probably usually close to 2%3, but sometimes much higher), and in those cases it is in her best interest to have her baby not look like the father! There’s a way around this, though–if baby does not look like the father, but the mother can convince him that he does, things work out well in any scenario. Alleles favoring maternal reassurance of the partner’s paternity are passed on preferentially.

So we have alleles expressed in mothers and infants colluding to hide a baby’s paternity, while in fathers alleles for advertising paternity and alleles for hiding paternity are in conflict. Which wins? Typically it has been thought that increasing resemblance to the father is favored as the percentage of adulterine infants increases, reducing individual’s risk of harboring an unrelated infant.4 This does seem intuitively obvious. However, one model suggests that this is incorrect and selection overall favors anonymous infants.5 According to this model as the number of adulterine infants increases, it is more detrimental for males to discriminate based on offspring appearance because each male pays the penalty as his illegitimate children suffer, and in addition faces a danger of discriminating against his own children by mistake, further decreasing his reproductive effectiveness.

Then it is in the best interest of the father overall that his offspring not resemble him. Now I mentioned above that mothers will experience selection for heightened efforts to convince the father of infants’ resemblance to him, whether he is really the father or not. But is it in the father’s best interest to be skeptical of these claims lest he be deceived? Again, the model suggests the answer is no.

The expected reaction of fathers is interesting. One could think that they would be selected to resist their spouse’s manipulation. However, as long as their progeny are not identifiable, they will enjoy larger reproductive success when led to believe that the domestic offspring are their own. This is because, as shown by Eq. 2, the fitness of A-fathers [fathers producing anonymous offspring] increases when the cost of uncertainty s2 [parental reproductive cost of infant’s anonymity] decreases. If the whole argument holds, then, we should predict no consistent strategy of skepticism by fathers in the face of allegations of paternal resemblance. If it is in women’s genetic interest to increase paternity confidence by emphasizing baby’s resemblance to their mate, it is in men’s genetic interest to believe such claims.

So if the father can easily be convinced that his generic-looking baby belongs to him, the cost of producing generic-looking babies is decreased, and the reproductive success of fathers producing generic-looking babies is increased.

Equations are all very well, but how does this work out in the real world? Do babies really not look much like their dads? And do mothers really assert that they do? The answer to both of these questions is yes. A study of 160 couples with newborns tried to answer this by asking 60 couples together and 100 mothers alone which parent the baby resembled.6 When asked which parent their infant resembled, mothers with the father present replied 87.5% of the time that the baby looked like the father–but when the father was not in the room the paternal resemblance frequency suddenly dropped to 60.0%! Fathers reported self-resemblance only slightly more than half the time (51.4%). More than 1/3 of the time they gave no response since the mother apparently stepped in to answer first (the mother did not answer in only four cases). Unrelated judges matched the babies with their parents with success greater than chance, but were much more likely to match infants with their mothers, even when the father was the supposed best match.

So this evolutionary model explains quite well why mothers attribute paternal resemblance to their babies and why this resemblance is poor at best. Still to be answered is the question why all babies look like Winston Churchill.

  1. Platek, S. M.; Keenan, J. P.; Mohamed, F. B. Sex differences in the neural correlates of child facial resemblance: an event-related fMRI study.” NeuroImage 2005, 25, 1336-1344. DOI:10.1016/j.neuroimage.2004.12.037
  2. Burch, R. L.; Gallup, G. G. “Perceptions of paternal resemblance predict family violence.” Evolution and Human Behavior 2000, 21, 429-435. DOI:10.1016/S1090-5138(00)00056-8
  3. Anderson, K. G. “How Well Does Paternity Confidence Match Actual Paternity?: Evidence from Worldwide Nonpaternity Rates.” Current Anthropology 2006, 47, 513-518. DOI:10.1086/504167
  4. Johnstone, R. A. “Recognition and the evolution of distinctive signatures: when does it pay to reveal identity?” Proceedings of the Royal Society of London B 1997, 263, 1547-1553. DOI:10.1098/rspb.1997.0215
  5. Bressan, P. “Why babies look like their daddies: paternity uncertainty and the evolution of self-deception in evaluating family resemblance.” Acta Ethologica 2002, 4, 113-118. DOI:10.1007/s10211-001-0053-y
  6. McLain, D. K.; Setters, D.; Moulton, M. P.; Pratt, A. E. “Ascription of resemblance of newborns by parents and nonrelatives.” Evolution and Human Behavior 2000, 21, 11-23. DOI:10.1016/S1090-5138(99)00029-X