Do First Born Girls Look Like Their Fathers?

I recently met with a former close colleague to catch up and celebrate the birth of his first child. During a wide-ranging 4-hour (!) conversation, my friend dropped an intriguing nugget:

First born girls look more like their fathers than their mothers so their fathers are more likely to accept them, as historically men have preferred to have boys.

While my first reaction was to discard this idea entirely, I quickly found that some evolutionary psychologists have proposed that if babies looked like their fathers, it could boost the father’s confidence in paternity and increase his investment in the child, helping the baby survive and be more successful. In fact, there is some scientific evidence that when fathers perceive a child as looking like them (whether or not that’s objectively true), they report more emotional and financial investment. However, resemblance is ultimately subjective when children are young; people tend to see whichever parent they expect or want to see. Mothers are especially more likely to say the baby looks like the father, even when outside judges do not agree, but fathers are not particularly objective either.

Research that breaks down resemblance by child sex and age finds more complex patterns than first born girls looking like their fathers. For newborns, boys and girls resemble their mothers more than their fathers. Between 2 and 3 years of age, boys tend to resemble their fathers more while girls continue to resemble their mothers. However, this impact is no stronger for first born children than it is for all children.

Said another way, despite repeated claims in the popular press, there is no strong peer‑reviewed evidence that first born girls resemble fathers but later born girls do not. Instead, a form of confirmation bias is likely happening: humans are good at spotting family resemblance, fathers care about resemblance as a cue to paternity, and people notice and talk about cases where firstborns resemble fathers.

All of this combines to keep the story alive that first born girls look like their fathers – but they are no more likely to do so than any other kid.