Half the genes, but not half the face
Every child inherits two versions of each gene, one from each biological parent. So your baby's genes come half from each of you, yet their looks rarely split down the middle. There are three reasons.
First, when the two versions of a gene differ, often only one of them shows. The other is masked, so a child can carry something from one parent that nobody can see.
Second, many features depend on lots of genes at once. Hair colour, for example, is set by many genes, and little is known about most of them. With so many genes in play, the overall mix can lean towards one side of the family.
Third, each parent has two versions of each gene and passes on only one, so every child gets a different mix, and brothers and sisters can take after different sides.
The study that said babies look like their fathers
In 1995, Nicholas Christenfeld and Emily Hill of the University of California, San Diego, published a short report in Nature called "Whose baby are you?". Volunteers saw a photo of a child above photos of three adults, one of them the child's parent, and tried to pick the parent. The photos came from 24 families.
The report found that 1-year-olds resembled their fathers more than their mothers. It received a lot of attention, both in science and in the popular press.
Even in that study, the effect was modest. Fathers were picked correctly from a baby's photo in about 49% of cases, against 33% by pure guesswork. The study also compared each parent to guesswork rather than comparing mothers and fathers directly.
What later studies found
In 1999, Serge Brédart and Robert French at the University of Liège in Belgium repeated the experiment with 28 families, using photos of the same child at 1, 3 and 5 years old. In all, 180 students took part. At every age, they picked out mothers and fathers about equally well, with no significant difference between them. Both were found more often than by chance, but not by much: in every condition, people chose the wrong adult more than half the time. The authors concluded that the original result was most likely incorrect.
In 2007, a team led by Alexandra Alvergne looked at children from birth to 6 years old, again using photos rated by judges unrelated to the families. Children resembled both parents more than chance at every age. Newborns, both boys and girls, resembled their mothers more. Girls kept that pattern, while boys switched to resembling their fathers more at around 2 to 3 years.
So there is no reliable rule that babies look like one parent. The most consistent finding is that resemblance is real but subtle, and that strangers are not very good at spotting it.
These studies looked at families with a mother and a father, but the genetics is the same for every couple: each biological parent passes on one version of each gene.
Why everyone says the baby looks like the father
If you have heard "the baby looks just like the father" more than once, you are not alone. In 1982, Martin Daly and Margo Wilson studied what people say about newborns. They recorded mothers just after the birth and used questionnaires filled in by mothers, fathers and relatives on both sides. A likeness to the father was claimed far more often than a likeness to the mother, although many fathers were sceptical.
The 2007 study by Alvergne's team saw the same thing: at birth, mothers said the baby resembled the father, while the outside judges found the opposite. What families say and what a face shows are two different things.
Resemblance changes as they grow
A newborn's face is a first draft. The studies above suggest that who a child resembles most can shift in the first few years, at least for boys. Colouring changes too. Particularly in people of European descent, light hair may darken with age, and blond-haired children often have darker hair by the time they are teenagers.
So if your baby looks like one of you at first, that may not last.
If you want to know the odds for a single feature, our free tools work from what each of you looks like: the eye colour calculator, the hair colour calculator and the child height predictor.
Imagine it, for fun
You do not have to wait to start guessing. The AI baby photo generator blends a photo of each of you into an imagined child, so you can see a face that mixes both of you. It is a fun picture to share, not a forecast: no photo can show which versions of your genes your baby will actually inherit.