Babies' cuteness is a powerful force to be reckoned with. It melts adult hearts, ensuring babies a steady source of food and protection until they mature to an age when they're slightly less vulnerable.

What is it about babies that makes them so cute? It's their eyes, which are huge relative to their faces (eyeballs don't grow all that much after birth); their heads, which are too big for their bodies; their cheeks; and their tiny chins that get adults to fixate on them.

Scientists say these traits activate an instinctual attention in adults. Brain scan studies have found evidence of an immediate reaction to babies in parents and non-parents alike in the orbitofrontal cortex, a region of the brain thought to be involved in rewarding and decision-making. Cute babies are just extremely hard to ignore, and this is likely hardwired into our brains.

How we react to less attractive babies

There's some evidence to suggest that less cute children are treated differently. A review of the scientific literature in the journal Trends in Cognitive Sciences highlights a few conclusions that point in this direction.

The first: "Both men and women will expend extra effort to look longer at cute infant faces."

So cuter babies command more attention. Does this mean adults prefer them? "When presented with cute and less-cute infants, adults prefer to give a toy to, or even adopt, the cuter one," they write.

The problem of cuteness discrimination is more acute when the baby has a physical abnormality. Brain scans show that adults — who usually have immediate brain activity when gazing on an infant's face — will show less activity when babies have a "craniofacial abnormality that disrupts the typical cute facial composition."

In the real world, this plays out with tragic consequences. Babies with cleft lips and palates are more likely to have "adverse outcomes in child development, including cognitive problems," the paper writes. "These problems can at least partly be attributed to early disruptions in mother-child interactions, specifically a lack of all-important maternal responsiveness." The implication is that the mother is less responsive because the child is less cute.

There's more to cuteness than the face

There's some hope for babies who are less attractive than their peers. The authors of the review in Trends in Cognitive Sciences make the case that there other, nonfacial, components to cuteness: "sight, sound, or smell of infants can help facilitate caregiving and perhaps promote other sophisticated emotional behaviors," they write. (Also all parents have a bias to see the cuteness in their own children.)

What's also true is this: No baby can stay cute forever. "Both adults and children pay more attention to infants' faces than to older children's faces," the authors write, "suggesting the power of cuteness in young children's faces fades as children mature."

And however unsightly a child might be, it's unlikely that one would be so hideous as to provoke reactions like Elaine Benes and Jerry Seinfeld's here:

Why babies in medieval paintings look like ugly old men