(COSMOPOLITAN) January 2007:

There’s no conclusive hard data, but some experts believe that many babies resemble their dads in infancy to prove paternity and encourage the father to bond with the child.  “Dads are left out of the pregnancy process, so seeing features that look like theirs brings out their caretaking instinct,” says Nicholas Christenfeld, PhD., professor of psychology at the University of California at San Diego.