(HealthDayNews) -- Twins may look alike to people who don't know them -- but to their parents, they're always very different.
In fact, according to the Italian-language journal Acta Geneticae Medicae Et Gemellologiae, mothers sometimes show a preference for one twin, and fathers for the other.
Researchers at the University of Oulu in Finland studied 234 pairs of twins, from birth to age 21.
Mother's favorite twin was more likely to be the first one to speak, and was usually the smarter of the two. But the same twin more often had sleeping difficulties and some psychosomatic symptoms in adolescence.
Father's favorite was more likely to be physically oriented and less accident prone. This twin was also likely to insist that the pair should dress differently, and that the siblings should not always be together.
