Your friend Alex and Katya are concerned that their 9-month-old daughter Mariana often uses her left hand to pick up objects. Alex and Katya are both right-handed, and they do not want Mariana to be left-handed because it is a right-handed world

What can you tell your friends about the roles of heredity and environment in the development of hand preference?
What will be an ideal response?

A good answer will be similar to the following:
Most 6- to 9-month-olds use their left and right hands equally so it is unlikely that Mariana's use of her left hand now will predict her later hand preference. By 13 months, most children start to show a preference for one hand over the other. Throughout the preschool years, preference for one hand becomes stronger and more consistent so that by the time the child enters kindergarten hand preference is well established. Heredity does influence handedness. Most left-handed people have a parent or grandparent that was left-handed. Given that both Alex and Katya are right-handed, it is less likely that they have genes for left-handedness to pass along. Experience also plays a role in the development of hand preference. For example, in some countries left-handedness is viewed as evil traditionally and children have been punished for using their left hand to eat or write. Given that Mariana has two right-handed parents who are likely to encourage right-handed behavior, she will probably become right-handed, but it is too early to tell.