Depending on the species, bird eggs can be any color ranging from chicken's plain white to a robin's blue, streaked, spotted, bright, pale, and anything in between.

To find out, Hart and Risley embarked on an ambitious research project. They decided they would follow 40 families - rich, poor and in between - for the first three years of their children's lives.

Liquid crystals are considered to be intermediate between liquid and solid.