Our masters taught: There are three partners in man -- G-d, his father, and his mother. His father inseminates the white substance, out of which are formed the child's bones, sinews, and nails, the brain in his head, and the white of his eye. His mother inseminates the red substance, out of which are formed the child's skin, flesh, and hair, and the black of his eye. G-d implants in him spirit, soul, beauty of countenance, eyesight, the capacity to hear, the capacity to...
Talmud, Niddah 31a