Dr. Turner is studying shyness. He finds that Blake and Luke, identical twins, are more alike in terms of level of inhibition than are Sam and Carl, who are fraternal twins. His research indicates that ______ plays an important role in shyness.
In fraternal twins, two eggs are fertilized at once rather than just one egg. This means that a woman releases two eggs and this is not caused by the father's genes because a man cannot make a woman produce and release two eggs. This implies that fraternal twins may be hereditary. Hence comparing the level of shyness in identical and nonidentical twin is more like comparing the impact of heredity on inhibition levels.
