Identical twins are a perfect test case for theories of personality development. If a theo

ry can't explain the differences between identical twins, then it cannot explain environmental effects on personality. Even identical twins brought up in the same home have different personalities.

Take Ladan and Laleh Bijani from Iran. They were identical twins who had spent their entire 29 years joined at the head. And yet, Ladan, the more outspoken of the pair, told journalists, "We are two completely separate individuals, we have different world views, We have different lifestyles, we think very differently about issues." Why did Ladan and Laleh have different personalities？

Self-organized systems in insects can provide us with some ideas. A colony of ants, for example, can be seen as a self-organized system. No supervisor tells the ants what to do, and yet all the jobs get done. The system works in such a way that if one ant carries out a particular job, it be comes less likely that another ant will attempt that job because it no longer needs doing. The result is what economists call "division of labor. "

Self-organization also produces division of labor in human groups. Each individual looks for something to specialize in, his or her own suitable position in the group. If one position is occupied, the individual will seek another. This process increases the differences even between identical twins, because once they've chosen different specialities, a circular mechanism causes small initial differences between them to widen.

Although identical twins look very much alike, people who know them well will distinguish between them. They might, for example, address more questions and comments to one twin than the other—perhaps by chance first. But the consequence is that the twin who is addressed more of ten will do more talking than the other twin, which will cause people who know them to address still more of their questions and comments to that twin. The result, over time, will be one outspoken twin and one quieter one—like Ladan and Laleh Bijani.

According to the writer we learn that identical twins______.

A．differ in personality

B．differ in appearance

C．have the same lifestyle

D．have the same outlook