حبّةٌ واحدة في الميزان تقرّر أيّ فرد يحيا وأيّ فرد يموت، وأيّ نوعٍ أو سلالةٍ تزداد أعدادها، وأيّها تتناقص، أو تنقرض في النهاية.

“A grain in the balance will determine which individual shall live and which shall die - which variety or species shall increase in number, and which shall decrease, or finally become extinct.”Charles Darwin — On the Origin of Species: By Means of Natural Selection Or the Preservation of Favored Races in the Struggle for Life (2007)