Being the only child is a unique position in a family. Without any siblings to compete with, the only child monopolizes his parents' attention and resources, not just for a short period of time like a firstborn, but forever.
Like gravity and plate tectonics, evolution is a scientific theory. In science, a theory is the most logical explanation for how a natural phenomenon works. It is well tested and supported by abundant evidence. It means quite the opposite from our informal use of the word theory, which implies an untested opinion or guess. As a scientific theory, evolution enables scientists to make predictions and drives investigations that lead to new kinds of observable evidence.
science noun [C/U]. âº the âsystematic âstudy of the âstructure and âbehavior of the ânatural and âphysical âworld, or âknowledge âobtained about the âworld by âwatching it âcarefully and experimenting: [U] Advances in âmedical science âmean that âpeople are âliving âlonger. [U] She âshows a âtalent for âmath and science.