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.
In modern usage science most often refers to a way of pursuing knowledge, not only the knowledge itself. In the 17th and 18th centuries scientists increasingly sought to formulate knowledge in terms of laws of nature.his means a scientist would not ask merely What is the cause of ..., but rather What are the most significant causes of .... This is especially the case in the more macroscopic fields of science (e.g. psychology, cosmology).