In science, the meaning of "theory" is different than the one we use commonly.
In the day-to-day, "theory" means a supposition or speculation, while a scientific theory is an explanation of a certain aspect of nature that is supported by evidence collected from several sources, and that has been tested repeatedly following the scientific method. A scientific theory is considered to be a truth, which is the case for natural selection and evolution.
i use alot when i f my girlfriend. i'm doing her in the bathroom at summer school. shes getting her tight jeans off and then we'll begin