How is Darwin's theory different to other theories

Darwin's theory said that there are variations within a population, the ones with advantages will have a better chance of survival and therefore reproduce. (natural selection) after a period of time that advantage will become more abundant

whereas lamarck's said that all individuals within a population was the same, the more the species used a feature, the more it became abundant

eg.. GIRAFFES,

darwin: there are ones with long necks and there are ones with short necks, the long necks are able to get food so the short ones died off, over time long necks became common

others: the giraffes needed to stretch their necks to get to food higher up so over time long necks became more common

:) hope tht helped

It proposed a credible mechanism by which evolution could occur, which was natural selection.

Edit:
By "theories" I'm assuming you're talking about other theories proposed about how organisms change over time, such as by Lamarck.