Who among the following implied natural selection as a mechanism of evolution?

Alfred Wallace implied that natural selection is a mechanism of evolution.The fitness, according to Darwin, refers ultimately and only to reproductive fitness. Hence, those who are better fit in an environment, leave more progeny than others. These, therefore, will survive more and hence are selected by nature. Darwin called it natural selection and implied it as a mechanism of evolution. Alfred Wallace, a naturalist who worked in Malay Archipelago had also come to similar conclusions around the same time.