[Wallace's] concept of lineage-adaptation as a sequence of extinctions of less fit and survival of fitter varieties and his gradualism put him closer to Darwin than to Matthew. But he emphasized environmental changes for differential extinction and some form of isolation for lineage-splitting and speciation, whereas Darwin's mature theory saw competition as a sufficient cause of divergence, differential extinction, lineage-adaptation and lineage-splitting. This is not to say that Darwin was right in this view and Wallace wrong. By current standards, they were both right and wrong in different respects (competitive vs. environmental selection, sympatric vs. allopatric speciation).