Lamarckism does not by itself explain adaptation

The Lamarckian theory - the inheritance of acquired characters - is not unscientific. Since Weissman, in the late nineteenth century, it has generally been accepted that acquired characters are not inherited.

Even if acquired characters were inherited, Lamarckism cannot account for adaptation in principle. The theory is unable to explain why an individual organism should respond adaptively to its environment: for instance, muscles, when exercised, grow stronger because of a pre-existing mechanism which is adaptive for the organism. The Lamarckian has no answer where that adaptive mechanism comes from, and for a complete explanation, it would have to fall back on another theory, such as God or natural selection. In the former case it would run into all the difficulties of natural theology and in the latter case it is natural selection, not Lamarckism, that is providing the fundamental explanation of adaptation.

Lamarckism could only work as a subsidiary mechanism; it could only bring adaptations into existence in so far as natural selection had already programmed the organism with a set of adaptive responses. Pure Lamarckism does not by itself explain adaptation.

The image opposite is of Jean Baptise Lamarck (1744-1829) who gave his name to the theory of acquired inheritance.