On the Origin of Species Darwin's ideas with those of Lamarck and Goethe while still reflecting the spirit of "Naturphilosophie". Their ambitious programme to reconstruct the evolutionary history of life was joined by Huxley and supported by discoveries in palaeontology. Haeckel used embryology extensively in his recapitulation theory, which embodied a progressive, almost linear model of evolution. Darwin was cautious about such histories, and had already noted that von Baer's laws of embryology supported his idea of complex branching. Asa Gray promoted and defended "Origin" against those American naturalists with an idealist approach, notably Louis Agassiz who viewed every species as a distinct fixed unit
Reactions to On the Origin of Species breeding that would eventually form part of "The Variation of Animals and Plants under Domestication". He wrote to Asa Gray and used the example of fantail pigeons to argue against Gray's belief "that variation has been led along certain beneficial lines", with the implication of Creationism rather than Natural Selection. Over the winter he organised a third edition of the "Origin", adding an introductory historical sketch. Asa Gray had published three supportive articles in the "Atlantic Monthly". Darwin persuaded Gray to publish them as a pamphlet, and was delighted when Gray came up with the title of "Natural Selection Not