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
On the Origin of Species disperse across oceans to colonise distant islands. By 1856, his theory was much more sophisticated, with a mass of supporting evidence. In his autobiography, Darwin said he had "gained much by my delay in publishing from about 1839, when the theory was clearly conceived, to 1859; and I lost nothing by it". On the first page of his 1859 book he noted that, having begun work on the topic in 1837, he had drawn up "some short notes" after five years, had enlarged these into a sketch in 1844, and "from that period to the present day I have steadily