This article examines W. K. C. Guthrie΄s suggestion that Aristotle΄s doctrine of substantial form (eidos) no longer has value, since "it makes Darwinian evolution impossible". While it is true that in his biological writings Aristotle excludes the evolution of species, I suggest that his metaphysics is eminently receptive to the theory should the facts support it. He elucidates, moreover, basic philosophical questions, which must be confronted by any theory of evolution. Doctrines that are fundamental for a theoretical consideration of evolution are his concepts of act and potency, form and finality, the nature of causation and the explanation of chance. Questions raised by evolution to which Aristotle΄s metaphysics, however, is unable to respond include the ultimate significance of finality and the question of existence itself. Eidos is for Aristotle the deepest principle of individual substance. Form is inseparable from finality; individuals are properly realised and defined in the completed actuality of their nature: physis is both origin and end. Since Aristotle΄s notion of telos does not imply intelligence, his theory is best described by the recent term «teleonomy», rather than «teleology». The notion of substantial form, dominant in ancient and medieval philosophy, was rejected by modern thinkers. Darwin also sought to reduce structure to the conditions from which it arose, rather than acknowledge it as structure in itself; hence the suggested incompatibility with Aristotle. It may be argued that the question of form is prior to the debate concerning the origin of species. Aristotle΄s denial of evolution in his biological writings does not invalidate, a priori, his fundamental insight into form as metaphysical principle. Form is required in order to account for the basic taxonomy of the natural world, and to distinguish the living from non-living. Material causality is insufficient to explain the irreducible complexity of life; biology may not be reduced to mechanics. Aristotle anticipates certain aspects of evolutionary theory, such as the gradation of species and the dualising nature of the ape. He rejected pangenesis - the theory that the individual is entirely formed from the start - in favour of epigenesis, according to which it grows and develops gradually, actualising latent potencies. Analogously, his notion of form may be extended prospectively to embrace its dormant potencies. Contemporary scholars recognise in Aristotle΄s genetics an anticipation of the principle of DNA, the single most important factor in evolutionary biology. With certain adaptations, a theory of evolution may be accommodated to a modified metaphysics of Aristotle. (An extended treatment of this theme appears in The Review of Metaphysics, 2004).