In this essay, we will look into the existing body of criticisms which have been brought against the modern theory of evolution; we will investigate the nature and extent of these criticisms and con­ clude with an evaluation of their meanings and significance and the possible impact they will have on the future development of the theory. Before we proceed to identify the above body of criticisms, we need to clarify the meaning of the precise idea or concept that is being criticized since the term evolution has been used to convey dif­ ferent meanings and connotations. Herbert Spencer, for example, who is considered the first great evolutionist and who gave the word evolution its modern connotation in English, used the word in two different senses in his essay The Development Hypothesis 1 which appeared in the Leader between 1851 and 1854, that is several years before the publication of Darwin's The Origin of Species. In this essay as well as in his later work The Principles of Biology, Spencer describes both the development of an individual adult organism from a mere egg and phylogenetic transformation of species as processes of evo­ lution. 2 This usage of a single term, namely evolution, to describe two altogether fundamentally different processes has generally been avoided by today's scientists. But the possibility of confusion 1 This essay was reprinted in Essays: Scientific, Political and Speculative (London, 1868). In it Spencer asks why people find it so very difficult to suppose "that by any series of changes a protozoon should ever become a mammal" while an equally wonderful process of evolution, the development of an adult organism from a mere egg, stares them in the face.