darwin and modern science-第52章
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causal connection between ontogeny and phylogeny。 〃Phylogenesis is the mechanical cause of ontogenesis〃； in other words； 〃The evolution of the stem or race isin accordance with the laws of heredity and adaptationthe real cause of all the changes that appear； in a condensed form； in the development of the individual organism from the ovum； in either the embryo or the larva。〃
It is now fifty years since Charles Darwin pointed out； in the thirteenth chapter of his epoch…making 〃Origin of Species〃； the fundamental importance of embryology in connection with his theory of descent：
〃The leading facts in embryology； which are second to none in importance； are explained on the principle of variations in the many descendants from some one ancient progenitor； having appeared at a not very early period of life； and having been inherited at a corresponding period。〃 （〃Origin of Species〃 （6th edition）； page 396。）
He then shows that the striking resemblance of the embryos and larvae of closely related animals； which in the mature stage belong to widely different species and genera； can only be explained by their descent from a common progenitor。 Fritz Muller made a closer study of these important phenomena in the instructive instance of the Crustacean larva； as given in his able work 〃Fur Darwin〃 （1864）。 （English translation； 〃Facts and Arguments for Darwin〃； London； 1869。） I then； in 1872； extended the range so as to include all animals （with the exception of the unicellular Protozoa） and showed； by means of the theory of the Gastraea； that all multicellular； tissue…forming animalsall the Metazoadevelop in essentially the same way from the primary germ…layers。 I conceived the embryonic form； in which the whole structure consists of only two layers of cells； and is known as the gastrula； to be the ontogenetic recapitulation； maintained by tenacious heredity； of a primitive common progenitor of all the Metazoa； the Gastraea。 At a later date （1895） Monticelli discovered that this conjectural ancestral form is still preserved in certain primitive CoelenterataPemmatodiscus； Kunstleria； and the nearly…related Orthonectida。
The general application of the biogenetic law to all classes of animals and plants has been proved in my 〃Systematische Phylogenie〃。 （3 volumes； Berlin； 1894…96。） It has； however； been frequently challenged； both by botanists and zoologists； chiefly owing to the fact that many have failed to distinguish its two essential elements； palingenesis and cenogenesis。 As early as 1874 I had emphasised； in the first chapter of my 〃Evolution of Man〃； the importance of discriminating carefully between these two sets of phenomena：
〃In the evolutionary appreciation of the facts of embryology we must take particular care to distinguish sharply and clearly between the primary； palingenetic evolutionary processes and the secondary； cenogenetic processes。 The palingenetic phenomena； or embryonic RECAPITULATIONS； are due to heredity； to the transmission of characters from one generation to another。 They enable us to draw direct inferences in regard to corresponding structures in the development of the species （e。g。 the chorda or the branchial arches in all vertebrate embryos）。 The cenogenetic phenomena； on the other hand； or the embryonic VARIATIONS； cannot be traced to inheritance from a mature ancestor； but are due to the adaptation of the embryo or the larva to certain conditions of its individual development （e。g。 the amnion； the allantois； and the vitelline arteries in the embryos of the higher vertebrates）。 These cenogenetic phenomena are later additions； we must not infer from them that there were corresponding processes in the ancestral history； and hence they are apt to mislead。〃
The fundamental importance of these facts of comparative anatomy； atavism； and the rudimentary organs； was pointed out by Darwin in the first part of his classic work； 〃The Descent of Man and Selection in Relation to Sex〃 （1871）。 （〃Descent of Man〃 （Popular Edition）； page 927。） In the 〃General summary and conclusion〃 （chapter XXI。） he was able to say； with perfect justice： 〃He who is not content to look； like a savage； at the phenomena of nature as disconnected； cannot any longer believe that man is the work of a separate act of creation。 He will be forced to admit that the close resemblance of the embryo of man to that； for instance； of a dogthe construction of his skull； limbs； and whole frame on the same plan with that of other mammals； independently of the uses to which the parts may be putthe occasional reappearance of various structures； for instance of several muscles； which man does not normally possess； but which are common to the Quadrumanaand a crowd of analogous factsall point in the plainest manner to the conclusion that man is the co…descendant with other mammals of a common progenitor。〃
These few lines of Darwin's have a greater scientific value than hundreds of those so…called 〃anthropological treatises；〃 which give detailed descriptions of single organs； or mathematical tables with series of numbers and what are claimed to be 〃exact analyses；〃 but are devoid of synoptic conclusions and a philosophical spirit。
Charles Darwin is not generally recognised as a great anthropologist； nor does the school of modern anthropologists regard him as a leading authority。 In Germany； especially； the great majority of the members of the anthropological societies took up an attitude of hostility to him from the very beginning of the controversy in 1860。 〃The Descent of Man〃 was not merely rejected； but even the discussion of it was forbidden on the ground that it was 〃unscientific。〃
The centre of this inveterate hostility for thirty yearsespecially after 1877was Rudolph Virchow of Berlin； the leading investigator in pathological anatomy； who did so much for the reform of medicine by his establishment of cellular pathology in 1858。 As a prominent representative of 〃exact〃 or 〃descriptive〃 anthropology； and lacking a broad equipment in comparative anatomy and ontogeny； he was unable to accept the theory of descent。 In earlier years； and especially during his splendid period of activity at Wurzburg （1848…1856）； he had been a consistent free…thinker； and had in a number of able articles （collected in his 〃Gesammelte Abhandlungen〃） （〃Gesammelte Abhandlungen zur wissenschaftlichen Medizin〃； Berlin； 1856。） upheld the unity of human nature； the inseparability of body and spirit。 In later years at Berlin； where he was more occupied with political work and sociology （especially after 1866）； he abandoned the positive monistic position for one of agnosticism and scepticism； and made concessions to the dualistic dogma of a spiritual world apart from the material frame。
In the course of a Scientific Congress at Munich in 1877 the conflict of these antithetic views of nature came into sharp relief。 At this memorable Congress I had undertaken to deliver the first address （September 18th） on the subject of 〃Modern evolution in relation to the whole of science。〃 I maintained that Darwin's theory not only solved the great problem of the origin of species； but that its implications； especially in regard to the nature of man； threw considerable light on the whole of science； and on anthropology in particular。 The discovery of the real origin of man by evolution from a long series of mammal ancestors threw light on his place in nature in every aspect； as Huxley had already shown in his excellent lectures of 1863。 Just as all the organs and tissues of the human body had originated from those of the nearest related mammals； certain ape…like forms； so we were bound to conclude that his mental qualities also had been derived from those of his extinct primate ancestor。
This monistic view of the origin and nature of man； which is now admitted by nearly all who have the requisite acquaintance with biology； and approach the subject without prejudice； encountered a sharp opposition at that time。 The opposition found its strongest expression in an address that Virchow delivered at Munich four days afterwards （September 22nd）； on 〃The freedom of science in the modern State。〃 He spoke of the theory of evolution as an unproved hypothesis； and
