AN EMBRYOLOGIST'S VIEW OF 

 THE SPECIES CONCEPT 



JOHN A. MOORE: departments of zoology, barnard 



COLLEGE AND COLUMBIA UNIVERSITY, NEW YORK 



Nature never made species mutually sterile 

 by selection, nor will men. — Darwin to T. H. 

 Huxley, Jan. 7, 1867, in More Letters, vol. 1, 

 p. 277, Letter 197. 



If an embryologist is asked to contribute his views to a sympo- 

 sium on "The Species Concept" it could be for any of several 

 reasons, such as his interest in the origin of things, in this case 

 species, or the possibility that information on gametes and early 

 embryos can aid our understanding of this taxonomic category. 



The data that I will present have a bearing on the origin of 

 species and on the complex intergroup and intragroup relations 

 in natural populations. Most of these data have appeared pre- 

 viously (Moore, 1946, 1947, 1949a,b, 1950, 1954, 1955) but they 

 have not been used for the specific problem of this symposium. 



Current Views on the Origin of Species 



The work of systematists in the last part of the nineteenth cen- 

 tury and in the twentieth century has made a strong case that one 

 pattern of speciation involves divergence in geographically iso- 

 lated populations. The assumed events may be outlined in a 

 simple fashion as follows: A single species becomes distributed 

 over a large area, which is divided by barriers into a number of 

 smaller areas. The barriers are such that gene exchange between 

 the populations of the geographically isolated areas is greatly 

 reduced or almost absent. With the passage of time each popula- 

 tion evolves in an essentially different phyletic line. The course 

 of these separate evolutions is assumed to involve the selection 



325 



