254 I The Process of Evolution 



described as a fossil. It was not until some 5 years after its descrip- 

 tion from leaf impressions in Pliocene deposits in Japan that living 

 plants were found growing in China. Again, this tree apparently 

 has been preserved from extinction at least in part through culti- 

 vation by the Chinese. 



In addition to such instances of completely isolated species, there 

 are also cases of two or only a few closely related forms which, as a 

 group, are clearly separated from their nearest living relatives. In 

 the butterfly genus Neophasia (Pieridae) are found what are con- 

 sidered by all lepidopterists to be two distinct species with no 

 intermediates and little intraspecific variation. One species, N. 

 menapia, is widespread in western North America, where it feeds on 

 various coniferous trees. Both sexes are white, with black markings 

 restricted largely to the leading edge and apex of the forewings. 

 Neophasia terlooti is found in northern Mexico and Arizona; it also 

 feeds on conifers. Males are similar to those of N. menapia, but the 

 dark markings on the forewings are more extensive. The females 

 resemble the males, except that the white ground color has been 

 replaced by orange-red. No red females of N. menapia are known, 

 and no white females of IV. terlooti are found. 



Living elephants are an interesting example of two very distinct 

 species as the only survivors of a diversified group. Thus the African 

 elephant (Loxodonta ofricana) clearly is the closest living relative 

 of the Indian elephant (Elephas maximus) and vice versa. Both, 

 however, have closer relatives among known extinct forms not di- 

 rectly ancestral to them. 



Detailed studies of the closed-cone pines of western North Amer- 

 ica have revealed a similar situation among these plants. Pinus 

 masoni is known only from the Pliocene. From study of the abundant 

 fossils, it has been suggested that P. masoni became extinct in the 

 Pleistocene after giving rise to two separate lines of development. 

 One of these produced P. linguiformis, which also became extinct in 

 the Pleistocene. From P. linguiformis arose P. attenuata, which has 

 a fossil record extending well back into the Pleistocene and which 

 is today the commonest species of closed-cone pine in California. 

 The second phyletic line deriving from P. masoni gave rise to P. 

 muricata. This species survives today and is abundant along the 

 Pacific Coast, together with its derivatives P. radiata and P. re- 

 morata. If only modern pines are considered, P. attenuata and P. 

 muricata are obviously closely related morphologically. Both, how- 

 ever, have close relatives in the fossil forms that preceded and 

 overlapped them in time, only to become extinct during the Pleisto- 

 cene. These two pines appear to be vigorous expanding species with 



