Missing Links 



species, since these must have been spread over 

 so many ages, and have existed in such numbers, 

 that it seems impossible to account for their total 

 absence from deposits in which great numbers of 

 species belonging to other groups are preserved 

 and have been discovered." 



Wallace's reply is to the effect that in the case 

 of many species palaeontology affords abundant 

 evidence of the gradual change of one species into 

 another, the foot of the horse being a well-known 

 case. The genealogy of this noble quadruped 

 can be traced from the Eocene four- toed Orohip- 

 pus, through the Mesohippus, the Miohippus, the 

 Protohippus, and the Pliohippus, until we reach 

 the one-toed Equus. 



Wallace further points out that in order that 

 the fossil of any organism may be preserved, the 

 " concurrence of a number of favourable condi- 

 tions " is required, and against this the chances 

 are enormous. Lastly, he urges the imperfection 

 of our knowledge of the things that lie embedded 

 in the earth's crust. 



The objection based on the lack of " missing 

 links " loses some of its force if we accept the 

 theory that species sometimes arise as sports. 

 Thus, suppose a species with well-developed 

 horns produces as a mutation a hornless variety, 

 which eventually replaces the horned form, we 

 should look in vain for any forms intermediate 

 between the parent and the daughter species. 



41 



