IO DARWINISM AND EVOLUTION. 



" excessively hairy leaves ; in wet seasons .white petals and smooth 

 " leaves ; in fact, the leaves of the whole plant vary from an eighth 

 " of an inch to more than an inch in length. AH tlie roses 

 "growing wild in Caithness may have come from one stock, but 

 " from what particular stock I cannot tell." 



As regards animals, a careful series of observations has lately 

 been made in America, with the result of ascertaining that in wild 

 individuals the amount of measurable variation — length, circum- 

 ference, weight — is to the extent of between 10 per cent, and 20 

 per cent, of the average dimensions. 



3. Individual peculiarities are transmissible to offspring. As 

 witness to the truth of this proposition, we may refer to all 

 gardeners, pigeon fanciers, and breeders of cattle. All the homes 

 in England present family likenesses, and inherited mental endow- 

 ments and moral traits. A mare crossed with a quagga has a 

 striped foal. It is well known that some diseases are hereditary ; 

 and rabbits in whom epilepsy has been artificially induced, have 

 epileptic progeny. 



4. Individuals whose peculiarities bring them into closest 

 adaptation with their environment are those which survive and 

 transmit their peculiar organisations. One's environment is the 

 circumstances in which one is placed. Friends, foes, food, 

 climate, temperature, and the constitution of the atmosphere ; all 

 things that can act upon us, and upon which we can re-act, form 

 our environment. Plants that can best protect themselves from 

 the depredations of insects, will outlive others. The swallow, 

 strong in flight, will reach the promised land, when weak ones 

 perish in the wilderness. In every migration the feeble flyers are 

 weeded out, and the strong survive and multiply. In a close 

 commercial competition, men with clear heads and sober habits, 

 with untiring energies and enduring frames, are more closely than 

 others adapted to their environment, will win in life's race, will 

 survive and transmit their peculiar organisations. 



5. The survival of the fittest thus tends to maintain an equi- 

 librium between organisms and their environments. No two cubs 

 of a polar bear are covered with exactly the same quantity of fur. 

 If the fur of one of them is insufficient to protect him from the 

 arctic cold, he will perish. If the fur of another is so thick as to 

 hinder his hunting for food, he will be at a disadvantage. The 

 fittest to survive will be in equilibrium with his environment. 



6. But the environment of every group of organisms is steadily, 

 though slowly, changing. The intensity of the sun's heat varies. 

 Local temperature is affected by the precession of the equinoxes. 

 Periodic changes take place in the shape of the earth's orbit. 

 Glacial epochs come and go. The surface of the earth rises and 

 falls. Islands are joined into continents ; and continents are 

 broken up into islands. Food is plentiful or disappears in a 



