274 BIOLOGY: GENERAL AND MEDICAL 



changes of function also modify or create new organs. By 

 changes of environment animals become subjected to new sur- 

 roundings, involving new ways and means of living. Thus, certain 

 land birds, driven by necessity to obtain their food in the water, 

 gradually assumed characters or structures adapting them for 

 swimming, wading, or for searching for food in the shallow water, 

 as in the case of the long-necked kinds. 



3. "Use and disuse. To use an organ is to develop it; not to 

 use it is to eventually lose it. The anterior limbs of birds became 

 capable of sustained flight through use; the hind limbs of whales 

 are lost through disuse, etc. 



4. "Competition. Nature takes precautions not to overcrowd 

 the earth. The stronger and larger living things destroy and 

 devour the smaller and weaker. The smaller multiply very 

 rapidly, the larger slowly. A physiological balance is maintained. 



5. "The transmission of acquired characters. The advantage 

 gained by every individual as the result of the structural changes 

 resulting from use or disuse are handed down to its descendants 

 who begin where the parent leaves off, and so are able to continue 

 the progression or retrogression of the character. 



6. "Cross-breeding. 'If when any peculiarities of form or any 

 defects whatsoever are acquired, the individuals in this case 

 always pairing, they will produce the same peculiarities, and if for 

 successive generations confined to such unions, a special and 

 distinct race will then be formed. But perpetual crosses between 

 individuals which have not the same peculiarities of form result 

 in the disappearance of all the peculiarities acquired by the 

 particular circumstances.' 



7. "Isolation. 'Were not men separated by distances of 

 habitation, the mixtures resulting from crossing would obliterate 

 the general characters which distinguish different nations/ This 

 thought is expressed in his account of the origin of man from apes, 

 and is not applied to living things in general." 



Lamarck sums up his ideas in four laws published in 

 his " Animaux sans Vertebres," 1815: 



I. "Life, by its proper forces, continually tends to increase 

 the volume of every body which possesses it, and to increase the 

 size of its parts, up to a limit which brings it about." 



II. "The production of a new organ in the animal body results 

 from the supervention of a new want which continues to make 

 itself felt, and of a new movement which this want gives rise to 

 and maintains." 



III. "The development of organs and their power of action 

 are constantly in ratio to the employment of these organs." 



IV. " Everything which has been acquired, impressed upon, or 

 changed in the organization of individuals during the course of 

 their life is preserved by generation and transmitted to new 

 individuals which have descended from those which have under- 

 gone those changes." 



