20 READINGS IN EVOLUTION, GENETICS, AND EUGENICS 
may lead to the origination or modification of organs; that changes 
of function also modify or create new organs. By changes of environ- 
ment animals become subjected to new surroundings, involving new 
ways and means of living. Thus, certain land birds, driven by neces- 
sity to obtain their food in the water, gradually assumed characters 
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 the smaller 
and weaker. The smaller multiply very rapidly, the larger slowly. 
A physiological balance is maintained.” 
5. ‘‘The transmission of acquired characters. The advantages 
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 pro- 
gression or retrogression of the character.” 
6. ‘“‘Cross-breeding. ‘If when any peculiarity 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 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 man separated by distances of habita- 
tion, 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 men from apes, and is not 
applied to living things in general.” 
In addition to his theories as to the causes of evolution, Lamarck 
was the first to present the idea of the tree of life, or phylogenic tree, 
as a mode of representing animal relationships. All previous classifi- 
cations had been based on the idea of a single linear phylogenetic 
series, each lower group being supposedly ancestral to a higher group, 
and all in a single chain. 
We may best sum up Lamarck’s work and influence in the words 
of Osborn: " 
