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Tlie Pliysical Basis or Heredity 



Two influences enter into the making of every plant, animal and man — 

 their inheritance and their surroundings. Nature and nurture are never sepa- 

 rated but nature once set is steadfast and harder to change than nurture. A 

 hen sits on ducks' eggs and hatches ducks but no hen broods ducks' eggs into 

 chickens. Monkeys learn to climb trees; cows never do. 



The question "Which is more important, heredity or environment?" has 

 started endless arguments, but it was never a sensible question for no plant 

 or animal can exist without both. Although inseparable, they are different. 

 By the time an animal has come into existence as a fertilized egg, its in- 

 heritance has been set, heredity is behind it. Nobody chooses his parents 

 and the inheritance they give him. But most of his environment is still in 

 front with chances of change and choice. 



What is Heredity? The heredity of a plant or animal consists of the 

 characteristics brought to it by its ancestors. People of every kind, climate 

 and time, have had their own ideas and uses of inheritances. In their early 

 history, the Egyptians selected and artificially pollinated their date palms 

 and got a better crop of dates. In the middle ages, the big horses capable of 

 carrying the enormous weight of the armored knights were selectively bred 

 and became the ancestors of the English Great Horse or Shire Horse. In 

 later times, many new types, such as mules and Poland-China hogs, have 

 been produced by crossing different varieties and species. Hardy range-sheep 

 come from crosses of Merino and "mutton sheep." From time immemorial 

 human beings have looked at one another and recognized that like begets 

 like; so have the robins and rabbits and other animals according to their 

 kind. 



What is Genetics? Genetics is the science of the genes, the physical units 

 of heredity contained in the chromosomes and believed to be protein mole- 

 cules. Studies of genetics are precise and analytical, usually focused on single 

 or small groups of inherited characters and often based on experiments. 



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