World survey of the common XXXX : developmental error or genetic variant?

@entity1 @entity455 @entity235 @entity95 @entity2461 @entity600 @entity299 @entity35 @entity34926
The common @entity299 are prevalent throughout the world, in countries of high technology and among the primitive races. These same @entity600 were described 200 years ago, @entity34926 5,000 years ago. Their recent increase is directly related to the advent of cardiac treatment. Most @entity299 known to @entity1 occur in the @entity235 . The prevalence rate of these @entity600 is the same in the @entity235 and in @entity1 (5-8/1,000). Several of the @entity600 are heritable in specific breeds of @entity235 , one in @entity95 , another in @entity35 . These @entity600 occur in various animals that cannot interbreed. Hence the deoxyribonucleic acid (DNA) that codes these @entity600 must lie in that portion of the DNA common to all mammals. This suggests that these @entity600 occurred during the evolution of the @entity1 . Mammals evolved from reptiles, animals with hearts of various structures for the @entity455 . Although the "normal" heart is the most compatible with @entity1 life and hence the most common, some mammals may have evolved with a heart with different structures for the @entity455 . Some of these hearts have persisted. These primeval hearts we call @entity299 of the cyanotic group. Malformations that apparently are arrests in the development of the normal heart ( @entity2461 , atrioventricular canal) may represent stages in the evolution of the "normal" heart. Although teratogens and mutagens do exist, the author conceives of @entity299 not as arrests or errors in the development of a "normal" heart but as genetic variants.
