The word "atavism" meets in modern life quite often – however, usually physicians and scientists operate with it only. What this mysterious word what it can be applied to means and in relation to whom it is used?
Word meaning "atavism"
Atavism (the translation from Latin - the great-great-grandfather) call emergence at living beings of signs which were peculiar to their very far ancestors. Characteristic signs of atavism are excess mammary glands, tail appendages, dense indumentum on a human body and also a mnogopalost at animals. Genes which for various reasons can become more active in an organism later many generations are responsible for emergence of these signs.
At normal development without pathologies the atavisms are not shown as their genes are blocked by other healthy genes.
Darwin leaned on the phenomena of atavism, proving phylogenetic origin of different types with their help. Besides, the scientist claimed that atavism is shown as a result of crossing of animals or plants which result is a hybridization and activization of the sleeping genes causing atavism. Modern geneticists and embryologists considerably narrowed this concept therefore atavism is more often mentioned only in popular scientific literature today.
Signs of atavism
Atavistic signs can arise in the different ways. So, spontaneous atavism when at a certain look signs unusual for it which, nevertheless, were noted at his distant ancestors from other systematic categories are shown is most often noted. For example, at horses foals with three fingers or striped coloring are born, or the person has a tail-shaped shoot. Also atavism is shown in a hyper trichosis, a polimastiya or a kriptorkhizm which are most often noted at members of the human species. Unlike atavistic manifestations, rudimentary signs meet at all representatives of any given look. Besides, the atavism phenomena often prove as a result of regeneration processes – for example, at crayfish instead of an eye the claw can grow, and at loss of a claw at some types its growth connected with more ancient phylogenetic type is observed. Similar cases meet also at Orthoptera which pads often regenerate in the extremities reminding legs of the lowest in development forms. With atavism such pathological phenomena as the mikrotsefaliya, a cleft lip and many other signs resulting from the wrong pre-natal development of a fruit have nothing in common.