The paper concerns phylogeny development of allergic reactivity, the most probable antecedents of allergic IgE antibodies, high affinity IgE receptor (Fc(epsilon)RI), presents comparative character of IgE - Fc(epsilon)RI and IgY- CHIR-AB1 interactions. The paper has given an insight of allergy as evolutionary selected reactivity for highly organized animals. This reactivity is directed to organization of allergen-specific inflammation and serves as biologically expedient, high-specific and high-sensitive reaction in response to allergen entering into the organism because of barrier tissue dysfunction. Such insight has raised a question on consequences of thoroughgoing allergy reactivity elimination for highly organized animals and their posterity.