a trait that originates during some stage of an organism’s individual development under the influence of environmental change. This influence can act indirectly by means of altered function, for example, it can intensify or decrease the activity of an organ, or it can act directly.
The study of acquired characters was important in view of a long-standing debate on the heritability of these traits. One point of view acknowledged the Lamarckian principle of direct adaptation, that is, the heritability of acquired changes. The opposing point of view was the Darwinian principle of evolution on the basis of undetermined hereditary variability and natural selection. The resolution of this debate was a milestone in the history of evolutionary thought. In the absence of strictly controlled experiments in Darwin’s time, which would have permitted evaluation of the heritability or nonheritability of acquired characters, Darwin accepted the feasibility of two paths of evolutionary development: in addition to evolution by natural selection, he admitted the possibility, although with reservations, that evolution proceeded through direct adaptation.
From the end of the 19th century until the 1930’s, many attempts were made to experimentally confirm the existence of somatogenic changes in an organism, that is, changes that do not involve sex cells. In particular, such changes occur under the influence of mechanical injuries, unusual temperatures, or unusual lighting or moisture conditions; chemical agents, including immunologie substances, may also produce such changes.
The results of these experiments were not convincing, since the following procedures were not observed. Genetic homozygosity of experimental subjects was not verified in preliminary crossbreeding experiments; that is, researchers failed to prove an absence of segregation over several generations with respect to those characters whose heritability or nonheritability was being investigated. The use of an external agent to produce changes in the parent individuals was not consistent from experiment to experiment. The offspring of changed parents were not transferred to the same environmental conditions under which the parents had been living before the parental changes had occurred. Once a new character appeared in the first-generation offspring of parents who had acquired that character, studies were not carried out to discover whether the character would segregate in crossbreedings between changed individuals and unchanged individuals.
Subsequent experiments, which disproved the heritability of acquired characters, were completely convincing, since all of the above procedures were followed. Similarly, old experiments were refuted that had claimed to confirm the heritability of acquired behavioral changes as well as the heritability of host-effected changes in transplanted ova or in sex cells of transplanted gonads. Finally, experiments that had used blood transfusions or vegetative hybridization were also refuted. Thus, the nonheritability of acquired characters is a well-accepted fact today.
L. Ia. BLIAKHER