acquired characteristics, modifications produced in an individual plant or animal as a result of mutilation, disease, use and disuse, or any distinctly environmental influence. Some examples are docking of tails, malformation caused by disease, and muscle atrophy. The belief in the inheritability of acquired characteristics, proposed by the French biologist Jean-Baptiste Lamarck in 1809, was widely accepted at one time, but is now rejected. Geneticists have affirmed that inheritance is determined solely by the reproductive cells and is unaffected by somatic (body) cells.