In the period during which Darwin developed the theory of evolution, the question of how living things transmitted their characteristics to later generations was unknown. Therefore, primitive conjectures such as traits being transmitted by way of the blood were widely accepted. This uncertainty about the mechanisms of heredity led Darwin to predicate his theory on a range of completely erroneous assumptions.
He pointed to natural selection as the basis of the evolutionary mechanism. Yet if beneficial attributes were chosen by means of natural selection (the survival of the fittest"), how could they be transmitted from one generation to another? At this point, Darwin embraced the thesis, which Lamarck had proposed, of "the transmission of acquired characteristics."
However, Lamarck's thesis was refuted when the laws of inheritance discovered by the Austrian botanist and also a priest Gregor Mendel. This meant that beneficial traits could not be passed along. Genetic laws demonstrated that acquired features were not handed on, and that inheritance took place according to immutable rules-which by implication supported the idea of the immutability of species.