The Law of Conservation of Mass dates from Antoine Lavoisier's 1789 discovery that mass is neither created nor destroyed in chemical reactions. In other words, the mass of any one element at the beginning of a reaction will equal the mass of that element at the end of the reaction.
Variations in evolution usually refers to variation of genes at a particular loci. This differs from diversity which is the total of genetic differences within a population. Speciation is the reproductive isolation of a subset of a population.
