This year, the French are commemorating the centenary of the death of their distinguished countryman Louis Pasteur, chemist and bacteriologist. Yet few people in France or elsewhere will be aware of a fact which I recently discovered: Louis Pasteur and the Czech geneticist Gregor Mendel were born in the same year - 1822. That Pasteur and Mendel are exact contemporaries is a most significant coincidence, for their respective careers symbolize the parallel and contiguous development of medical and genetic knowledge in the nineteenth century. This in turn paved the way for man to discuss, investigate, increase and spread understanding of human reproduction, disease and life-span, and to utilize scientific understanding of these subjects to increase the well-being of mankind in the twentieth century. Indeed, the human relevance of these biomedical discoveries caused them to eclipse those of other branches of knowledge in this century.