If a single cell, under appropriate conditions, becomes a man in the space of a few years, there can surely be no difficulty in understanding how, under appropriate conditions, a cell may, in the course of untold millions of years, give origin to the human race.
Herbert Spencer, The Principles of Biology, Vol 1
analogy, biology, cell, common-ancestor, embryology, evolution, heredity, homo-sapiens, human, millions-of-years, origin, science, understanding, universal-common-ancestor