Leonardo da Vinci (1452-1519), Vitruvian Man, c. 1490. Pen, ink and wash on paper, Gallerie dell’Accademia, Venezia

And from the first animals were developed, essentially by further differentiation, the numerous classes, orders, families, genera, and species of animals; and finally vertebrates, the form in which the nervous system attains its fullest development; and among these again finally that vertebrate in which nature attains consciousness of itself – man.

Friedrich Engels, Dialectics of Nature, Progress Publishers, Moscow, 1976, 33