Dialectics and its study was derived from Hegel who had studied the Greek philosopher Heraclitus. Heraclitus taught that everything was constantly changing and that all things consisted of two opposite elements which changed into each other as night changes into day, light into darkness, life into death etc.
Engels's work follows on from what Engels had said about science in Anti-Dühring. It includes the famous The Part Played by Labour in the Transition from Ape to Man, which has also been published separately as a pamphlet. Engels argues that the hand and brain grew together - an idea supported by later fossil discoveries, though it seems the foot came first. (See Australopithecus afarensis: Bipedalism.)
Most of the work is fragmentary, but it has points of interest. In biology, he says: