Linnaeus, Lamarck, Cuvier and Darwin

Carl Linnaeus (1707–1778) described plant and animal species, built a hierarchical system (species, genus, family, order, class) and introduced the rule of giving species two-word (binomial) names (Systema Naturae, 1735). His system was artificial – plants were divided into 24 classes by a few features such as the number of stamens, so unrelated ones fell into one group; Linnaeus held that species do not change. Jean-Baptiste Lamarck (1744–1829) created the first complete evolutionary theory (“Philosophie zoologique”, 1809), introduced the terms “biology” and “invertebrates” and divided animals into 14 classes. He held that organisms change from simple forms to more complex (gradation), that organs develop with exercise and weaken with disuse, and that changes acquired during life pass to offspring. The second part – inheritance of acquired characters – was not confirmed by later experiments: modifications are generally not inherited (epigenetic effects are an exception, and even they are not the classic Lamarckian mechanism). Georges Cuvier (1769–1832) developed the principle of correlation – the organs of an animal are interrelated – and with it could reconstruct a whole animal from bones; he was one of the founders of palaeontology. Although he identified extinct species, he explained their disappearance by catastrophes and held that species do not change. K. Baer discovered the mammalian egg cell in 1827; in 1838–39 M. Schleiden and T. Schwann created the cell theory – all organisms are made of cells, showing the unity of the living world.