Wilhelm Ludvig Johannsen
On this date, the Danish botanist and geneticist Wilhelm Ludvig Johannsen was born. His experiments in plant heredity offered strong support to the mutation theory of the Dutch botanist Hugo de Vries (that changes in heredity come about through sudden, discrete changes of the heredity units in germ cells). Many geneticists thought Johannsen’s ideas dealt a severe blow to Charles Darwin’s theory that new species were produced by the slow process of natural selection.
Johannsen explained his ideas in his book entitled On Heredity and Variation (1896), which he revised and lengthened with the rediscovery of Gregor Mendel’s laws and reissued as The Elements of Heredity in 1905. The enlarged German edition of this work was published in 1909 and became the most influential book on genetics in Europe. In it, Johannsen coined the terms “gene”, “phenotype”, and “genotype”.
Illustration of fossil Iguanodon teeth with a modern iguana jaw from Mantell’s 1825 paper describing Iguanodon.
On this date, the British physician, geologist, and paleontologist Gideon Algernon Mantell was born. He discovered 4 of the 5 genera of dinosaurs known during his time.
Mantell’s life-long hobby was all-consuming. While walking with his wife in 1822, he discovered fossils that he identified as teeth. When he saw the connection with teeth of the present lizard, the iguana, in 1825, he named the animal the Iguanadon (“fossil teeth”). Subsequently, he made additional finds of fossil bones of other large animals which he described accurately: the Hylaeosaurus, Pelorosaurus, and Regnosaurus. His contemporary, paleontologist Sir Richard Owen, coined the word dinosaur (“terrible lizards”). Mantell’s books include Medals of Creation (1844).
First fossil skull of Australopithecus.
On this date, a report of a fossil closely related to humans, found by Raymond Dart in 1924, was published in a newspaper. The Star of Johannesburg, South Africa announced the find, instead of the professional journal Nature, when the editors of the journal changed their mind. With his students, Dart had made the discovery in the Taung limestone works in the Harts Valley of Bechuanaland. When an endocranial cast was found, at first it seemed to be just another primate skull. Then, Dart noticed how amazingly close to human it looked. He had discovered the remains of what came to be known informally as the “Taung child“, who was only three years old at the time of death. He named it Australopithecus africanus,” australis” meaning south and “pithecus” meaning ape. His theory is now generally accepted, but was originally very controversial.