Alfred Russel Wallace (1823-1913)
Wallace was an English naturalist who traveled extensively, first to Brazil and then to the Indonesian archipelago, collecting and studying local specimens. He is considered the co-discoverer of natural selection together with Charles Darwin. When Wallace was ready to publish his theory, he wrote a letter to Darwin giving him the news. Darwin had spent 20 years developing his theory and had not published it yet for fear of the public reaction and especially that of his wife. Wallace’s theory was presented in London at the Linnean Society on July 1, 1858, along with Darwin’s theory. In fact, the two ideas differ to some degree: Darwin went much further than Wallace. Wallace set a limit to natural selection when it came to humans.
He never conceived the human soul as a result of evolution; he claimed it had a divine origin. On the other hand, Darwin knew well that man is just another primate. All the features of our species, without any exception, must have been the result of adaptations. Besides, Wallace never supported sexual selection; he never reached an agreement with Darwin on this topic.
Charles Lyell (1797-1875)
Lyell was an English geologist who published in Darwin’s time a treatise called Principles of Geology. He suggested that the Earth has undergone enormous transformations over its history, for long periods. It is the geological forces, like earthquakes, floods, volcanic eruptions, and erosion, acting one after the other, that produce all the features we see. His book shows an image of the Temple of Serapis in Pozzuoli, Naples. It is what remains of a once lively Roman market but serve as proof of Lyell’s geological theory. There are three marble columns right in the middle, which show a section of about 3 meters long of material that was damaged by repeated floods and eruptions.
When seawater covered the columns, clams called Lithodomes ate some material causing the damage that is visible today. Furthermore, volcanic material produced during one or more eruptions covered them until 1749, when excavations at the site took place. Lyell’s was one of the books that inspired Darwin because it offered a theory for the immensity of time that evolution requires to happen.
Ernst Haeckel (1834 – 1919)
Haeckel was a German biologist, philosopher, and artist, defender of Darwin’s ideas. He is famous for the detailed drawings that he made of countless species, and by coining terms like stem cells, anthropogeny, and ecology. He is also well known for having been the first to attempt to classify all the species in a tree of life. But what made him most famous is his theory of recapitulation: ontogeny recapitulates phylogeny. With this, he claimed that the biological development of an organism, or the embryo (ontogeny) summarizes all the intermediate forms of its ancestors throughout the evolution of the species (phylogeny). Nowadays, this theory is considered outdated.
Haeckel was an excellent illustrator. He published a compilation of color and black/white plates, titled Art Forms in Nature, consisting of 100 beautiful prints of many different organisms, many of them first discovered and described by himself. Some of the most outstanding ones are the anemones and other jellyfish, bats, octopuses, spiders, plankton, trilobites, and many more microscopic marine creatures.
Gregor Mendel (1822-1884)
Mendel was an Augustinian monk born in Austria who experimented with pea plants and discovered the laws of inheritance. Without even knowing the existence of genes, Mendel found that it was possible that some recessive traits could reappear in future generations. We know that he wrote once to Darwin to share his discovery, but Darwin received the letter, put it in a drawer and never read it. That letter was found after Darwin’s death. One cannot avoid wondering what Darwin would have thought about someone experimentally proving what he supposed to happen in theory. Mendel found that traits came in pairs, were inherited from father and mother, and could be either dominant or recessive.
What Mendel discovered is that if we breed together a population of yellow and green peas, where the yellow color is a dominant trait (AA), and the green color is recessive (aa), the offspring in the first generation will only be yellow peas (Aa). The second generation will get all possible combinations of the trait (AA, Aa, aA and aa). The result will be a ratio 1:3. Green peas will reappear. It was until the 20th century when genes were discovered that the genius of Mendel’s work received the credit he deserved.