During his studies of the life cycle of aphids, Charles Bonnet discovered parthenogenesis, that is, reproduction without fertilization.
Bonnet, the only son in a wealthy family, was a lawyer by profession, but he devoted most of his life to the study of natural history and philosophical writing. Entomology, the study of insects, became one of his favorite pursuits. After reading Réné Antoine Ferchault de Réaumur's (1683-1757) History of Insects, Bonnet began corresponding with the famous French scientist in 1738. Two years later, Bonnet had extended some of Réaumur's experiments on aphids and was able to prove that female aphids were able to reproduce without fertilization by the male. Females that hatched during the summer gave birth to live offspring without fertilization. In the autumn the new generation of males and females mated and the females laid eggs, but by carefully isolating and feeding young females Bonnet was able to raise many generations of aphids by parthenogenesis. Bonnet's remarkable studies were presented to the prestigious French Academy of Sciences by Réaumur and published by Bonnet as his Treatise on Entomology in 1745.
Bonnet's studies of parthenogenesis were accepted by many other naturalists as compelling evidence in support of ovist preformationism. According to Bonnet, every female contained the germs, or eggs, of all creatures that would originate from her. When provided with the proper stimulus and nutrition, the preformed germ was able to grow. Usually, male semen was needed to initiate growth; but the female parent provided the nutrition needed for all further stages of development. Despite many difficulties posed by preformationist theories, Bonnet's work was still respected by many nineteenth century naturalists.
In 1744, Bonnet began to experience severe eye pain that made it difficult for him to use the microscope. Nevertheless, he was able to carry out important studies of insect metamorphosis. He also demonstrated that caterpillars and butteries breathed through pores, which he named stigmata. As his eye disease progressed, Bonnet turned to the study of botany. His Research on the Function of Leaves of Plants (1754) described his observations on plant nutrition and the structure and function of plant leaves. Finally, when blindness forced him to give up microscopic investigations entirely, Bonnet became interested in more abstract and philosophical pursuits. With the assistance of a secretary, Bonnet prepared his Contemplation of Nature, which explored his general philosophy of nature (1762, 1764). He also corresponded with many of the most eminent scholars and experimentalists of his era.
Bonnet was the first to use the term "evolution" in a biological context and to propose a catastrophe theory of biological evolution. In a treatise called The Philosophical Revival (1769), Bonnet analyzed the implications of contemporary reports of fossil evidence that many species had become extinct. Bonnet suggested that the Earth periodically suffered universal catastrophes, which destroyed almost all life forms. Those that survived were able to move up the evolutionary scale.
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