Maupertuis Provides Evidence of “Hereditary Particles”

The theory of hereditary particles had been competing with other possible explanations of biological reproduction in 1751. However, with the publication of Système de la nature, Maupertuis became the first scientist to provide statistical evidence that the existence of particles inherited from both parents could explain specific, empirically observable patterns in the inheritance of physical traits.

Summary of Event

During the eighteenth century, there existed several theories of reproduction, Human reproduction
Reproduction, human
Embryology;and heredity[heredity] but the most prominent theories involved either embryonic preformation or epigenesis. Preformation theories Preformation theories (embryology) considered the embryo to have already been formed as a miniature human. Taken to its extreme, this theory held that all humankind was formed at creation as persons within persons, something like Russian nesting dolls. Therefore, the biblical Adam and Eve, called the mother and father of all humankind, were considered literally to have all humankind already preformed within them. [kw]Maupertuis Provides Evidence of “Hereditary Particles” (1751)
[kw]Particles”, Maupertuis Provides Evidence of “Hereditary (1751)
[kw]”Hereditary Particles”, Maupertuis Provides Evidence of (1751)[Hereditary Particle]
[kw]Evidence of “Hereditary Particles”, Maupertuis Provides (1751)
Heredity
Embryology
Genetics
[g]France;1751: Maupertuis Provides Evidence of “Hereditary Particles”[1330]
[c]Biology;1751: Maupertuis Provides Evidence of “Hereditary Particles”[1330]
[c]Science and technology;1751: Maupertuis Provides Evidence of “Hereditary Particles”[1330]
[c]Health and medicine;1751: Maupertuis Provides Evidence of “Hereditary Particles”[1330]
Maupertuis, Pierre-Louis Moreau de

Preformationists were divided into ovists, Ovist-spermist debate (embryology)[Ovist spermist]
Spermist-ovist debate (embryology)[Spermist ovist] who believed that the preformed offspring resided in the female’s eggs, Gametes and spermists, who believed that the preformed offspring resided in the male’s sperm. Some spermists even claimed the existence of a little human, called a homunculus, Homunculus (little human) “crouching” within sperm. One problem with preformationism involved defining the role of the two sexes. Ovists considered the semen as simply nourishment for the embryo carried in the female. Spermists considered the female as simply the receptacle for the embryo that grew from the homunculus in the sperm. Another problem involved the apparent waste. What happened to eggs in the female that never received nourishment? After biologists discovered the vast numbers of sperm in semen, the apparent waste was even more troublesome. Would God Religion;and human reproduction[human reproduction] design a system, it was wondered, in which so many preformed offspring were simply lost?

Preformation was problematic on a more practical level as well. If Eve or Adam contained all humankind within them when they were created, how could all the billions of future humans be contained in such a small space? Those who believed in the infinite divisibility of matter saw no difficulty; the embryos would just be smaller and smaller to infinity. As the structure of matter became better understood, however, it became clear that such a large number of ever-smaller humans could not possibly fit within Adam or Eve, because that would require the embryos to be smaller than the ultimate minimum size of matter.

Once embryo development had been observed microscopically, it became apparent that early embryos did not resemble miniature adults. Embryos started as clumps of cells Cellular biology that increased in size and gradually developed arms, legs, and other human features. These observations led to the gradual acceptance of the theory of epigenesis, Epigenesis that is, the gradual development of the human form. The latter theory also supplanted that of preformation, because it allowed for simultaneous roles for both the egg and the sperm in reproduction.

Because children Children;and heredity appeared to possess some combination of characteristics from both parents, it was reasoned that these traits must be inherited via both the sperm and the egg. This realization led to a blending theory of inheritance: Blending theory of inheritance The sperm and egg were considered to be an aggregation of cells that migrated from all over the body. When the sperm and egg joined together in the uterus, the resulting embryo was therefore composed of cells derived from both parents. Children resembled both parents because their cells were literally derived directly from collections of cells derived from each parent.

Pierre-Louis Moreau de Maupertuis considered epigenesis to be the correct explanation for reproduction, but he differed somewhat in certain details. He did not believe that the sperm or egg had anything directly to do with reproduction; both simply provided nourishment of some sort for the collections of particles provided by each of the parents. He believed that particles migrated from various parts of the male body and congregated in the seminal fluid. When this seminal fluid was deposited into the woman’s reproductive tract, particles from her body migrated to the uterus and, together with the particles from the male, they formed the embryo. The cells possessed some sort of memory about their position in the parent’s body that allowed them to migrate to the proper positions in the developing embryo. The balance of the number of cells from each parent determined the characteristics of the developing child. The parent that contributed the greater number of particles expressing a specific anatomical characteristic was dominant over the other parent, and the former parent’s trait would be expressed rather than the latter’s.

Maupertuis’s interest in mutants, especially the two distinctive human mutations of albinism Albinism and polydactyly Polydactyly (possession of extra fingers or toes), led him to apply statistics to the problem of inheritance. In 1744, an albino boy, born to a pair of African slaves in South America, was brought to Paris to be displayed to the members of the French Academy of Sciences, Academy of Sciences, France of which Maupertuis was a member. As a vehicle to discuss his theories on reproduction and inheritance, Maupertuis wrote about this African albino in the anonymously authored book Dissertation physique à l’occasion du negre blanc
Dissertation physique à l’occasion du negre blanc (Maupertuis) (1744; physical dissertation occasioned by the albino negro). He chose to present his ideas about the “corpuscles,” or particles, involved in reproduction in this anonymous manner, because he feared that presenting such a provocative theory to the Academy of Sciences could affect his scientific reputation. He later expanded the book to include discussion of other traits, most notably polydactyly, under the name Venus physique (1745; The Earthly Venus, Earthly Venus, The (Maupertuis) 1966).

With the publication of Système de la nature
Système de la nature (Maupertuis) (1751; system of nature), again anonymously, Maupertuis gave his most complete exposition on inheritance. He included an extensive pedigree of the family of the Berlin surgeon Jacob Ruhe, in which polydactyly appeared in a number of individuals. Using this pedigree, he was able to show that polydactyly could be passed from an affected person to that person’s offspring, whether the person was male or female. This supported Maupertuis’s contention that particles were passed to children from both of their parents.

Maupertuis also applied statistical reasoning to the occurrence of polydactyly, comparing its incidence in the Ruhe family with its occurrence in the general population. Based on his estimate that the occurrence of polydactyly in the general population was approximately 5 in 100,000, he calculated the probability of a parent with polydactyly having a child with the trait solely by chance to be 1 in 20,000. Therefore, he reasoned, the occurrence of this condition throughout the Ruhe family line must be accounted for by inheritance and not by chance. He further concluded that because of its high occurrence in the Ruhe family, polydactyly must be a “dominant” trait.

Significance

In many ways, Maupertuis’s theories on inheritance, as outlined in Système de la nature, were revolutionary. Recognition that inheritance somehow involved particles that came together to form the embryo enabled Maupertuis to develop a theory of inheritance that was consistent with scientific observations. His use of statistics Statistics;biology in researching biological inheritance was a first, and it was not until more than one hundred years later that Gregor Mendel would put statistics to a similar use.

Some historians of science have tried to credit Maupertuis with the first correct model of inheritance, allowing him to supplant Mendel as the father of genetics. Genetics Although Système de la nature represented a step forward, however, Maupertuis’s theory of inheritance was lacking on two counts. First, Maupertuis saw no role for the gametes (eggs and sperm) and considered the particles that made up the embryo to be corpuscles contained in the female’s reproductive tract and in the male’s semen. Therefore, the particles of inheritance described by Maupertuis were different than those described by Mendel, who believed they were contained in the gametes.

Second, Maupertuis’s use of the term “dominance” was different from that of Mendel. In Maupertuis’s theory, dominant particles were simply more active and therefore often outcompeted “normal” particles. In other words, Maupertuis envisioned multiple hereditary particles competing for spaces in the developing embryo and defined dominant particles as those that were more likely, but not guaranteed, to win the “competition.” He did not believe that the “winner” was predictable in a given case. Mendel, on the other hand, thought that each gamete contained one particle corresponding to each trait: When brought together in the embryo, dominant particles always masked the effects of “recessive” particles. Therefore, although Maupertuis’s ideas were revolutionary, they lacked certain details that would emerge later in Mendel’s more accurate theory of particulate inheritance in the nineteenth century.

WikiSummaries

Free Book Summaries

Categories

Maupertuis Provides Evidence of “Hereditary Particles”

Categories

Related posts: