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The History of Genetics - Early Beliefs About Heredity

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From the earliest recorded history, ancient civilizations observed patterns in reproduction. Animals bore offspring of the same species, children resembled their parents, and plants gave rise to similar plants. Some of the earliest ideas about reproduction, heredity, and the transmission of information from parent to child were the particulate theories developed in ancient Greece during the fourth century B. C. These theories posited that information from each part of the parent had to be communicated to create the corresponding body part in the offspring. For example, the particulate theories held that information from the parent's heart, lungs, and limbs was transmitted directly from these body parts to create the offspring's heart, lungs, and limbs.

Particulate theories were attempts to explain observed similarities between parents and their children. One reason these theories were inaccurate was that they relied on observations unaided by the microscope. Microscopy—the use of or investigation with the microscope—and recognition of cells and microorganisms did not occur until the end of the seventeenth century, when English naturalist Robert Hooke (1635–1703) first observed cells through a microscope.

Until that time (and even for a time after), heredity remained poorly understood. During the Renaissance (from about the fourteenth to the sixteenth centuries), preformationist theories proposed that the parent's body carried highly specialized reproductive cells that contained whole, preformed offspring. Preformationist theories insisted that when these specialized cells containing the offspring were placed in suitable environments, they would spontaneously grow into new organisms with traits similar to the parent organism.

The Greek philosopher Aristotle (circa 384–322 B. C.), who was such a keen observer of life that he is often referred to as the "father of biology," noted that individuals sometimes more closely resemble remote ancestors than their immediate parents. He was a preformationist, positing that the male parent provided the miniature individual and the female provided the supportive environment in which it would grow. He also refuted the notion of a simple, direct transfer of body parts from parent to offspring by observing that animals and humans that had suffered mutilation or loss of body parts did not confer these losses to their offspring. Instead, he described a process that he termed "epigenesis," in which the offspring is gradually generated from an undifferentiated mass by the addition of parts.

Of Aristotle's many contributions to biology, one of the most important was his conclusion that inheritance involved the potential of producing certain characteristics rather than the absolute production of the characteristics themselves. This thinking was closer to the scientific reality of inheritance than any philosophy set forth by his predecessors. Since, however, the father of biology was developing his theories before the advent of microscopy, he mistakenly presumed that inheritance was conveyed via the blood. Still, Aristotle's enduring influence is evident on our language and thinking about heredity. Despite the fact that blood is not the mode of transmission of heredity, we still refer to "blood relatives," "blood lines," and offspring as products of our own "flesh and blood."

One of the most important developments in the study of hereditary processes came in 1858, when Charles Darwin (1809–82) and Alfred Wallace (1823–1913) announced the theory of natural selection—the idea that members of a population who are better adapted to their environment will be the ones most likely to survive and pass their traits on to the next generation. Darwin published his theories in On the Origin of Species by Means of Natural Selection (London: John Murray, 1859). Darwin's work was not viewed favorably, especially by religious leaders who believed that it refuted the biblical interpretation of how life on Earth began. Even in the twenty-first century the idea that life evolves gradually through natural processes is not accepted by everyone, and the dispute over creationism and evolution continues.

The History of Genetics - Cell Theory [next]

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