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According to this model both males and females contribute a fluid to children. In addition, each part of the body contributes a fluid (e.g., eye fluid, finger fluid). At conception, the fluids compete, and gender is determined by this competition.
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Spontaneous generation was the idea that living organisms could arise from a nonliving substance. Flies, for example, spontaneously generated from meat, and fleas from mud and dirt.
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William Harvey publishes De Generatione Animalium. Harvey argued by analogy that women have eggs because chickens have eggs, and he was one of the first to argue that human reproduction occurs through epigenesis, the development of an organism from the fusion of sperm and egg.
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Published the article Experiments on the Generation of Insects.
Conducted one of the first controlled experiments by placing meat into jars (some covered, some uncovered). He disproved spontaneous generation by showing that flies did not spontaneously generate from the meat in covered jars. -
Leeuwenhoek made tremendous improvements to microscopes, specifically the lens. He observed both fleas mating and sperm. He deduced that all organisms are sexual and speculated that sperm might have a preformed individual inside that develops in utero.
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Needham tested his theory that heat killed microorganisms by heating gravy and letting it cool. Upon examining the gravy with a microscope, he discovered that microorganisms sill existed. He believed the microorganisms' existence supported spontaneous generation.
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Spallanzani argued that microorganims were in the air, but could not survive one a container was heated and sealed.
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Pasture combined the works of Needham and Spallanzani by proving that microorganims were indeed airborne. He then demonstated that the intrduction of microorganims to the growth medium could be controlled. This resulted in the breakthrough we call pasteurization. It also finally disproved spontaneous generation.
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Mendel performed detailed experiments on seven traits of the pea plant. He established laws of heredity that serve as the basis for the modern study of genetics.
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Morgan was awarded a Nobel prize for his work in Genetics. His experiments with fruit flies lead to his discovery that genes were located on chromosomes which are the molecular basis of heredity.
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The Human Genome Project started in 1990 and was completed in 2003. The projects main goals were to identify all the genes in human DNA (20,000-25,000) and to determine the nucleotide sequence for all of the genes (3 billion bases).
