The Evolution of the Human Placenta
Publication Year: 2012
Published by: The Johns Hopkins University Press
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Both of us authors are parents. We have experienced the joys (as well as the other emotions) of creating new life and nurturing and guiding that child to become an independent adult. Of course, our wives had a great deal to do with all of this as well. Indeed, at the very beginning they did almost all of the work! We are placental...
1. The History of Placental Investigations
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Humans have long speculated about the significance of the maternal-placental-fetal connection (Crofton Long, 1963; Jones and Kay, 2003). The placenta is viewed in different ways by different peoples. In modern Western culture it is primarily viewed medically. It is the afterbirth, sent to the pathology department possibly...
2. The Evolution of Live Birth in Mammals
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Producing live-born young is not unique to mammals; it isn’t even unique to vertebrates. Scorpions and other invertebrates, such as tunicates of the genus Salpa (salps) and some species of velvet worms, also produce live-born young. In these last two examples there is even a tissue connection between the maternal and embryonic...
3. Comparative Mammalian Placentation
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The placental mammal radiation has resulted in a wide range of species in terms of ecology, life history, and development. Not surprisingly, this diversity is reflected in a large variation in the level of neonatal development at birth among mammalian species. Neonates can be altricial (poorly developed) or precocial...
4. The Evolution of the Human Placenta
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Human beings are descendants of the anthropoid primate lineage. There have been many divergences over the roughly 60–70 million years since the anthropoid lineage came into being. Three major clades of anthropoid primates are generally recognized: the New World monkeys, the Old World monkeys, and the clade that includes...
5. Sex and the Placenta
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The diversity of placental structure, along with certain findings from molecular biology research, attest to the intense selective pressures this organ has been subjected to within the many mammalian lineages. It is an organ that has experienced considerable adaptive evolution. The placenta also appears to have affected...
6. Genes, Genetic Regulation, and the Placenta
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In 1983 Barbara McClintock (figure 6.1) was awarded the Nobel Prize in Physiology or Medicine for her work on the cytogenetics of maize. In particular, her work on transposons, the “jumping genes,” helped give her this well-deserved recognition. The discovery of the phenomenon of transposition, the ability of segments of DNA...
7. The Placenta as a Regulatory Organ
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Many kinds of regulatory systems exist, both within and outside of biology. An important distinction among them is that biological regulatory systems have evolved, and the process of evolution endows them with certain aspects that may not be present in a designed regulatory system. Frequently, redundancy of signaling...
8. Modern Gestational Challenges
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Modern human beings are an evolutionarily successful species. We have spread across the earth, and our population continues to increase at an impressive rate. It would seem that our reproductive adaptations are quite effective. Yet the processes of conception, implantation, gestation, and finally parturition in humans...
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Regulation, the ability to control, to greater or lesser extents, the internal environment in the face of external challenges, is a hallmark of life. This facet of life is perhaps most important during early development. Live birth evolved very early in the history of complex, multicellular organisms. We have argued that a primary...
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Page Count: 280
Illustrations: 2 halftones, 10 line drawings
Publication Year: 2012