linkedin post 2018-08-11 03:48:37

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FRAGMENT FROM NATURE concerns that sweetest of birds, the common house sparrow. As a boy, I was forever in barn roofs surveying their nests, stealing the odd egg, and deeply engaged by these common and perky creatures. More recently, I have built up a decent colony in my home in Catalonia, starting with just a few individuals. Their global story is heart-wrenching. View in LinkedIn
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linkedin post 2018-08-10 04:14:00

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MALADAPTED BYPRODUCT. “Under Williams' hypothesis, the evolution of aging can be seen as a maladaptive byproduct of selection for survival and reproduction during youth. A fundamental corollary of Williams’ AP hypothesis is that early fitness components such as reproduction should genetically trade-off with late fitness components such as survival at old age, so that, for example, genotypes with high early fecundity should be shorter lived than those with low reproduction.” http://www.nature.com/scitable/knowledge/library/the-evolution-of-aging-23651151 View in LinkedIn
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linkedin post 2018-08-10 04:11:26

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ANTAGONISTIC PLEIOTROPY. "George C. Williams took Medawar's ideas a step further. If it is true that selection cannot counteract deleterious effects at old age, he argued, then mutations or alleles might exist that have opposite, pleiotropic effects at different ages: genetic variants that on the one hand exhibit beneficial effects on fitness early in life, when selection is strong, but that on the other hand have deleterious effects late in life, when selection is already weak.” http://www.nature.com/scitable/knowledge/library/the-evolution-of-aging-23651151 View in LinkedIn
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linkedin post 2018-08-10 04:09:32

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DELETERIOUS MUTATIONS. “The effects of such a mutation accumulation process would only become manifest at the organismal level after the environment changes such that individuals experience less extrinsic mortality (e.g., due to decreased predation) and thus live to an age where they actually express the symptoms of aging.” http://www.nature.com/scitable/knowledge/library/the-evolution-of-aging-23651151 View in LinkedIn
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linkedin post 2018-08-10 04:06:33

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MUTATION ACCUMULATION. "Medawar reasoned that, if the effects of a deleterious mutation were restricted to late ages, when reproduction has largely stopped and future survival is unlikely, carriers of the negative mutation would have already passed it on to the next generation before the negative late-life effects would become apparent. In such a situation, natural selection would be weak and inefficient at eliminating such a mutation, and over evolutionary time such effectively neutral mutations would accumulate in the population by genetic drift, which in turn would lead to the evolution of aging.” http://www.nature.com/scitable/knowledge/library/the-evolution-of-aging-23651151 View in LinkedIn
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linkedin post 2018-08-10 04:04:24

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SNUFFING MUTATIONS. “If a beneficial or deleterious mutation occurs only after reproduction has ceased, then it will not affect fitness (reproductive success) and can therefore not be efficiently selected for or against. However, even if a mutation occurs earlier, say during the reproductive period, its effects may not be visible to selection since, if extrinsic, environmentally imposed mortality is high, individuals that could express the mutation are likely to be dead already.” http://www.nature.com/scitable/knowledge/library/the-evolution-of-aging-23651151 View in LinkedIn
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linkedin post 2018-08-11 04:06:07

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RURAL REASONS. “This decline is in line with that of many other farmland species and is attributed to changes in farming practices: the switch from spring- to autumn-sown cereals; increased use of pesticides; increased use of herbicides; the switch from haymaking to cutting for silage before the grass has set seed; reduced spillage of grain and improved; storage to meet EU regulations.” https://www.britishbirds.co.uk/wp-content/uploads/article_files/V96/V96_N09/V96_N09_P439_446_A004.pdf View in LinkedIn
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linkedin post 2018-08-10 04:01:26

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EARLY DEMISE. “For most organisms, the natural world is dangerous since it abounds with competitors, predators, pathogens, accidents, and other hazards. It follows from this that in natural populations most individuals die or get killed before they can grow old and suffer the symptoms of aging: thus, individuals have a very small overall probability of being alive and reproductive at an advanced age.” http://www.nature.com/scitable/knowledge/library/the-evolution-of-aging-23651151 View in LinkedIn
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linkedin post 2018-08-11 04:04:45

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COUNTRY SPARROW POPULATIONS. “The House Sparrow index from 1970 to 1999, shows an increase up to 1979 followed by a decline of about 60%, although this had flattened out by 1995, suggesting that the farmland population has now stabilised at a new, lower level.” https://lnkd.in/ezA77j7 View in LinkedIn
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linkedin post 2018-08-10 03:58:45

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THE SELECTION SHADOW. "The key conceptual insight that allowed Medawar, Williams, and others, to develop the evolutionary theory of aging is based on the notion that the force of natural selection, a measure of how effectively selection acts on survival rate or fecundity as a function of age, declines with progressive age. As a consequence, selection is unable to favor beneficial effects, or to counteract deleterious effects, when these effects are expressed at advanced ages.” http://www.nature.com/scitable/knowledge/library/the-evolution-of-aging-23651151 View in LinkedIn
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