Month: September 2022

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

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

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

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

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

INTERDEPENDENCE. “The house sparrow, Passer domesticus is unique among wild birds in its close association with virtual dependence on man, not only in the agricultural environment, where presumably this association first evolved, but also in built-up areas. It would be expected that, with man’s dominance of the world, the future would be a bright for house sparrows, but it is now becoming an evident that this is not the case, particularly in the urban and sub-urban areas.” https://lnkd.in/e6evZ-H View in LinkedIn

MASSIVE LOSSES. “Common birds such as sparrows, starlings and skylarks are suffering "alarming" declines in their numbers, a new study has warned. Figures from bird monitoring schemes suggest that populations of the most widespread species have dropped by around 421 million across Europe since 1980.” https://lnkd.in/eCjmgmA View in LinkedIn

THIRTY YEAR FINDING. “The decline of the house sparrow in the UK is a relatively recent phenomenon. From around 13 million pairs in the early 1970s, numbers are now estimated to stand somewhere between 2.1 and 3.7 million: a 71 per cent drop in the national breeding population from 1977 to 2008.” https://lnkd.in/eTu-5Ri View in LinkedIn

HOUSE SPARROW. “In December 2002, the Telegraph Magazine considered the species’ appearance on the Red List of UK endangered species.” https://lnkd.in/ezA77j7 View in LinkedIn

CANARY IN THE MINE. “The House Sparrow Passer domesticus population in Britain suffered a major decline in the 1920s, particularly in built-up areas, which coincided with the replacement of the horse by the internal combustion engine.” Not just from toxic fumes but from the loss of the oat spill from horse feed bags. https://www.britishbirds.co.uk/wp-content/uploads/article_files/V96/V96_N09/V96_N09_P439_446_A004.pdf View in LinkedIn