File Name: darwinian populations and natural selection .zip
Interactions among microbial cells can generate new chemistries and functions, but exploitation requires establishment of communities that reliably recapitulate community-level phenotypes. Using mechanistic mathematical models, we show how simple manipulations to population structure can exogenously impose Darwinian-like properties on communities.
For Darwin, natural selection is a drawn-out, complex process involving multiple interconnected causes. Natural selection requires variation in a population of organisms. That struggle is itself the result of checks on the geometric population increase that would occur in the absence of the checks. All populations, even slow-breeding ones such as those of elephants, will increase in size in the absence of limitations on growth that are imposed by nature. These checks take different forms in different populations.
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If there is a single discipline of science calling the basic concepts of biology into question, it is without doubt microbiology. Indeed, developments in microbiology have recently forced us to rethink such fundamental concepts as the organism, individual, and genome. In this paper I show how microorganisms are changing our understanding of natural aggregations and develop the concept of a Darwinian population to embrace these discoveries. I start by showing that it is hard to set the boundaries of a Darwinian population, and I suggest thinking of a Darwinian population as a relative property of a Darwinian individual. Then I argue, in contrast to the commonly held view, that Darwinian populations are multispecies units, and that in order to accept the multispecies account of Darwinian populations we have to separate fitness from natural selection.
According to Ernst Mayr, population thinking is a metaphysical theory. Mayr's essentialism, amounts to the view that types, including conceptual categories, are real while individual variation is illusionary. In contrast, population thinking entails the opposite view: Types are not real in nature, only individuals exist. According to Sober, the explanatory goal for essentialists is to find an underlying order that unites and underlies the variation one sees in nature. Population thinking as a methodological doctrine states that regularities that occur in populations such as extinction, speciation, and adaptation emerge from the collective activities of individuals. Such population phenomena were unknown until new statistical measures introduced by Laplace provided the proper resolution to detect population changes. There are two types of population thinkers, statisticians, and force theorists.
Fifteen second chromosomes were extracted from Drosophila willistoni flies collected in four natural populations. The adaptedness of populations homozygous for each chromosome was measured by average population size and productivity. The Darwinian fitness of flies homozygous for each wild second ehromosome, and of flies carrying random combinations of these chromosomes, was measured relative to the fitness of flies heterozygous for a wild and a marker chromosome. The Darwinian fitness of homozygotes for each second chromosome relative to the fitness of flies carrying random combinations of the natural chromosomes was then inferred. The estimated loss of fitness on making the natural second chromosomes homozygous was substantial, ranging from 39 to 83 pereent, with an average reduction in fitness of 66 percent.
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PDF | On Dec 1, , Grant Ramsey and others published Darwinian Populations and Natural Selection | Find, read and cite all the research.