Natural Selection and Adaptation Natural selection can be
Natural Selection and Adaptation Natural selection: can be defined as the sum total of environmental forces or pressures that determine fitness. Malthus – perils of overpopulation – geometric increase Darwin – elephants - Individuals best suited to the environment will be the ones that manage to survive and reproduce - Variation under domestication – artificial selection Natural selection – the analogue to artificial selection. 1. Competition for finite resources and harsh physical realities 2. Limitations on those who reproduce 3. Result: preferential survival and
Adaptation is a noncreationist explanation of the apparent design in nature. Adaptation results from a change in form through time which reflects changing adaptations resulting from natural selection. With natural selection, not all individuals contribute equal numbers of offspring to the next generation. Traits that enhance survival and reproduction will tend to increase in frequency from generation to generation. Such traits are adaptive which makes those who carry them more “fit. ”
Genetics and evolution Darwin: Natural selection operated on individuals and fitness also applied to individuals. However, genetics was not part of Darwin’s thinking. Modern evolutionary biologists think of natural selection as favoring or discouraging particular traits. Mendel: demonstrated that inheritance was not a blending process, as Darwin believed. Mendel demonstrated that inheritance involved discrete units or particles (which we now call genes) which retain their integrity from generation to generation. genotype: the complete set of genes an individual possesses phenotype: all observable traits of an individual’s appearance and behavior
Genetics an evolution Gene pool – the complete set of genes that characterizes a species or breeding population. Evolution: Darwin - “descent with modification” today - change through time in allele frequencies in a population. Population: a group of organisms in the same species that regularly breed together
Evolutionary forces How does the gene pool change? 1. The simplest change – the adding of new genetic material or gene. 2. The majority of gene pool changes are not the result of adding new genes but are instead the result of changing frequencies of genes already present. The actual course that evolutionary changes takes depends on 2 things: • Partly on the genes already present in the gene pool – I. e. , evolution is opportunistic • Partly on the cause of the gene pool change. Forces that cause change in the gene pool: mutation, natural selection, migration, and “accidents of sampling” (random genetic drift, the Founder effect, the “bottleneck” effect).
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