Natural Selection (Industrial melanism)

Natural Selection (Industrial melanism) Natural selection can be explained clearly through industrial melanism. Industrial melanism is a classical case of Natural selection exhibited by the peppered moth, Biston betularia . These were available in two forms, white winged and black winged. Before industrialization peppered moth both white and black coloured were common in England. Pre-industrialization witnessed more white winged moths than dark winged moths because of the dense growth of white coloured lichens on trees. They escaped from predators due to the white background. Post-industrialization caused the tree trunks became dark due to smoke and soot let out from the industries. The lichen population also decreased because they could not grow in polluted areas. The white winged moths were easily identified by their predators as the background turned black due to soot and smoke while the black winged moths camouflaged with the dark background. Hence the dark coloured moth population was selected and their number increased when compared to the white moths. Nature offered positive XII Std Zoology Chapter XII Std Zoology Chapter Evolution that time, Darwin's finches have evolved into recognized species differing in body size, beak shape and feeding behavior. Changes in the size and form of the beak have enabled different species to utilize different food resources such as insects, seeds, nectar from cactus flowers and blood from iguanas, all driven by Natural selection. Fig. . represents some of the finches observed by Darwin. Genetic variation in the ALX1 gene in the DNA of Darwin finches is associated with variation in the beak shape. Mild mutation in the ALX1 gene leads to phenotypic change in the shape of the beak of the Darwin finches. Marsupials in Australia and placental mammals in North America are two subclasses of mammals they have adapted in similar way to a particular food resource, locomotory skill or climate. They were separated from the common ancestor more than million year ago and each lineage continued to evolve independently. Despite temporal and geographical separation, marsupials in Australia and placental mammals in North America have produced varieties of species living in similar habitats with similar ways of life. Their overall resemblance in shape, locomotory mode, feeding and foraging are superimposed upon different modes of reproduction. This feature reflects their distinctive evolutionary relationships. Over species of marsupials live in Australia along with many fewer species of placental mammals. The marsupials have undergone adaptive radiation to occupy the diverse habitats in Australia, just as the placental mammals have radiated across North America. selection pressure to the black coloured moths. The above proof shows that in a population, organisms that can adapt will survive and produce more progenies resulting in increase in population through natural selection. Artificial selection is a byproduct of human exploitation of forests, oceans and fisheries or the use of pesticides, herbicides or drugs. For hundreds of years humans have selected various types of dogs, all of which are variants of the single species of dog. If human beings can produce new varieties in short period, then “nature” with its vast resources and long duration can easily produce new species by selection.