![]() So natural selection may not produce perfection, but you’d at least expect it to get rid of obviously deleterious genes, wouldn’t you? Maybe not…. In this case, perhaps no net increase in fitness would result from the faster alleles. Although longer limb bones increase stride, their chances of failing due to bending loads increases as well. Perhaps faster alleles exist in the cheetah population - but there is a trade-off associated with them: the alleles produce cheetahs with longer legs (and hence more speed), but these long legs are hazardously delicate. There really may be “no way to get there from here.”Ĭhanging one feature for the better might change another for the worse. Perhaps a different arrangement of leg muscles and bones would produce cheetahs that run faster - however, the basic body form of mammals is already laid out in their genes and development in such a mutually constrained way, that it is unlikely to be altered. A cheetah might run faster if it had “faster” alleles - but if faster alleles are not in the population from mutation or gene flow, evolution in this direction will not happen. Selection can only operate on the available genetic variation. The CIA World Factbook gives the world annual birthrate, mortality rate, and growth rate as 1.89, 0.79, and 1.096 respectively. In 2009, the estimated annual growth rate was 1.1. Here are a few reasons why natural selection might not produce perfection or faster cheetahs: Globally, the growth rate of the human population has been declining since 19, when it was 2.20 per annum. For example, you might imagine that cheetahs could catch more prey and produce more offspring if they could run just a little faster. There are many reasons why natural selection may not produce a “perfectly-engineered” trait. Information on controversies in the public arena relating to evolution.(c) Many of the points in dotplot A fall outside of the interval from 0.30 to 0.40, so it is not at all surprising for a sample proportion based on n 20 to be more than 0.05 from the population proportion. Alignment with the Next Generation Science Standards points in dotplot C are more than 0.10 away from p 0.35, so it would be extremely unlikely to be that far o when n 500.The big issues – Pacing, diversity, complexity, and trends.Macroevolution – Evolution above the species level.Microevolution – Evolution within a population.Mechanisms: the processes of evolution – Selection, mutation, migration, and more.The history of life: looking at the patterns – Change over time and shared ancestors.An introduction to evolution: what is evolution and how does it work?. ![]()
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