Selection
Selection, commonly referred to as natural selection, is a fundamental mechanism of evolution that explains how species change over time. Proposed by Charles Darwin, the theory posits that within each generation of living organisms, variations exist, some of which may provide advantages in survival and reproduction. Those individuals with favorable traits are more likely to survive and pass on these traits to the next generation, leading to the gradual spread of beneficial variations within a population. Conversely, traits that are less advantageous tend to diminish over time.
Natural selection operates alongside other evolutionary processes and requires a high rate of reproduction and mortality, often taking millions of years for significant changes to manifest. It is observable in various environments, with notable examples including Darwin's studies of finches in the Galápagos Islands and the adaptation of peppered moths in response to industrial pollution in England. While the theory of evolution through natural selection is widely accepted in the scientific community, it remains a topic of controversy for some, particularly in discussions surrounding human origins and various cultural beliefs. This ongoing debate highlights the intersection between scientific inquiry and diverse perspectives on the origins and development of life on Earth.
Selection
Selection, also known as natural selection, is one of the most important factors in evolution, or the process by which the traits of living things change over time. Developed by English naturalist Charles Darwin, the theory of evolutionary selection states that every generation of living things has some degree of variation. These variable factors can make it easier or harder for individuals to survive. Individuals with variations that help them survive will be more likely to reproduce and genetically pass along those special variations to the next generation. The other individuals, with less beneficial variations, will be less likely to reproduce and pass along their traits. Through this process, the most beneficial variations eventually spread widely through the entire population, while less desirable variations slowly disappear. The result of these changes is the evolution of species that has been fundamental to the development of all living things.
Development of the Theory
Charles Darwin developed his theories after years of travel and observation of the natural world. He published his findings in On the Origin of Species in 1859. Since then, scientists have analyzed his work and claims, coming to see them as a unified illustration of the diversity of life and the course of nature.
Natural selection is one of the main tenets of Darwin's evolution theory. However, other important ideas fill out the rest of the proposition, such as that living things are descended from common ancestors. As these living things exist through many generations, changes inevitably occur, due to random mutations or adaptive alterations. Helpful changes are perpetuated through natural selection, while unhelpful changes gradually disappear.
Over a great deal of time, a small change can develop into an entirely new species of living thing. This, Darwinists believe, accounts for the enormous diversity of life on the planet. Even humans are not exempt, and one of the most famous illustrations of Darwinism is the idea that humans evolved from apes. Over millions of years, the theory holds, apes grew taller, their brains developed, and their body forms changed until they had become the humans of modern times.
Many people found this idea distasteful or argued that Darwin's theory was in opposition to various religious teachings about the origins of living things. Darwin's theories thereby gained many critics and detractors. However, over generations of analysis, testing, and reflection, most scientists have accepted Darwin's theories as a comprehensive explanation of how living things develop and change over time. In the twenty-first century, evolution is widely accepted but still considered controversial among some groups.
Process of Natural Selection
Just as natural selection is one factor in the process of evolution, so too are there several factors within the process of natural selection. One factor is variation, the idea that no two living things are exactly the same. In most cases, individuals in a species will have overall similarities but then a large variety of smaller differences. Among humans, variations include height; weight; color of skin, hair, and eyes; speed; strength; intelligence; health; and innumerable other features. Even the tiniest creatures, which may appear at first glance to be identical, all have tiny variations within their species.
These variations come about in many ways, but they are often encoded in DNA, the instructions in living cells that determine development. DNA is passed along to offspring, which is why many children share certain features of their parents. Darwin and his peers in the nineteenth century did not understand the workings of DNA, but later scientific discoveries in genetics identified the importance of DNA in the process.
Variations come into play in many ways in the real world. In nature, creatures must find ways to survive in frequently hostile environments. They must avoid predators, find enough food to eat, and ideally attract mates. Some variations, such as stronger muscles for running, sharper eyesight for finding prey, or coloration that blends into surroundings can all benefit a creature and make it more liable to survive and reproduce. Creatures whose variations make them less adept at survival and reproduction, however, will most likely fail to pass on their DNA, thus bringing an end to their variation.
Natural selection also requires a high rate of reproduction and mortality, and usually a great deal of time. It may take millions of years for one species to adapt to its changing environment or take on enough differences as to make it qualify as an entirely new species.
Examples of Natural Selection
Examples of natural selection may be seen in almost any natural environment. One of the first and most famous examples to be recognized came from Darwin, who studied animal life in the Galápagos Islands during his travels. Darwin observed that finches, a kind of bird native to the islands, had variably shaped beaks. He theorized that the birds experienced a high rate of natural selection because birds with thicker and stronger beaks were able to eat more kinds of seeds during times when food was scarce. Birds with thinner and weaker beaks would not have access to the nourishment and would therefore be less likely to survive and reproduce.
One of the most striking cases of natural selection occurred among moths in England during the 1800s. At that time, factories were becoming increasingly common in cities, and the soot and other air pollution the factories created quickly coated trees and other surfaces with black grime. The peppered moth in England was usually light-colored, with only rare variants having a darker shade. When dark grime coated much of England's cities, light-colored moths became much more visible to birds and other predators and were eaten at a far faster rate than the rarer, dark-colored moths. Over a surprisingly short time—less than a hundred years—light moths had become very rare in cities, and dark moths were common. Although there have been countless millions of examples of natural selection in the world, this remains one of the fastest and clearest illustrations of the process and its profound effects on species.
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