Why does evolution take place

Evolution occurs when these heritable differences become more common or rare in a population, either non-randomly through natural selection or randomly through genetic drift. Natural selection is a process that causes heritable traits that are helpful for survival and reproduction to become more common, and harmful traits to become more rare. This occurs because organisms with advantageous traits pass on more copies of these heritable traits to the next generation.

Over many generations, adaptations occur through a combination of successive, small, random changes in traits, and natural selection of those variants best-suited for their environment.

Genetic drift arises from the role chance plays in whether a given individual will survive and reproduce. One definition of a species is a group of organisms that can reproduce with one another and produce fertile offspring.

However, when a species is separated into populations that are prevented from interbreeding, mutations, genetic drift, and the selection of novel traits cause the accumulation of differences over generations and the emergence of new species. The similarities between organisms suggest that all known species are descended from a common ancestor or ancestral gene pool through this process of gradual divergence. The theory of evolution by natural selection was proposed roughly simultaneously by both Charles Darwin and Alfred Russel Wallace, and set out in detail in Darwin's book On the Origin of Species.

In the s, Darwinian natural selection was combined with Mendelian inheritance to form the modern evolutionary synthesis, in which the connection between the units of evolution genes and the mechanism of evolution natural selection was made. This powerful explanatory and predictive theory has become the central organizing principle of modern biology, providing a unifying explanation for the diversity of life on Earth.

Survival of the fittest usually makes one think of the biggest, strongest, or smartest individuals being the winners, but in a biological sense, evolutionary fitness refers to the ability to survive and reproduce in a particular environment. Popular interpretations of "survival of the fittest" typically ignore the importance of both reproduction and cooperation.

To survive but not pass on one's genes to the next generation is to be biologically unfit. And many organisms are the "fittest" because they cooperate with other organisms, rather than competing with them. Learn More Adaptation and Natural Selection. In the process of natural selection, individuals in a population who are well-adapted to a particular set of environmental conditions have an advantage over those who are not so well adapted.

The advantage comes in the form of survival and reproductive success. For example, those individuals who are better able to find and use a food resource will, on average, live longer and produce more offspring than those who are less successful at finding food.

Inherited traits that increase individuals' fitness are then passed to their offspring, thus giving the offspring the same advantages. Individual organisms don't evolve. Populations evolve. Because individuals in a population vary, some in the population are better able to survive and reproduce given a particular set of environmental conditions. These individuals generally survive and produce more offspring, thus passing their advantageous traits on to the next generation.

Over time, the population changes. Learn More Sex and the Single Guppy. Many people, from evolutionary biologists to important religious figures like Pope John Paul II, contend that the time-tested theory of evolution does not refute the presence of God.

They acknowledge that evolution is the description of a process that governs the development of life on Earth. Like other scientific theories, including Copernican theory, atomic theory, and the germ theory of disease, evolution deals only with objects, events, and processes in the material world.

Science has nothing to say one way or the other about the existence of God or about people's spiritual beliefs. Learn More Science and Faith. Web Activities. About the Project. Site Map. Similarly, the use of pesticides in agriculture has driven the evolution of resistant insects that require more or harsher chemicals to be killed. Scientists studying Galapagos finches have seen evolutionary changes in beak size and shape in just a few years.

Major evolutionary transformations take much, much longer. Learn More Microbe Clock. Earth is approximately 4. Radiometric dating, a method that measures the level of radioactive decay in rocks to determine how old they are has consistently aged moon rocks and meteorites at 4.

Ages of these types of rocks provide the most accurate estimates of the age of Earth and the rest of the solar system because they have not been subjected to the same forces that recycle Earth's crust. As new land forms along cracks between the planet's continental plates, old rocks are destroyed. Thus, the oldest rocks on Earth may not exist anymore. The oldest dated minerals, at 4. Learn More Evidence for Evolution. The oldest known fossils are approximately 3.