Natural Selection




The Scientific Theory of Natural Selection

The first successful scientific explanation for the diversity and structure of the natural world was formulated by Charles Darwin and his contemporary, Alfred Russel Wallace. Darwin formulated the basic principle of the Theory of Natural Selection after he began examining the extensive biological and geological samples he collected while on a five year voyage around the world (1831-1836). He, like all scientists, was heavily influenced by the leading minds of his day; however, unlike most of his contemporary biologists and geologists, Darwin had access to an extreme amount of data from diverse locations across the globe. Wallace, inspired by Darwin's voyage, took his own trip around the world and independently came to many of the same hypotheses.

Darwin worked on his scientific work, "On the Origin of Species," for nearly 20 years. It was published in 1859, and he might have worked on it longer if Wallace had not sent him a paper wherein he had himself drawn many of the same conclusions as Darwin. Wallace and Darwin's ideas were presented jointly in 1858 at a meeting of the Linnean Society, but their work received little attention from the community until the publication of Darwin's book.

The Theory of Natural Selection explains the diversity of life on Earth using a few key principles:

  • Species, faced with a selection pressure from their environment, can either adapt or be threatened, possibly with extinction if they are completely unable to adapt. That pressure may be due to a predator or predators, or due to alterations in the climate.
  • Adaptation to a selection pressure can happen due to the use of a preexisting biological trait, or when a sub-population of the species possesses a favorable trait that confers an advantage in survival. This sub-population is more likely to survive and pass along the trait to its children.
  • Over time, those members of the original population which are more successful in the face of selection pressure may form their own new population, expressing commonly the trait(s) that conferred survival. This can result in the formation of a new species.
  • New species descend, with modification, from old species.

There is a non-random and a random component to Natural Selection. Selection pressure is non-random (e.g. predators want to eat prey), and adaptation is non-random (e.g. prey will attempt to avoid predators). The random component has to do with the development of favorable biological traits. Random mutations during cell division at the beginning of life may cause a new trait to be expressed in a child; if the trait allows for an advantage in the face of the selection pressure, the child may live to pass that genetic trait onto its children. Mutation is the random part, but adaptation and selection pressure are the non-random parts.

It is a mis-conception that the Theory of Natural Selection says that life's diversity is random. It is not.

Natural Selection is a scientific theory because is is based on hypotheses drawn from many observations of the natural world; those hypotheses lead to tests that can be used to generate new knowledge, or refute the hypotheses should the tests fail.

Here are examples of how Natural Selection is falsifiable:

  • Natural Selection requires a lot of time to generate the diversity we see on Earth now. If the Earth is younger than a few million years, Natural Selection might be the wrong explanation. The Earth can and has been independently dates using methods on samples both from Earth and the Moon, and has been found to be about 4.54 billion years old, give or take about 0.05 billion years.
  • Natural Selection predicts that all species on Earth seen now should have descended from earlier species; if we find a species on Earth whose genetic code is nothing like any other species, then Natural Selection might be wrong.
  • If a fossil from one geological era is found mixed in with fossils from a different geological era, and dates back to that era, then Natural Selection could be wrong. For instance, if a human skeleton is found in the mouth of a Tyrannosaurus Rex skeleton, Natural Selection might be wrong since these two species lived nowhere near one another in time.
There are many other examples of falsifiability; these are just a few.

Media on the Theory of Natural Selection

The Howard Hughes Medical Institute, with the help of University of Wisconsin-Madison biologist Sean B. Carroll, have produced some beautiful short films illustrating the principles of Natural Selection working in our world. These films are great learning and teaching tools and help dispel common myths, misunderstandings, and utter falsifications regarding Natural Selection.

All of the films are available from: http://www.hhmi.org/biointeractive/shortfilms/

Here are some excellent books that relate aspects of the Theory of Natural Selection in an easy-to-understand way, for different levels of reader:

Here are books that can help people of faith reconcile religion and science, written by scientists who are also people of faith.

Lecture Video and Audio