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What is evolution?

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In a Nutshell

Evolution is the biological model for the history of life on Earth.  While some consider evolution to be equivalent to atheism, BioLogos sees evolution as a description of how God created all life.  Evolution refers to descent with modification.  Small modifications occur at the genetic level (in DNA) with each generation, and these genetic changes can affect how the creature interacts with its environment. Over time, accumulation of these genetic changes can alter the characteristics of the whole population, and a new species appears.  Major changes in life forms take place by the same mechanism but over even longer periods of time.  All life today can be traced back to a common ancestor some 3.85 billion years ago.

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In Detail


The word evolution can be used in many ways, but in biology, it means descent with modification. In other words, small modifications occur at the genetic level (i.e. in DNA) when a new generation descends from an ancestral population of individuals within a given species. Over time the modifications fundamentally alter the characteristics of the whole population. When the population accumulates a substantial number of changes and conditions are right, a new species may appear.

Universal Common Descent

A cardinal principle of evolutionary theory is that all living things—including humans—are related to one another through common descent from the earliest form of life, which first appeared on earth about 3.85 billion years ago. How the first simple organisms arose is still a scientific mystery, but we know that they carried hereditary information and were capable of self-replication. Over eons, successive generations led to the marvelous diversity of living things that exist today. Common descent is supported by multiple independent lines of evidence, most notably the fossil record and the comparison of many species’ genomes.

Mechanisms of Evolution

When Charles Darwin published The Origin of Species in 1859, descent with modification was not a particularly new or controversial idea. Darwin’s intellectual leap was to propose the mechanism by which evolution occurred. That mechanism, called natural selection, is a description of what happens when variations occur in a population where resources are limited. When more individuals are born than the environment can support, those with advantageous variations are more likely to survive than those without them. This differential reproduction leads to overall changes in the traits of a population over time.

Natural selection is called “natural” not because it occurs apart from God’s activity (after all, many believe natural laws and processes are a reflection of God’s activity), but because it is the usual pattern one observes in nature, in contrast to the “artificial” selection practiced for centuries by farmers and animal breeders.

Other mechanisms of evolution besides natural selection include sexual selection and genetic drift. Sexual selection occurs when individuals of one sex are attracted to mates which manifest certain traits (the peacock’s tail arose this way, for example). Genetic drift is the random (i.e. unpredictable) fluctuations that naturally occur in a population’s gene pool when the population is small. The best adapted individuals do not always survive to reproduce, while poorly adapted individuals don’t always die before passing on their genes. Over time, in small populations, genetic drift can lead to noticeable change.

More recently, it has been proposed that a group of organisms could sometimes benefit from its members behaving in ways that would otherwise be detrimental to an individual organism. This so-called group selection takes into account the survival needs of an entire community of a given species.

Genetic Mutations as the Source of Variation

Darwin recognized from his years of study that when any organism reproduces, new variants sometimes arise. Although he didn’t know it at the time, these differences were a consequence of mutations. Mutations are changes in DNA that occur due to errors in DNA replication or exposures to radiation or certain chemicals. The vast majority of mutations are neutral or harmful and are not preserved, but occasionally beneficial mutations occur that are preferentially passed down through the generations.


A number of common misconceptions have led to confusion or suspicion about evolution over the years. One common argument is that despite hundreds of years of observation, there has been no experimental proof of one species evolving from another, such as a cat turning into a dog. The truth is, such a drastic transition is not predicted by the theory of evolution. In some cases, scientists have observed speciation, but it is true that we have not observed major changes in form. The reason, is that we simply haven’t been watching long enough.1 Evolution of new forms—what some people call “macroevolution”—takes a very, very long time.

Next, the claim that humans share common ancestry with other species should not be misunderstood to mean that humans have evolved from any other presently existing species. Humans do share close common ancestry with other living primates, but rather than being direct descendants, we are more like cousins. Other primates have been changing as well over the past 5-6 million years since humans and chimpanzees diverged from a common ancestor.

A third misconception is that evolution is a random, purposeless process. It is true that individual mutations are random, in the sense that they are unpredictable, but natural selection is decidedly non-random. Whether there is any purpose behind the evolutionary process is not a scientific question, and the answer depends greatly on one’s worldview. For believers in the God of the Bible who created and sustains the whole universe, evolution is simply the means by which he accomplishes his praiseworthy purposes of bringing forth life.

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Next: What does the fossil record show?

Further Reading

Web sites






  • Alexander, Denis. Creation or Evolution: Do We Have to Choose? Oxford: Monarch Books, 2008.
  • Collins, Francis S. The Language of God: A Scientist Presents Evidence for Belief. New York: Free Press, 2006.
  • Darwin, C. R. On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life. London: John Murray, 1859.
  • Falk, Darrel R. Coming to Peace with Science: Bridging the Worlds between Faith and Biology. Downers Grove, IL: InterVarsity Press, 2004.
  • Giberson, Karl. Saving Darwin: How to be a Christian and Believe in Evolution. New York: HarperOne, 2008.
  • Miller, Kenneth. Finding Darwin’s God: A Scientist’s Search for Common Ground Between God and Evolution. New York: Cliff Street Books, 1999.
  • Weiner, Jonathan The Beak of the Finch: A Story of Evolution In Our Time. New York: Knopf, 1994.



  1. Darrel Falk, Coming to Peace with Science, 131.