What is Evolution?
In a general sense, evolution means “change through time.” This concept has been broadly applied not only to biology, but also in the fields of geology, astronomy, economics and history.
Biological evolution, as understood today refers to cumulative changes in gene frequency that occur within populations through time. Over time, inherited genetic changes in populations can produce entirely new species. The central idea of biological evolution is that all life on Earth shares a common ancestor.
The modern understanding of biological evolution begins with the publication of Charles Darwin’s book On the Origin of Species(1859). Darwin himself offered one of the best definitions of evolution, simply stated as “descent with modification.” Because of this book, Darwin stands at the center of one of the great intellectual revolutions in human history.
How long does evolution take?
Evolution takes place on different time scales. Scientists refer to evolutionary changes over short time scales, such as one generation, as microevolution. These changes take place within a population or group of interbreeding organisms. Examples of microevolution include insects that become resistant to pesticides, bacterial strains that evolve resistance to antibiotics, and trends in bird body sizes across regions.
In contrast, macroevolution operates over much longer time scales and involves major evolutionary transformations that result in the appearance of new evolutionary lineages. Examples of macroevolution include the evolution of amphibians from fish. Macroevolution is the cumulative effect of microevolution. Another way to express the difference is that macroevolution is between-species evolution and microevolution is within-species evolution.
Can evolution really be responsible for amazingly complex biological features, such as the human eye?
Yes. Evolution can produce extremely complex structures. Darwin reasoned that “if numerous gradations from a simple and imperfect eye to one complex and perfect can be shown to exist” then he felt complex structures like the eye could evolve.
It is thought that a simple light-sensitive spot on the skin of an ancestral animal conferred a slight evolutionary advantage to escape predators or find food. These successful organisms were favored to survive and passed their genes to the next generation. Over millions of years, accumulated random genetic changes and natural selection eventually produced a complex eye.
Because complex eyes have developed separately in a number of different animal groups, some have claimed that this cannot easily be explained by natural selection. One dramatic recent finding in molecular genetics is that there is a common set of genes involved in the early development of anatomically complex eyes of all animals, thus providing a basis for natural selection in independent lineages.
 Return to Top of Page
Is evolution a fact, theory, or hypothesis?
Evolution is a scientific theory. A scientific theory is one that can be tested by gathering evidence that either disproves or supports it. Facts support or refute theory. Some theories (e.g., relativity and gravity) are so well supported that we think of them as fact, and for most scientists, evolution is in that category.
Sometimes confusion results in the misunderstanding of the differences between scientific terms such as theory, hypothesis, and fact. To help clarify their meanings:
A hypothesis is a proposed explanation for a phenomenon. Hypotheses are the first step in the formation of a theory. If a hypothesis is confirmed through experimental testing, observation, and data collection, it can become a theory. Many hypotheses fail these tests and have to be revised or completely rejected. This testing and error-correcting behavior is the basic feature of science and serves to advance and improve the current state of scientific knowledge.
A scientific theory is an explanation of some aspect of the natural world that is well substantiated by evidence. Scientific theories provide interpretations of the natural world that are supported by experimentation and observation. Take gravity and electricity, for example. These two phenomena are explained by theories that each one of us test and observe everyday.
Examples of scientific theories include relativity and gravitation. Powerful theories like evolution have stood the test of time—weathering the challenges of new discoveries and standing up to intense scrutiny by the scientific community. Evolution is a scientific theory that unifies all aspects of the biological sciences and provides a framework to understand the history of life on Earth.
Facts are knowledge or information based on real occurrences that have been directly observed. Facts support or refute theories.
Return to Top of Page
Does accepting evolution preclude having religious beliefs?
No. The methodology of science is the most effective means of describing how the natural world works. It has given humankind the automobile, airplane, computer, medicine, and agriculture—all the technologies that sustain our modern society. There is no other system that works as well to describe the world around us.
In contrast, religion is a faith-based belief system. For many people, it offers guidance and provides comfort and meaning to their lives. Science and religion are not mutually exclusive. Many scientists are religious, and some scientists feel that knowledge of the natural world complements their religious beliefs.
(Courtesy: Field Museum, Chicago)
![]()
|
