Organic Evolution is defined as the sum total of adaptive changes from pre-existing or old form that have taken place over a long time, resulting in diversity of forms, structures and functions among organisms.

<h2>Introduction</h2>
<div class="wp-caption alignnone" style="width: 800px"><img alt=" The photo on the left shows large, stalk-like saguaro cacti with multiple arms, and the photo on the right shows a lizard on a rock." height="273" src="https://data.ulearngo.com/assets/fd9c80dc-7acf-4d1d-85fd-8a5e748299e4" width="800"/><p class="wp-caption-text">All organisms are products of evolution adapted to their environment. (a) Saguaro (<em>Carnegiea gigantea</em>) can soak up 750 liters of water in a single rain storm, enabling these cacti to survive the dry conditions of the Sonora desert in Mexico and the Southwestern United States. (b) The Andean semiaquatic lizard (<em>Potamites montanicola</em>) discovered in Peru in 2010 lives between 1,570 to 2,100 meters in elevation, and, unlike most lizards, is nocturnal and swims. Scientists still do no know how these cold-blood animals are able to move in the cold (10 to 15°C) temperatures of the Andean night. (credit a: modification of work by Gentry George, U.S. Fish and Wildlife Service; credit b: modification of work by Germán Chávez and Diego Vásquez, <em>ZooKeys</em>)</p></div>
<p>All species of living organisms, from bacteria to baboons to blueberries, evolved at some point from a different species. Although it may seem that living things today stay much the same, that is not the case—evolution is an ongoing process.</p>
<p>The <a data-lesson="theory-of-evolution" data-subject="biology" data-tutorial="evolution-overview" href="https://app.ulearngo.com/biology/evolution-overview/theory-of-evolution">theory of evolution</a> is the unifying theory of biology, meaning it is the framework within which biologists ask questions about the living world. Its power is that it provides direction for predictions about living things that are borne out in experiment after experiment. The Ukrainian-born American geneticist Theodosius Dobzhansky famously wrote that “nothing makes sense in biology except in the <a data-lesson="light" data-subject="biology" data-tutorial="sensory-systems" href="https://app.ulearngo.com/biology/sensory-systems/light">light</a> of evolution.” He meant that the tenet that all life has evolved and diversified from a common ancestor is the foundation from which we approach all questions in biology.</p>
<h2 data-type="footnote-refs">Understanding Evolution</h2>
<p>Evolution by <a data-lesson="natural-selection-2" data-subject="biology" data-tutorial="evolution-overview" href="https://app.ulearngo.com/biology/evolution-overview/natural-selection-2">natural selection</a> describes a mechanism for how species change over time. That species change had been suggested and debated well before Darwin began to explore this idea. The view that species were static and unchanging was grounded in the writings of Plato, yet there were also ancient Greeks who expressed evolutionary ideas. In the eighteenth century, ideas about the evolution of animals were reintroduced by the naturalist Georges-Louis Leclerc Comte de Buffon who observed that various geographic regions have different <a data-lesson="summarizing-asexual-reproduction" data-subject="biology" data-tutorial="plant-reproduction" href="https://app.ulearngo.com/biology/plant-reproduction/summarizing-asexual-reproduction">plant</a> and animal populations, even when the environments are similar. It was also accepted that there were extinct species.</p>
<p>During this time, James Hutton, a Scottish naturalist, proposed that geological change occurred gradually by the accumulation of small changes from processes operating like they are today over long periods of time. This contrasted with the predominant view that the geology of the planet was a consequence of catastrophic events occurring during a relatively brief past.</p>
<p>Hutton’s view was popularized in the nineteenth century by the geologist Charles Lyell who became a friend to Darwin. Lyell’s ideas were influential on Darwin’s thinking: Lyell’s notion of the greater age of Earth gave more time for gradual change in species, and the process of change provided an analogy for gradual change in species. In the early nineteenth century, Jean-Baptiste Lamarck published a book that detailed a mechanism for evolutionary change.</p>
<p>This mechanism is now referred to as an inheritance of acquired characteristics by which <a data-lesson="chemical-modifications-protein-activity-and-longevity" data-subject="biology" data-tutorial="gene-expression" href="https://app.ulearngo.com/biology/gene-expression/chemical-modifications-protein-activity-and-longevity">modifications</a> in an individual are caused by its environment, or the use or disuse of a structure during its lifetime, could be inherited by its <a data-lesson="reproduction-methods" data-subject="biology" data-tutorial="reproductive-system" href="https://app.ulearngo.com/biology/reproductive-system/reproduction-methods">offspring</a> and thus bring about change in a species. While this mechanism for evolutionary change was discredited, Lamarck’s ideas were an important influence on evolutionary thought.</p>

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Understanding Evolution

Biology studies life and living organisms. Biology can be divided into different sections that cover the morphology, physiology, anatomy, behavior, and so on of living organisms.

Biology

Learn about the intricacies of evolution, natural selection, speciation, and reproductive isolation to gain a deep understanding of the origin of species.


Understanding Evolution

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