- The process of evolution
evolution
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What is evolution?
Evolution is the process by which living organisms change and diversify over time. This change affects all aspects of life, including morphology, physiology, behavior, and ecology, driven by alterations in hereditary materials. The core mechanism of evolution is natural selection, where favorable hereditary variations increase an organism's chances of survival and reproduction, leading to adaptation to its environment. Evidence for evolution comes from the fossil record, comparative anatomy, and molecular biology, particularly the study of DNA. Molecular biology has revealed a fundamental unity among all living organisms, indicating common ancestry.
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Who first explained the theory of evolution?
The theory of evolution by natural selection was first explained by Charles Darwin. While Alfred Russel Wallace also independently postulated the theory of evolution by natural selection, Darwin's extensive observations during his voyage on the HMS Beagle provided crucial evidence. Darwin published his seminal work, On the Origin of Species, in 1859, detailing his theory that organisms evolve over time through natural selection, where variations that enhance survival and reproduction are passed on to offspring. This revolutionary concept challenged existing beliefs and laid the foundation for modern evolutionary studies.
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How does natural selection work in evolution?
Natural selection is the process by which organisms adapt to their environment through the selective reproduction of advantageous genetic traits. Variations that enhance an organism's survival and ability to reproduce are preserved and passed on to future generations, while less advantageous variations diminish. This differential reproduction can occur due to differences in survival rates, fertility, mating success, or other life cycle aspects.
While random processes like mutation, migration, and genetic drift can alter gene frequencies, natural selection acts as a moderating force. It promotes beneficial mutations and eliminates harmful ones, leading to populations that are better adjusted to their surroundings. This process is fundamental to evolution, driving changes in morphology, physiology, behavior, and ecology over time.
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What evidence do scientists use to support evolution?
Scientists use a variety of evidence to support the theory of evolution. This includes the study of fossils, which reveal the history of life on Earth and show progressive changes in organisms over time. Comparative anatomy highlights structural similarities, known as homologies, between different species that suggest a common ancestor, even if the structures serve different functions today. Furthermore, molecular biology provides compelling evidence through the study of DNA and proteins. The remarkable uniformity in the genetic code and the sequences of DNA and proteins across diverse organisms strongly indicates a shared ancestry. The degree of similarity in these molecules directly correlates with the recency of common ancestry, allowing scientists to reconstruct evolutionary relationships.
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How do mutations contribute to evolution?
Mutations are permanent alterations in an organism's genetic material that introduce new genetic variations. These variations are the raw material for evolution. Mutations can arise spontaneously or be induced by environmental factors like radiation or chemicals.
When mutations occur in reproductive cells (germinal mutations), they can be passed on to offspring, introducing new traits into a population. While many mutations are neutral or harmful, some can be beneficial, improving an organism's ability to survive and reproduce in its environment. Natural selection then favors these advantageous mutations, causing them to increase in frequency over generations, driving the evolutionary process. This continuous introduction of variation and subsequent selection allows species to adapt to changing environments.
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How has the theory of evolution changed over time with new scientific discoveries?
The theory of evolution has been significantly refined and expanded with new scientific discoveries. Initially proposed by Charles Darwin and Alfred Russel Wallace based on observations of variation and natural selection, the theory lacked understanding of the fundamental unit of heredity.
The 20th century brought advancements in genetics, revealing the role of genes and DNA in inheritance. This allowed for a more detailed understanding of how evolutionary changes occur at the population level, known as microevolution. New techniques in dating and molecular biology have further strengthened evolutionary evidence, enabling scientists to reconstruct evolutionary history with unprecedented detail. Discoveries in comparative anatomy and the fossil record also provide ongoing support and insights into evolutionary processes.
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News •
evolution, theory in biology postulating that the various types of plants, animals, and other living things on Earth have their origin in other preexisting types and that the distinguishable differences are due to modifications in successive generations. The theory of evolution is one of the fundamental keystones of modern biological theory.
The diversity of the living world is staggering. More than 2 million existing species of organisms have been named and described; many more remain to be discovered—from 10 million to 30 million, according to some estimates. What is impressive is not just the numbers but also the incredible heterogeneity in size, shape, and way of life—from lowly bacteria, measuring less than a thousandth of a millimetre in diameter, to stately sequoias, rising 100 metres (300 feet) above the ground and weighing several thousand tons; from bacteria living in hot springs at temperatures near the boiling point of water to fungi and algae thriving on the ice masses of Antarctica and in saline pools at −23 °C (−9 °F); and from giant tube worms discovered living near hydrothermal vents on the dark ocean floor to spiders and larkspur plants existing on the slopes of Mount Everest more than 6,000 metres (19,700 feet) above sea level.
The virtually infinite variations on life are the fruit of the evolutionary process. All living creatures are related by descent from common ancestors. Humans and other mammals descend from shrewlike creatures that lived more than 150 million years ago; mammals, birds, reptiles, amphibians, and fishes share as ancestors aquatic worms that lived 600 million years ago; and all plants and animals derive from bacteria-like microorganisms that originated more than 3 billion years ago. Biological evolution is a process of descent with modification. Lineages of organisms change through generations; diversity arises because the lineages that descend from common ancestors diverge through time.
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The 19th-century English naturalist Charles Darwin argued that organisms come about by evolution, and he provided a scientific explanation, essentially correct but incomplete, of how evolution occurs and why it is that organisms have features—such as wings, eyes, and kidneys—clearly structured to serve specific functions. Natural selection was the fundamental concept in his explanation. Natural selection occurs because individuals having more-useful traits, such as more-acute vision or swifter legs, survive better and produce more progeny than individuals with less-favourable traits. Genetics, a science born in the 20th century, reveals in detail how natural selection works and led to the development of the modern theory of evolution. Beginning in the 1960s, a related scientific discipline, molecular biology, enormously advanced knowledge of biological evolution and made it possible to investigate detailed problems that had seemed completely out of reach only a short time previously—for example, how similar the genes of humans and chimpanzees might be (they differ in about 1–2 percent of the units that make up the genes).
This article discusses evolution as it applies generally to living things. For a discussion of human evolution, see the article human evolution. For a more complete treatment of a discipline that has proved essential to the study of evolution, see the articles genetics, human and heredity. Specific aspects of evolution are discussed in the articles coloration and mimicry. Applications of evolutionary theory to plant and animal breeding are discussed in the articles plant breeding and animal breeding. An overview of the evolution of life as a major characteristic of Earth’s history is given in community ecology: Evolution of the biosphere. A detailed discussion of the life and thought of Charles Darwin is found in the article Darwin, Charles.
General overview
The evidence for evolution
Darwin and other 19th-century biologists found compelling evidence for biological evolution in the comparative study of living organisms, in their geographic distribution, and in the fossil remains of extinct organisms. Since Darwin’s time, the evidence from these sources has become considerably stronger and more comprehensive, while biological disciplines that emerged more recently—genetics, biochemistry, physiology, ecology, animal behaviour (ethology), and especially molecular biology—have supplied powerful additional evidence and detailed confirmation. The amount of information about evolutionary history stored in the DNA and proteins of living things is virtually unlimited; scientists can reconstruct any detail of the evolutionary history of life by investing sufficient time and laboratory resources.
Evolutionists no longer are concerned with obtaining evidence to support the fact of evolution but rather are concerned with what sorts of knowledge can be obtained from different sources of evidence. The following sections identify the most productive of these sources and illustrate the types of information they have provided.
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