There are many misconceptions about evolution, including the meaning of the word theory, the way populations change, and the origin of life.
Discuss misconceptions about the theory of evolution
Attacks on the theory of evolution sometimes take issue with the word "theory", which in the vernacular means a guess or suggested explanation. In scientific language, "theory" indicates a body of thoroughly-tested and verified explanations for a set of observations of the natural world.
Evolution does not take place on an individual level; evolution is the average change of a characteristic within an entire population.
Evolution does not explain the origin of life; the theory of evolution instead explains how populations change over time and how traits are selected in order to increase the fitness of a population.
Favorable traits do not arise as a result of the environment as these traits are already present; individuals with favorable traits are more likely to survive and, thus, will have greater fitness than individuals with less desirable traits.
Evolution and natural selection are not synonymous. Natural selection is just one mechanism by which evolution occurs.
a well-substantiated explanation of some aspect of the natural world based on knowledge that has been repeatedly confirmed through observation and experimentation
Lamarckian inheritance is the idea that an organism can pass on characteristics that it acquired during its lifetime to its offspring (also known as heritability of acquired characteristics or soft inheritance). It is named after the French biologist Jean-Baptiste Lamarck (1744–1829), who incorporated the action of soft inheritance into his evolutionary theories. Mendelian genetics supplanted the notion of inheritance of acquired traits, eventually leading to the development of the modern evolutionary synthesis and the general abandonment of the Lamarckian theory of evolution in biology. Despite this abandonment, interest in Lamarckism has continued as studies in the field of epigenetics have highlighted the possible inheritance of behavioral traits acquired by the previous generation.
Misconceptions of Evolution
Although the theory of evolution generated controversy when it was first proposed, it was almost universally accepted by biologists within 20 years of the publication of On the Origin of Species. Nevertheless, the theory of evolution is a difficult concept and misconceptions about it abound.
Evolution is Just a Theory
Critics of the theory of evolution dismiss its importance by purposefully confounding the everyday usage of the word "theory" with the way scientists use the word. In science, a "theory" is understood to be a body of thoroughly-tested and verified explanations for a set of observations of the natural world. Scientists have a theory of the atom, a theory of gravity, and the theory of relativity, each of which describes understood facts about the world. In the same way, the theory of evolution describes facts about the living world. A theory in science has also survived significant efforts to discredit it by scientists. In contrast, a "theory" in common vernacular is a word meaning a guess or suggested explanation; this meaning is more akin to the scientific concept of "hypothesis. " When critics of evolution say evolution is "just a theory," they are implying that there is little evidence supporting it and that it is still in the process of being rigorously tested. This is a mis-characterization.
Evolution is the change in genetic composition of a population over time, specifically over generations, resulting from differential reproduction of individuals with certain alleles. Individuals do change over their lifetime, obviously, but this is called development and involves changes programmed by the set of genes the individual acquired at birth in coordination with the individual's environment. When thinking about the evolution of a characteristic, it is probably best to think about the change of the average value of the characteristic in the population over time. For example, when natural selection leads to bill-size change in medium-ground finches in the Galápagos, this does not mean that individual bills on the finches are changing. If one measures the average bill size among all individuals in the population at one time and then measures the average bill size in that population several years later, this average value of the population will be different as a result of evolution.
Evolution Explains the Origin of Life
It is a common misunderstanding that evolution includes an explanation of life's origins. The theory of evolution explains how populations change over time. It does not shed light on the beginnings of life, including the origins of the first cells, which is how life is defined. The mechanisms of the origin of life on earth are a particularly difficult problem because it occurred a very long time ago and, presumably, it occurred just once. However, while evolution does not explain the origin of life, it may have something to say about some of the processes operating once pre-living entities acquired certain properties. Once a mechanism of inheritance was in place in the form of a molecule like DNA, either within a cell or pre-cell, these entities would be subject to the principle of natural selection. More effective reproducers would increase in frequency at the expense of inefficient reproducers.
Organisms Evolve on Purpose
Statements such as "organisms evolve in response to a change in an environment" may lead to the misunderstanding that evolution is somehow intentional. A changed environment results in some individuals in the population, those with particular phenotypes, benefiting and, therefore, producing proportionately more offspring than other phenotypes. This results in change in the population if the characteristics are genetically determined.
It is important to understand that the variation that natural selection works on is already present in a population and does not arise in response to an environmental change. For example, applying antibiotics to a population of bacteria will, over time, select a population of bacteria that are resistant to antibiotics. The resistance, which is caused by a gene, did not arise by mutation because of the application of the antibiotic. The gene for resistance was already present in the gene pool of the bacteria, probably at a low frequency. The antibiotic, which kills the bacterial cells without the resistance gene, strongly selects individuals that are resistant, since these would be the only ones that survived and divided. Experiments have demonstrated that mutations for antibiotic resistance do not arise as a result of antibiotics.
In a larger sense, evolution is not goal directed. Species do not become "better" over time; they track their changing environment with adaptations that maximize their reproduction. The characteristics that evolve in a species are a function of preexisting variation and the environment, both of which are constantly changing non-directionally. A trait that is fit in one environment at one time may also be fatal at some point in the future.
Evolution = Natural Selection
The terms “evolution” and “natural selection” are often conflated, as the two concepts are closely related. They are not, however, synonymous. Natural selection refers to the process by which organisms better suited for their environment are more likely to survive and produce offspring, thereby proliferating those favorable genetics in a population. Evolution is defined more broadly as any change in the genetic makeup of a population over time. As expounded by Darwin, natural selection is a major driving force of evolution, but it is not the only one.
Genetic drift, for example, is another mechanism by which evolution may occurs. Genetic drift occurs when allelic frequency is altered due to random sampling. It is evolution by chance, and the smaller the population, the more significant the effects on genetic distribution due to sampling error. For example, a population bottleneck, which occurs when an event such as a natural disaster dramatically reduces the size of a population, can result in the elimination or significant reduction of a trait within a population, regardless of how beneficial that trait may be to survival or reproduction. Thus evolution can occur without natural selection.