The nature of biological evolution and the development of evolutionary theory (from core concepts to applications in various fields)

This blog post explains the core concepts of biological evolution and evolutionary theory, covering key mechanisms such as natural selection and gene drift, as well as the impact of evolutionary theory on various disciplines beyond biology and the latest research trends.

 

People often hear the word “evolution” in broadcast media, cartoons, and movies, but they often don’t know what it is. Biological evolution is the phenomenon of living things changing over time, and the theory that explains this process is the theory of evolution. Evolutionary theory has evolved over time to become one of the most central frameworks of biology, and it has become increasingly important as it influences many other scientific disciplines, the humanities, and philosophy. In this article, we’ll take a look at some of the key concepts and developments in evolutionary theory and how it has influenced other fields.
Strictly speaking, evolution, as defined by biology, is “the gradual change in the frequency and proportion of genes within a population of organisms over generations. There is a myriad of evidence that evolution has occurred, whether it’s observing how certain organisms have changed by identifying when fossils were created, or analyzing how species with the same ancestor have changed into different forms as they inhabit different locations. However, the causes and mechanisms by which evolution occurs are still being studied in various directions. The most widely recognized mechanisms are natural selection and gene drift.
Natural selection is the theory that individuals with traits that are better suited to an external environment have an advantage in survival and reproduction over others that are not, and that traits eventually become dominant, and is now accepted as a proven fact rather than a theory. In order for natural selection to occur, individuals must go through the reproductive process of passing on their genes to their offspring, and there must be a trigger that causes them to have a different trait. This is usually a change in the genes themselves, usually by mutation. In many cases, mutations are harmful to the organism, but since the gene does not disappear over the generations, if a slightly favorable mutation occurs, natural selection will pass it on to more children. Individuals with different traits compete with each other for survival, and in the end, those that are better adapted to their environment and leave more offspring survive.
There are three main types of natural selection in a population. The first is directional selection, which occurs when the external environment exerts evolutionary pressure on a group of organisms in one direction. The second is divisive selection, which refers to evolutionary processes in which distinct opposing traits are polarized over generations. The third is stability selection, which is the opposite of divisive selection: the evolution of a population in which traits in the middle of the spectrum become dominant and traits at the extremes become less and less common. Fish called African cichlids are a prime example of directional selection. These fish are a favorite for evolutionary research because they evolve so quickly, and studies analyzing species with different oral structures and their respective diets have shown the effects of directional selection.
Many early evolutionists, including Darwin, considered the selection of traits through mating to be a major component of natural selection. In general, females are more costly to reproduce and raise than males, resulting in the phenomenon of “sexual selection,” in which females select suitable males. Initially conceived to explain the necessity of sex, or the advantages of sexual reproduction over asexual reproduction, sexual selection was long dismissed as a women’s rights issue, but in modern times it has been studied in a variety of ways. One such example is the “red queen hypothesis,” which states that organisms don’t evolve simply to reproduce a lot (asexual reproduction), but seek diversity (sexual reproduction) to survive in a changing environment and competing species. An example of this hypothesis is the mutually competitive evolution of parasites and higher organisms. Unlike asexual reproduction, sexual reproduction results in individual genotypes of the offspring, which makes it harder for the parasite to adapt, forcing it to change, and vice versa, putting evolutionary pressure on the host to resist the parasite. Another theory, the handicap hypothesis, uses game theory to explain why males have traits that are unnecessary for survival. A peacock’s ornate tail and a stag’s antlers don’t help a male survive, but females see the handicap as evidence of survivability and health, so they choose those males, and evolution favors the handicap. Despite this explanation, the theory is limited by the existence of creatures with more than one sex, the fact that reproduction is not the only purpose of mating, and the difficulty of explaining homosexuality.
Another major mechanism of evolution is gene drift, which refers to the changing frequency of expression of alleles over generations. In general, in the case of sexual reproduction, a random combination of parental genes is passed on to the offspring, resulting in different traits even among children of the same parents. Without the influence of the environment, this would tend to be like the accumulation of sampling error in statistics. However, if certain traits are selected for by the environment, the frequency of traits that are favorable for survival will gradually increase, and the frequency of unfavorable traits will gradually decrease. If this process is repeated over generations, some genetic traits will survive and become fixed, while others will disappear. In other words, if individuals with the same genes live in different environments, they will be genetically separated and gradually fixate on traits that suit their environment, and eventually have opposite genetic traits.
It is known that the smaller the population, the faster the genetic drift. This means that if a small population is isolated in a particular environment, it can become fixed to a particular genetic trait very quickly. This situation is called a “genetic bottleneck” and can reduce diversity among individuals, threatening the maintenance of the species. The theory of neutral evolution, which considers gene immobility as a major factor in evolution, stems from the idea that most mutations in the genome have no direct effect on the individual. In the case of human DNA, more than 90% of the sequences are not involved in life activity and are just sitting there, so even when they do mutate, they have mostly neutral effects. The difference between the two theories is that, unlike natural selection, which explains that certain variants are selected for, evolution occurs when a neutral variant creates another allele, and that allele becomes fixed through gene drift. Evolutionists consider both gene drift and natural selection to be the primary factors in evolution.
Evolutionary theory has evolved over time and has found a lot of evidence, but there are inevitably gaps in the evolutionary tree. These undiscovered intermediate generations are called “missing links” because not all fossils can be preserved. You can think of this situation as being like a jigsaw puzzle. Just as you can’t find all the pieces of a jigsaw puzzle because they’re missing, but you can still infer the picture of the puzzle by fitting some of the pieces together, so too can the phenomenon of evolution be proven because there is enough evidence to support it despite the existence of missing links. Early evolutionists argued for gradualism, the theory that evolution occurs by the gradual accumulation of certain genetic traits over time. The idea is that most organisms have changes within the same lineage, and that these changes accumulate over time to differentiate into different species. As a result, the relatively slow and steady pace of evolution had to be explained by the existence of missing links, which was criticized.
However, the theory of intermittent equilibrium, which emerged in the 1970s, argues that evolution occurs mostly in short bursts of synchronized, rapid change, with no significant changes in the remaining long periods. According to this theory, the reason why missing links have not been found is likely because they don’t actually exist. Examples of interrupted equilibrium theories are organisms like silurians and ginkgo trees that don’t change much in traits over hundreds of millions of years, or strata where new kinds of fossils are found in rapid succession. This theory is distinct from gradualism in that it suggests that evolution may not occur over long periods of time, and instead may be much more active at certain times. However, there is no clear distinction between the time periods of evolution discussed in punctuated equilibrium and gradualism, and this is an area that needs further research. Richard Dawkins, a modern evolutionary theorist, believes that these theories can coexist rather than oppose each other, explaining that changes at the gene level follow gradualism, but phenotypes are discontinuous.
In modern times, evolutionary research has become more active as human genes have been better studied and biological analysis techniques have improved. Molecular biologists have discovered a phenomenon called horizontal gene transfer, which means that genes are passed directly from individual to individual without reproduction. This phenomenon suggests that genes can mix not only within the same species, but also between different species. It’s easy to demonstrate this phenomenon among microbes, and there’s evidence that it happens in most plants and animals. The chloroplasts of plant cells and the mitochondria of animal cells are prime examples. Unlike other organelles, they have separate DNA structures and double membrane structures, making it difficult to explain their origins. However, it is now believed that horizontal gene transfer led to an intracellular symbiosis that allowed both organelles to exist in the same cell. This discovery further expands the possibilities of how evolution could have occurred.
Epigenetics is another theory that proposes a new mechanism for evolution. When the theory of evolution first appeared, Lamarck argued for the theory of recombination. The theory states that acquired traits are inherited, which scientists in the past have refuted through experiments. Epigenetics, however, embraces some of the ideas of epistasis and argues that the environment affects gene expression. It says that the environment can modify the histone proteins that wrap around the DNA double helix, or change the methylation level of cytosine in DNA bases (the building blocks of nucleotides, the building blocks of DNA), thereby regulating the expression of genes. These changes in gene expression are known to be passed on to the next generation, and in the case of C. elegans, it has been confirmed that the vegetative record, a trait acquired by ancestors, is passed on to descendants. In higher organisms, this theory has not yet been clearly demonstrated, but further research may provide another mechanism for evolution: partial inheritance of acquired traits.
The concepts of evolutionary theory have been applied and studied in many fields, not just life sciences. Genetic algorithms, which emerged in the 1970s, were applied to solving “optimization problems” that attempt to answer all cases by introducing natural evolutionary processes into computation. Genetic algorithms think of genes as mathematical solutions, and analyze data by replacing processes such as selection, mutation, and crossover with computations. This technique has influenced the development of computer programming, and it has also led to the theory of evolution being taken out of the context of biology. In his book The Selfish Gene, Richard Dawkins argued that culture evolves like biology and proposed the meme as the basic unit of cultural evolution. Although the abstract concept of memes has been criticized, the public has embraced the novelty of introducing evolutionary theory into humanities research, and recent studies have shown the possibility that popular music can evolve through “selection” by the public. A team of researchers developed a random sound-modifying software called DarwinTunes and observed how noise gradually evolved into popular music through the evolutionary mechanism of “popular choice. The idea is that the choices of countless people can give direction to sound changes, eventually culminating in music. In addition, many researchers are conducting new studies using the concepts of evolutionary theory and reaching conclusions that overturn conventional wisdom.
Just as living things have evolved, the theory of evolution itself has evolved over time. Evolutionary theory is a combination of philosophical ideas and scientific evidence, and the concepts used to explain evolution have been applied to many different fields. So even if you don’t want to become a biologist, it’s worth studying evolutionary theory because it can be applied to your field.