Mechanism of Evolution

Introduction

• Darwin implied that natural selection was a mechanism of evolution because those species that fit better in an environment will procreate more

• The mechanism of evolution tries to answer how variation and speciation amongst living beings occur

• While Gregor Mendel, a mathematician, and biologist, believed that inheritable factors influenced the phenotype, Darwin ignored these findings

• Gregor Mendel is known as the father of genetics and had propounded the following 

Laws of Inheritance

• Law of independent assortment- Mendel’s law of independent assortment refers to separating different genes from each other when the reproductive cells are developing. It also refers to the assortment of alleles of different genes into gametes. It is important to note that the allele received by one gamete does not influence the allele received by another gamete

• Law of segregation- Mendel’s law of segregation states that a diploid individual with an allele pair for all traits will pass the allele to its offspring randomly. It can also be stated that according to the law of segregation, a diploid organism with separate copies of its traits so that each gamete will receive the dominant trait

• Law of dominance- Law of dominance or the first law of inheritance states that during a monohybrid cross between heterozygous pairs, one pair of characteristics will dominate over the other. Mendel noticed that in the F1 generation, only one parental characteristic was expressed, and in the F2 generation, both parental characteristics were expressed. Therefore, the parental trait that was expressed in the F1 generation is dominant, whereas the other trait is recessive

• Other than Gregor Mendel, Hugo de Vries’ work on the evening primrose developed the idea of mutation. Hugo de Vries was a Dutch botanist whose mutation theory states that living organisms can develop changes to their genes. These changes can significantly alter the organism itself

• De Vries believed that evolution was caused by mutation and not minor inheritable variations, as Darwin had believed. And while variations in genes are minor and directional, mutations occur randomly and are directionless

• According to de Vries, speciation was caused by mutation. And this concept was developed as an alternative to Darwinism and would later be referred to as saltation. Saltation refers to the mutational change that is sudden and large, from one generation to another

5 Mechanisms of Evolution 

While there is some confusion regarding the number of the mechanism of evolution, some people believe that there are 4 mechanisms of evolution while others believe that is 5. In this article, however, we will discuss 5 mechanisms of evolution: mutation, gene flow, genetic drift, natural selection, and non-random mating. 

• Mutation 

Mutation refers to changes in the sequence of DNA. Mutations result from errors of DNA copying during cell division, infections by viruses, and exposure to ionizing radiation and chemicals called mutagens. Mutations that occur in the sperm and eggs and can be passed down to offspring are germline mutations. At the same time, somatic mutations that occur in the body’s cells cannot be passed down. 

Mutations that are caused due to environmental factors such as exposure to radiation are not part of evolution. Those mutations inherited from a parent and present in all of the body’s cells are mutations that lead to evolution. 

• Gene Flow 

Gene flow refers to the migration or transfer of genetic material from one population to another. Gene flow can occur between two populations of the same species, and the transfer is facilitated by reproduction. Gene flows from parent to offspring. Gene flow is an agent of evolution as it introduces new alleles or existing alleles in different proportions in the population. 

Gene flow can lead to evolution because of the migration and mating between two populations under different selective pressures and allele frequencies. 

• Genetic Drift 

Genetic drift refers to the random change in allele frequencies of a population. It is a matter of chance effect that is more notable within smaller populations. Genetic drift is a random sampling error that can occur in any population but significantly affects smaller populations. Genetic drift is very common amongst those species that undergo regular cycles of recolonization and extinction. It is also very common amongst small populations isolated from the significant population and established in a geographically isolated region. 

Bottleneck effect- The bottleneck effect is a type of genetic drift that occurs in populations that have decreased due to environmental factors like natural disasters. Major natural disasters like earthquakes, floods, and pandemics can lead to the depletion of genes. The genetic makeup of the surviving population becomes drastically different from the original population due to a reduction in the genetic diversity of the original gene pool. 

Founder effect- The founder effect is a type of genetic drift that occurs within a small population of individuals isolated from the larger population. Genetic drift occurs in these small populations due to the loss of genetic diversity. Due to their isolation from the majority population, these communities lose allele frequencies and can develop genetic traits that are more prevalent than others. A great example of such a community is the Amish community, amongst whom there are more cases of Ellis-van Creveld syndrome than the entire world. 

• Natural Selection 

Natural selection is an evolutionary mechanism. As per the principle of natural selection, the frequency of alleles that make an organism less fit to survive and reproduce in an environment will drop from one generation to the next. 

• Stabilising Selection- Stabilising selection is a natural selection where the intermediate trait is selected against two extremes of traits. The population will undergo stabilising selection when an intermediate or average phenotype is selected rather than an extreme variation. Stabilising selection is common amongst those populations where the genetic diversity has decreased as the population stabilizes on a particular trait. 

• Directional Selection- Directional selection is natural selection that occurs when selective pressures favour a single extreme phenotype. The directional selection causes the allele frequencies to shift in one direction. 

• Disruptive Selection- Unlike stabilizing selection where the intermediate trait is chosen, the selective pressures work solely in favour of the two extremes in the disruptive selection. Disruptive selection is a type of natural selection that doesn’t occur commonly. Disruptive selection drives speciation when environmental changes favour extreme phenotypes over intermediate ones. 

• Non-random mating

Non-random mating is a contentious mention as it’s debatable whether it causes evolution. Non-random mating is between organisms with the same genotype or different genotypes. Non-random mating cannot change the allele frequencies; however, it can change the genotype frequency. 

Conclusion 

With this, we conclude our article on the mechanism of evolution. We hope that you found our article illuminating. With this, we conclude our article on the mechanism of evolution. We hope that you found our article illuminating. The concept of the mechanism of evolution tries to determine the reason behind speciation and variation amongst living beings. While Charles Darwin believed that natural selection was the only mechanism of evolution, on the other hand, Gregor Mendel, considered the father of genetics, propounded three laws of inheritance- the law of independent assortment, the law of segregation, and the law of dominance.