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Relationship Between Natural Selection and Evolution


Can selection occur without natural selection?

Background

Genetic Drift is a change in allele frequency in a population due to random selection of genes. Mutations in the DNA can have no effect on the fitness of an organism. This means that even if evolution has occurred natural selection would not. These genetic changes can increase or decrease among the population. When an allele does not change the frequency in a population then genetic drift is acting on the allele. Allele frequencies tend to stay relatively stable in large populations because the gene does not affect fitness. However, in small populations fluctuation can occur leading to evolution - some alleles will become fixed and while others will disappear. 

Genetic Drift in COVID-19 

The genome of coronavirus is prone to mutations that can lead to genetic drift. It is crucial for vaccine developers to consider the sub-strains mutations. By using epitope information in spike protein (S), nucleocapsid protein (N), and membrane protein (M) in SARS-CoV2, in Koyama et. al., researchers found several variants that might cause drifts. One of the variants that were analyzed was the 23403A>G variant (p.D614G), which has a frequency in the spike protein B-cell epitope in European countries. 

Table 1: Variants in epitopes in spike protein (S), nucleocapsid protein (N), and membrane protein (M) in SARS-CoV2. [2]

Table 2: 23403A>G variant (p.D614G) statistics in spike protein observation by country. [2]

Among the variants found in the B-cell epitopes, 23403A>G variant (p.D614G) stands out, it is the one with spike protein between residue 601 and 640, it was found in 175 samples of 615. The variant involves a change in large acidic residue D which is aspartic acid into small hydrophobic residue G which is glycine. The differences among both of these amino acids include large size and hydrophobicity in the epitope, this mutation comprises the binding affinity to antibodies trained by vaccines wild-type sike protein. In Europe, most of the infected patients have this variant, so it is critical for vaccine design, and convalescent plasma antibody treatment may result in further considerations to accommodate the drift in this variant. 

Can natural selection occur without evolution?

If the differences among individuals are not genetically based then natural selection can occur without lead to evolution. Offspring do not always resemble their parents due to phenotypic variations - not due to different genes but different environmental conditions. So, if variation in a population is not genetically based, then selection will not lead to evolution. 

Work Cited: 
[1] https://biologydictionary.net/genetic-drift/ 
[2] Koyama, Takahiko; Weeraratne, Dilhan; Snowdon, Jane L.; Parida, Laxmi. 2020. "Emergence of Drift Variants That May Affect COVID-19 Vaccine Development and Antibody Treatment" Pathogens 9, no. 5: 324. https://doi.org/10.3390/pathogens9050324
[3] https://sandwalk.blogspot.com/2013/11/natural-selection-may-not-lead-to.html#:~:text=Natural%20selection%20can%20occur%20without,individuals%20are%20not%20genetically%20based.&text=Nonetheless%2C%20much%20of%20the%20phenotypic,does%20lead%20to%20evolutionary%20change 


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