Difference between Genetic Drift and Natural Selection
In this post, we will know about the key differences between Genetic Drift and Natural Selection. After reading this post, you can perfectly differentiate the two of these very clearly.
Make sure to read this complete post to understand the topic very clearly and precisely.
Genetic drift, and natural selection, may sound similar or even confusing to some as these are two of the important and related factors in evolution that deal with the change in alleles and adaptation of the species causing microevolution and macroevolution.
Both natural selection and genetic drift are the mechanisms of evolution. Both show the change in the heritable traits of a population over generations.
Natural selection is a mechanism of evolution that shows adaptations of the species that are affected due to the pressure implied on them by the natural environment.
Whereas, Genetic drift is a mechanism of evolution in which allele frequencies of a population change over generations due to chance or randomness but adaptations don’t occur.
Natural selection states that the organisms that are more adapted to their environment are more likely to survive and pass on the genes that aided their survival. This process causes divergent evolution and specialization.
Genetic drift states that the genetic makeup of the population changes over time which is an entirely random process. So, although genetic drift is a mechanism of evolution, it doesn’t directly work to produce adaptations.
Let’s know more about them with precise detail and comparison.
Comparison Chart: Genetic Drift Vs. Natural Selection
| NO. | GENETIC DRIFT | NATURAL SELECTION |
|---|---|---|
| 1. | It is a mechanism of evolution that leads to microevolution. | It is a key mechanism of evolution that leads to macroevolution. |
| 2. | Genetic drift causes changes in allele frequencies over time at a small-scale within a short-time period. | Natural selection causes changes in allele frequencies over time at a large-scale in a very long-time period. |
| 3. | It is mostly seen in small populations. | It is seen in large populations. |
| 4. | Genetic drift can result in the loss of rare alleles, and can decrease the size of the gene pool. | Natural selection can cause the creation of beneficial alleles, and the removal of harmful alleles and can both increase or decrease the size of the gene pool of many populations as a whole. |
| 5. | It occurs randomly or by chance due to sampling error in a population. | It occurs when the selective pressure of nature acts on an organism. |
| 6. | Genetic Drift needs other factors like gene flow, mutation, natural selection to cause adaptation in an organism. | The effects of Natural selection alone can cause adaptation in an organism. |
| 7. | Genetic Drift cannot cause speciation. | Natural selection can cause speciation over time. |
| 8. | The occurrence of genetic drift can be harmful or beneficial to the organism. | Natural selection brings only beneficial changes/adaptations in a living organism. |
| 9. | Genetic drift is random and based on luck. | Natural selection is influenced by changes in environmental conditions. |
| 10. | It occurs in the absence of positive or negative selection pressure on the organisms. | Natural selection is a broader term that occurs due to the successive repetition of many genetic drifts along with gene flow events, mutations happening over time. |
| 11. | There are two types of genetic drift: bottleneck effect, and founder effect. | There are three types of natural selection: directional selection, stabilizing selection, and disruptive selection. |
Definition of Genetic Drift
Genetic drift is a mechanism of evolution in which allele frequencies of a population change over generations due to chance.
It can result in the loss of some alleles (including beneficial ones) and the fixation, or rise to 100% frequency of other alleles.
Alleles are just the different versions of the same gene located on the same locus of a chromosome. And, allele frequency refers to how common an allele is in a population.
Genetic drift shows that evolution (more commonly microevolution) can take place by chance which may be due to natural selection or some other evolutionary mechanism.
Genetic drift is a mechanism of evolution that produces random changes in allele frequencies in a population over time rather than selection-driven.
Genetic drift is more finely seen in small populations within a short period of time over generations, although it can also happen in large populations but takes a long time as the population is large.
Genetic drift alone can’t produce any type of adaptation in an organism because it’s a random occurrence. But when natural selection, mutation, and gene flow also happens along with genetic drift than adaptation definitely occurs over time.
The occurrence of genetic drift can be harmful or beneficial to the organism. It depends on the change in allele frequencies.
If a beneficial allele becomes dominant in a population than it is good, and if a harmful (deadly) allele becomes dominant in a population than it may cause death overtime.
For example: In a mice population, the allele frequency of the dominant B allele (black fur) is 40% and the allele frequency of the recessive b allele (brown fur) is 60%. This shows that more brown fur mice are present in the population than the black fur ones. This is proof that the population of mice is evolving due to genetic drift.
Definition of Natural Selection
Natural selection in evolution is a cause or reason that supports the organisms to better adapt to their environment in order to better survive and produce more offspring that can withstand the environment.
Natural selection is a key mechanism of evolution that directly leads to adaptations because it is based on the evolutionary phenomenon of the survival of the fittest.
The survival of the fittest in natural selection states that nature selects only those individuals who are with favorable variations and are best adapted to the environment. The less fit and unfit organisms die and are eventually destroyed.
Evolution is related to natural selection as only a way that supports and causes evolution.
Evolution deserves better adaptations of the organisms to their environment, and natural selection is a gradual process of how the organisms adapt themselves to evolve to better withstand the environment and pass the adapted characters to their offsprings.
Unlike genetic drift, natural selection is not random but due to the selective pressure of the environment on the organism. It brings only positive or beneficial change/adaptation in the organism towards its environment.
Natural selection means that adaptions occur naturally without any artificial involvement. When the organism finds it very hard to live in its habitat it develops various ways phylogenetically and genetically to make its survival a lot easier.
Natural selection selects those genetic mutations that make the organism most suited to its environment and therefore more likely to survive and reproduce. Thus, supporting a better type of evolution.
In this way, it can better adapt to its habitat (environment) and these adapted characters get passed to next-generation and gradually over time leads to speciation (formation of new species).
For example: In a habitat, there were both red bugs and green bugs. The birds prefer the taste of the red bugs and so they ate it more often. So soon there were many green bugs and few red bugs. The green bugs reproduced and made more green bugs and eventually there were no more red bugs.
So, natural selection happened here causing the adaptation of the various red bugs to green bugs just in order for the bugs to survive from the birds and continue their generations. And, those red bugs that failed to adapt themselves to green bugs were killed by the birds.
Key Differences Between Genetic Drift and Natural Selection
1. Genetic Drift is a type of small-scale microevolution. Whereas, natural selection is a type of large-scale macroevolution.
2. Genetic drift doesn’t lead to speciation. But, natural selection leads to speciation.
3. Genetic drift leads to changes in allele frequencies that are random. Natural selection also causes changes in allele frequencies but it’s not random.
4. Genetic drift occurs in the absence of selective pressures. Whereas, natural selection occurs in the presence of selective pressures.
5. The occurrence of genetic drift can be harmful or beneficial. Whereas, the occurrence of natural selection is always beneficial in nature.
6. Genetic drift doesn’t lead to adaptations but variations in a population. Whereas, natural selection leads to both adaptations and high level of variations.
Conclusion
Both natural selection, and genetic drift along with gene flow, and mutation are the four mechanisms that cause evolution and leads to changes in allele frequencies over time.
When one or more of these forces are acting in a population, the population violates the Hardy-Weinberg assumptions, and evolution occurs.
Natural selection is the most important concept in evolution. It is in fact, the most important mechanism of allele-frequency change, and it is the only mechanism that generates adaptation of organisms to their environments.
Other small-scale mechanisms like genetic drift, gene flow, mutations, etc. also contribute to changing the allele frequencies over time as so are very important for evolution to occur.