Mechanisms of Evolution

Prologue to evolution

The theory of evolution is one of the most fundamental models in modern science. Evolution itself is change in characteristics of populations over generations. That means some traits in groups of organisms living in determined conditions, develop gradually to survive. In the series "Theory of evolution" we will take a journey that led to life as we know it. Let's start with the basics. Since its forming the theory of evolution has changed in some aspects. However, the very fundamental, the key to understanding the concept, is the collection of mechanisms that direct the process.  They were formed by Charles Darwin as a result of his famous studies on Galapagos, and are accurate for the entire life on Earth. We ought to remember that those mechanisms not only led to life as we know it today, but are still ongoing, though the results will be observable in hundreds of years.



The evolution of life. Credit :https://cdn.images.express.co.uk/img/dynamic/151/590x/secondary/Evolve-life-403310.jpg

Mechanisms of evolution are outcomes of variation

Theory of evolution establish that organisms of one species are different from one another. It is easily observable all around us, just look at the people on the street! Phenotypic variation (one you can so easily observe) has its background in the genetic one. It can be identified by observation of quantitative or discrete traits. Quantitative traits are coded by many genes, so you cannot isolate variants (like height, skin colour, weight etc.). In contrast, discrete traits are coded by one or a few genes, so there is a limited number of combinations and we can easily isolate variants (like petal colour in certain flowers, marking in certain animals). Another important factor is variation between animals living in different conditions (it’s called variation between population). It is the result of phenotypic plasticity- ability of genes to adapt to condition by changes in phenotype.

Variation among one species.
Credit: https://james.westgard.com/.a/6a00d8354de03569e2019b0124fe80970d-pi

Natural selection

Natural selection is an outcome of variation in a very simple way. If we’ve established that there are differences between organisms among one species, then organisms with best traits are more likely to survive. Moreover, individuals with best variants of genes will easily find a partner and litter. Therefore, this hypothetical good trait will be passed among generations and spread forward and weak organisms without good variants of traits will die with less or no brood.

Let’s apply an example of evolutionary battle between giraffe and  acacia.  Millions of years ago giraffes weren’t exceptionally tall, though there were some differences in their heights (let’s call them great-giraffes). Great-giraffes ate leaves of acacia, but taller ones had access to leaves other couldn’t reach. As acacias started growing taller and taller, which was because taller plants weren’t so badly damaged by feeding animals, height became more important for survival. All in all tall individuals survived more often, litter more often, and therefore average height among Great-giraffes increased up to a point when they became giraffes we know today (of course there were many other processes involved and way larger changes, though that is a route of change in height).

Evolution of giraffe. Credit: https://static.bioscience.com.pk/media/k2/items/cache/7d2898c3630feea92ec1553d16389ff6_XL.jpg

Mutations

Another important of the mechanisms of evolution is a sharp change in genetic material called mutation. Not every mutation is hereditary. Ones that are passed to the next generation are called generative and they are the one evolution is interested in. Most of mutations are punctual and neutral, so they do not create any change in the organism. Some are adverse, which mean they can cause diseases or even be lethal. However, there are also mutations that create positive effects and, if they are generative, can change a species a lot. Some mutations pass to then next generation, some appear during an error in process or as a result of activity of mutagens. Moreover, the phenotype-first theory establishes that mutations can cause some traits to assimilate, if environment induced them before.

Mutation in genes.
Credit: https://cdn1.medicalnewstoday.com/content/images/articles/318/318492/dna-strands.jpg

Genetic drift and gene flow

Firstly, most genes have multiple variants (allele) that create a different visible effect. When the frequency of chosen allele changes, due to the fact that organisms pick each other randomly to neutral traits, we call it genetic drift. It leads to a fluctuation between content of different variants in the generation. Sometimes it leads to disappearance of some alleles, therefore reducing variation. Gene flow is simply transfer of genetic variation between populations. Every population has its own traits depending on the environment. When the populations mix, some of those traits move from one population to another. If, at some point, both population have the same allele frequencies, as a result they become one, bigger population.

Gene flow.
Credit: https://biologydictionary.net/wp-content/uploads/2018/09/Gene-flow.jpg

Conclusion

In conclusion, natural selection, mutation, genetic drift and gene flow are basic mechanisms of evolution. They have been directing the process since the beginning of life and are the key to understanding the entire theory. We should remember, that they impact each other and happen at the same time, creating unique outcomes we see.

Author’s message

The Theory of Evolution is the third series on The Secrets of the Universe. The first two series, Quantum Week and Basics of Astrophysics received excellent response. I hope in this article you learned about basics of evolution and that it encouraged you to study the subject. In the next articles we will discuss basics of evolution theory and its importance for everyone. Mechanisms of evolution has led us through millions of years and I want you to take this beautiful journey with me. If you want to study more of the subject, check out the external links, feel free to contact me and share the article if you enjoyed it.

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