Why We All Evolve: The Process of Natural Selection

In the early 1800s, Charles Darwin boarded the HMS Beagle and headed for the Galapagos Islands, completely unaware that he was on his way to discover one of the most important mechanisms of evolution. Over his five-year expedition, Darwin observed that each island contains different species of birds that are remarkably similar but have different variations among the population. From his observations of the organisms inhabiting the Galapagos Islands, Charles Darwin derived one of the most fundamental process of evolution known as Natural Selection, a process by which "organisms better adapted to their environment tend to survive and produce more offspring." The process of natural selection takes into effect as a species produces more offspring than can survive. Within this population, slight random genetic variations exists between different individuals that either facilitate or impede their ability to survive in a certain type of environment. Because parent organisms reproduce and give rise to an augmented amount of offsprings, there is a problem of supply and demand. The resources available, such as food, water and territory, becomes scarse and those individuals that have inherited an adaptable trait are the ones that will survive to reproduce and pass on that advantageous trait to the next generation, otherwise also known as "survival of the fittest". Overtime, more of the population has inherited this beneficial trait and has evolved to survive under certain environmental conditions, eventually leading to evolution. 

This fundamental process of natural selection can be be witness by analyzing the genetic variations found within the population of Grove snails (Cepaea nemoralis). 

Population of Grove snails that contains genetic variations in the form of shell color and banded patterns  

Random genetic variations in Grove snail populations exist in the form of shell color and the patterns adorning their shells. The effect of these random variations on an individual in the population demonstrate that genetic comes hand-in-hand with the process of natural selection. According to the article "Evolution at a Snail's Pace" by Smit Patel, various genes account for these visible genetic traits that effect organisms' chances of survival in a certain type of environment . Genes are units of hereditary that determine the visible and concealed characteristics of an individual which can be passed on to the offspring of the next generation. In the case of Grove snails, three different alleles that are controlled by a single gene (C), determines the shell color of a snail. The different alleles for brown (CB), pink (CP) and yellow (CY) shell colors are combined and mix-matched together through sexual reproduction. On the other hand, the snails' banded pattern is determined by a single gene with two alleles: B for non-banded and b for banded. These different alleles that control the snails' genetic traits give rise to random variation that becomes the driving force for natural selection. 

Grove snails with different colored shells respond differently to varying thermal properties. It has been proven that brown and pink snails more readily absorb ultra violet rays than those with yellow shells, which means that they are more adaptable to areas with cooler climates ie. a place with minimum amount of sunlight and heat. On the other hand, yellow Grove snails have been shown to be less incline in absorbing heat and so are more favorable in warmer climates. Over the past several years through the investigation of the Grove snail populations in various European regions, scientists have found that a correlation exists between geographical association of shell colors and climate. The results have demonstrated that there is an increase in population of yellow Grove snails in Southern Europe where the climate tends to be warmer than Northern regions. This relationship between the abundance of yellow snails and geographical locations with temperate climates has been induced by the process of natural selection. Because brown and pink snails are less likely to survive in warmer climates, their darker-shelled trait works against their advantage in Southern regions of Europe. Therefore, this minimal population size of darker snails in specific geographical locations is due to their inability to adapt to warmer climates and have instead evolved to survive in colder climates, where their hereditary trait allows them to survive on the the minimal amount of heat available.

Climate Map of European Regions. Yellow Snails are more likely to be found in Southern European regions where it is shown to be warmer. 

The case of natural selection presented above is an example of how abiotic factors such as climate can affect the way in which organisms evolve. However, abiotic factors are not the only element that influences the way in which organisms evolve. Another illustration of when natural selection comes into effect is the way in which male peacocks have evolved to have stunning, colorful tails. Over thousands of year, female peacocks have shown a preference for males with brighter and more attractive tails. This process, also known as sexual selection, is another element of natural selection derived by Charles Darwin. According to experts, male peacocks that had alluring tails were more ideal for sexual reproduction because they had the ability to signal females. Eventually, those that had brighter or "fitter" tails, which were attained through variations in genetic traits, are the ones to reproduce and pass on this hereditary trait to the next generation and become the dominant population of peacocks. Nowadays, male peacocks with unadorned tail patterns are rarely ever spotted because they lacked the advantageous trait that would've allowed them to mate and reproduce. 

Beautiful Peacock, expanding its tail to attract a mate. 

Sources: 

• http://www.merriam-webster.com/dictionary/natural%20selection
• http://www.news-medical.net/health/Genes-What-are-Genes.aspx
• http://www.thegreatdebate.org.uk/sexualselection.html