Introduction

Natural Selection is one of the main concepts found within the theory of evolution. It was discovered by Charles Darwin and Alfred Russel Wallace.  Darwin is most often credited with popularizing the concept in his book “On the Origin of Species”.Natural selection can be defined as the process by which random evolutionary changes are “selected” for by nature in a consistent, orderly, non-random way. We will explore this concept in more detail now…

Learning

Theories of where we came from and where did the earth come from were based on religious doctrine up until the 1700’s & 1800’s.

Earliest theories:

• Plato 427-347 BC and student Aristotle – all organisms were created by God
• God created all organisms at the same time
• All organisms have been unchanged since then

Later, scientists based their theories on this “unchanged form” idea:

• Earth center of universe – man pinnacle of creation
• This worked until 1700’s when more evidence started to come up

The 1700’s and 1800’s were a time when people started to be on the move. Countries were taking over new territories, plus the industrial revolution, these factors contributed to exciting new evidence being discovered. Fuel was needed to move around and run the factories, therefore they had to dig, which resulted in the discovery of ‘rocks’ that were in different shapes, like the bones of animals. What were they? Educated people had ideas and guesses but universities at the time were solely run by religious organizations, because they had the finances to do so. In other words religion was the rule of thought at that time and you did not go against the church.

Fossils

As was mentioned, during this time people started to travel and dig into the earth, finding new objects we now call fossils. But what were these new objects and where did they come from? People initially believed they were just ordinary rocks that forces happened to make into lifelike forms. As more fossils were found though it became obvious they were remains or impressions.

Fossils are any part or trace of an organism that is preserved in rock or sediments is a fossil. When animals die, if these animals are covered up immediately say by soil, they have the possibility of being turned at least partially into rock. If dead animals are not covered up and are instead left exposed to the open air, then they become “lunch” for the surrounding animals.

Covered, carcasses are hidden from predators and the process of decomposing is slowed or stopped due to the lack of oxygen that bacteria and fungi need to decompose the object. Over time the bones become similar in makeup as rock but of course still in the shape of whatever the animal was.

Fossils of bones and entire skeletons are what people are most familiar with, but fossils can also be fossilized feces (coprolites), which are more numerous because animals are always eating, and the waste products are always coming out. They can also be skin impressions or footprints.

Preconception

By 1859, it was only a matter of time before someone “discovered” evolution. But why did it take so long? When there is a strong preconception about what a pattern means, or what it represents, it can stop you seeing it in any other way.

Charles Darwin was simply the first person to write down what everyone was thinking. He did not set out to do this, he just was curious and collected evidence from the natural world on his trip on the HMS Beagle from 1831-1836. Alfred Wallace also had evidence of evolution. Darwin knew this and published the evidence in his book, On the Origin of Species many years later in 1859. His book sold out the day after publication.

Darwin’s book contained two major points:

1. All things alive have descended from earlier species.
2. Species have been modified through generations to survive.

Based on these two things, he then proposed a mechanism called natural selection. In the process of natural selection, the particular organism that is being “modified” in a population is already IN the population. For example, antibiotic resistance in bacteria was always there, the mutant gene that makes some bacteria resistant was already present, just in a low frequency. The gene did not show up in response to the antibiotic. The mutant gene increased in frequency due to the antibiotic killing off the non-resistant bacteria. They died off and the bacteria that were (already) resistant are the only ones that survive so they then increase in frequency.

Principles of Natural Selection

1. Natural Selection does not cause genetic changes in individuals. Rather, natural selection may favor certain individuals possessing certain traits.
2. Natural Selection can affect the survival of certain individuals, but only populations are changed or shaped by Natural Selection. If an individual can survive, they can reproduce and pass on the genes to the next generation, starting a (usually rather slow) shift in the allele frequencies.
3. Natural selection does not have a direction. Individuals possessing certain traits may be better suited for survival in a particular environment while other traits may result in a disadvantage.

Summary

• In this section, we have learned the following: Natural Selection is one of the key driving forces of Evolution.
• Fossils were being “recognized” as evidence of organisms that lived in the past
• Darwin proposed two core ideas:
  • ‘Descent with Modification’
  • ‘Common Descent’
• He proposed that nature could also ‘select’ organisms; a process he termed ‘Natural Selection’ with three principles:
  1. Natural selection may favor individuals with certain genetic traits.
  2. If an individual can survive, they can reproduce and pass on their genes to the next generation.
  3. Natural selection does not proceed in a certain direction.
• Charles Darwin’s work provided the link between random genetic events (Descent with Modification) with the generation of new species on earth.

---

^Sources:

National park Service, image of fossils, Courtesy: Nation Park Service. May 22, 2021. Retrieved from: https://www.nps.gov/subjects/fossils/index.htm

Motion illusion in star arrangement.png. Image. May 23, 2021. Wikimedia Commons / CC-BY-SA-3.0

Understanding Evolution. (2021, March 6). Retrieved May 22, 2021, from https://bio.libretexts.org/@go/page/1916.