There are many views on how to define evolution. These often-conflicting definitions of evolution only add to the confusion that many people have about how to interpret the subject.
Evolution is defined in the textbook “Biological Science” as the change in allele frequency over time. An allele is a part of a gene that accounts for variation within a population of organisms.
For example, if you look at the squirrels running around outside, you will see different lengths of tails within the squirrel population.The variance in tail lengths is because each individual squirrel has a unique DNA sequence that is derived from its parents’ own unique DNA sequences.
In each squirrel there is a gene within their genome that instructs the cells in the squirrel’s tail to multiply and form a unique squirrel tail at a specific length. Allele frequency is the rate of occurrence of a specific allele within a population. There would be a shift in allele frequency if over the course of time the number of longer tailed squirrels decreased compared to shorter tailed squirrels.
This basic example is a good representation of evolution occurring in its most basic form. Many people will think that this definition is too simplistic and will try to redefine evolution with a lot of clarifying statements, however, evolution is a very straightforward and observable phenomenon. Many people have become confused about evolution since other concepts, such as natural selection, are merged into society’s understanding of evolution.
Natural selection is a process though which alleles become more or less common within a population depending on the reproductive success of organisms within their environment. For example, lets assume that the squirrels with the longer tails are considered to be more attractive and desirable as mates. However, the longer tail is heavier to run with than a shorter tail and as a result the longer tailed squirrels can’t outrun their predators nearly as well as the shorter tailed squirrels. Since predators can catch the longer tailed squirrels, the long tailed squirrels tend to have a shorter life span than the shorter tailed squirrels.
However, since the longer tailed squirrels are considered more attractive as mates, then the first squirrels to mate each year are the longer tailed squirrels, so their genes are passed on to their offspring. The short tailed squirrels tend to live longer lives, so they have a greater span of time to find a mate and reproduce. This is how there are both long and short tailed squirrels running around. There are advantages and disadvantages for both tail lengths, so the reproductive advantage is highly situational.
Natural selection is just one mechanism that furthers evolution. Natural selection is colloquially defined as the survival of the fittest. In some ways, this definition is accurate, but the term ‘fittest’ needs to remain relative to the situation. The biological definition of fitness is the ability to survive and reproduce. In terms of traditional evolutionary theory, if the alleles of a given gene affect the ‘fitness’ of an organism, then the frequencies of these alleles will change (thus evolution is promoted).
Evolutionary theory is most highly disputed by its critics with regards to the scientific pursuit of a universal common ancestor. Many scientists believe that all organisms stem from a common ancestor from billions of years ago. The oldest estimate at this point is that the most recent universal common ancestor lived about 3.9 billion years ago. Biologists and geologists are continuing to unearth new remains that add to the study of evolutionary theory.
One of the best established cases of fossilized evidence of a creature predating Homo sapiens is the 1972 discovery of ‘Lucy,’ the female Australopithecus afarensis. Scientists estimate that the bipedal ape is 3.2 million years old and is an ancestor of Homo sapiens. There are skeptics within the scientific community that question if ‘Lucy’ is a common ancestor to Homo sapiens due to her short stature and ape-like bone structure (such as her curved toes and a hip bone that only would support bipedal movement for a short duration).
Still, many seek to uncover more about humanity’s ancestral past and try their best to interpret the physical evidence as objectively as possible. Events such as the Scopes Monkey Trial and the more recent Nye-Ham debate have created a highly politicized and emotional approach to the study of evolution. There is far more work and research that needs to be done to discover the past history of our world, but through observation of the behavior, appearance and genomes of living organisms, scientists can use these living models to learn how the universe functions and has continued to have functioned throughout the millennia.