The Earth is home to an innumerable amount of plant and animal species, with any estimate ranging from 2 to 50 million being as good a guess as any. 950,000 kinds exist within the insect class alone, while annual naturalistic publications are often able to showcase up to 10,000 newly discovered species. This incredible genetic diversity is preserved by unique natural phenomena known as isolation mechanisms to prevent accidental matchups between different species. But how did so many different types of plants and animals develop in the first place? What was the driving force behind our planet’s rich variety of living organisms?
The answer to that question in a general sense lies in the theory of evolution, first proposed by Charles Darwin in 1842 and later published in his On the Origin of Species in 1859. A brief outline of the theory suggests species change over time as a response to challenges presented by the natural environment. Evolution, however, is a very broad conception and thus our simple definition fails to account for the differences occurring between many closely related species. For instance, it does not explain why one parrot raised for years on end remains mute, while its slightly larger and brighter-colored cousin appears to have learned every single tune and children’s rhyme imaginable.
Proposing to answer this question as we go, let us introduce the term speciation. John Gittleman writing for Encyclopedia Britannica provides the following insight: “Speciation, the formation of new and distinct species in the course of evolution. Speciation involves the splitting of a single evolutionary lineage into two or more genetically independent one”. One way to understand speciation is taking it for a structural subdivision of evolutionary study, concerned with research into the appearance of new biological species. Species, in turn, are defined by author Philip McClean as “a group of populations through which genes can flow and whose offspring have a fitness equal to the parents”. Therefore, a species is distinguished by its ability to interbreed successfully only with individuals baring full genetic resemblance to it. In order for a new species to form under such exigent conditions, scientists agree the most important factor is geographic isolation of one group of individuals from the rest of the population. Only then can natural selection begin to play its role in shaping the process of evolution.
Theoretically, the amount of species potentially able to develop from a single parent type is limitless. Whenever a small flock is cut off from a large habitat shared by many other animals, it usually means that the conditions of this new environment differ greatly from what was customary for the group. Natural selection will commence to adapt each following generation to its surroundings, slowly erasing traits from the parent species which do not contribute to the descendant’s survival. The process is deemed complete when the resulting animal or plant no longer exhibits reproductive behavior in regards to the original species, even if the two were to be reunited in the field. In this case, adaptation leads to the appearance of a distinct new species. Speciation has taken place.
There are times, however, when adaptation does not go all the way. Some types of living organisms inhabit different geographical locations (and even climate zones), while keeping diversity to a minimum. These derivations are known as “races”, or subspecies, who retain their mating capability with individuals of the parent species. Biologist John Kimball describes one such occurrence: “The seven distinct subspecies or races of the yellowthroat Geothlypis trichas (a warbler) in the continental U.S. would soon merge into a single homogeneous population if they occupied the same territory and bred with one another”.
A factor identified as ecological opportunity may offer an explanation for how finches split into so many separate classes. What this means is that upon immigration from Central or South America, the finches’ ancestor was not threatened by any predators and came across few competitors. Food was abundant, however, its sources varied somewhat in different parts of the archipelago. Depending on the place an individual flock chose to settle, it had to adapt, but could do so in a relaxed environment, allowing most groups to survive and evolve unparallel to others.
Nature has created a combination of factors responsible for preventing hybridization between species and ensuring all types of organisms maintain their eccentricity. They have been mentioned in this paper’s introduction under the name of isolating mechanisms. These instruments forestall possible cases of fertilization and incubation by either precluding the possibility of copulation altogether or denying zygotes the opportunity to develop. Isolating mechanisms are divided into prezygotic and postzygotic accordingly. Even if a hybrid creature is born, in most cases it will remain sterile into adulthood (the mule being the most common example).
In some cases, isolation leads to animals or plants slowly changing their appearance, or evolving for no particular reason. Even when there is no need to adapt, genetic modifications take place, owing to the principle of dominant and recessive gene inheritance. Smaller populations may for obvious reasons eventually grow to be homozygous for dominant genes, while recessive traits may disappear among the group altogether. This form of passive evolution is called genetic drift.
In order to summarize the paper’s contents, one should derive the following information from the text: speciation is the process by which new biological species arise as result of evolution. It occurs mainly due to isolation of animal flocks, herds or other social groups, from a larger formation of individuals. Conditions necessitate the small group’s adaptation to its surroundings. Confinement may also trigger evolution for no reason due to genetic drift. Once a new species has formed, it will be unable to interbreed with the parent species upon reunion. Particularly relaxed conditions may increase the number of kinds of animals spawned from a single ancestor.
References
Gittleman, John. “Speciation”. Encyclopedia Britannica. Encyclopedia Britannica, n.d. 27 Aug.
2014.
Kimball, John. “Speciation”. Kimball's Biology Pages. Kimball's Biology Pages, n.d. No date.
McClean, Philip. “Speciation”. Population and Evolutionary Genetics. Population and
Evolutionary Genetics, n.d. 1997.
