Did You Know?
Darwin's Theory of Evolution is said to be in crisis due to the tremendous advances that have been made in biochemistry, genetics, and molecular biology over the past fifty years.
According to biology, the term 'evolution' has been defined as 'the change in the inherited traits of a population from one generation to the next'. The idea is that these genetic traits are passed on to the offspring during the process of reproduction. New traits enter the genetic pool when either a population migrates from one habitat (area) to another and adapts, or a species reproduces with another species. During this process, the 'final outcome' species that manage to adapt by either means tend to survive, whereas the unfit species become extinct. This process is called Natural Selection.
The Theory of Evolution based on the process of Natural Selection was first propounded by Charles Darwin in his book 'On the Origin of Species' published in 1859. In the same book, Darwin also maintained that all the species have descended from a common genetic pool. This theory has formed the basis of modern biological thought which explains the diversity of life on Earth.
The Varied Theories
There were 5 important theories that were put forth by Darwin, including Natural Selection. These have been explained below.
This refers to the process of varied species coming and going through time, and while they exist, they change.
This theory states that organisms have descended from one, or several common ancestors and have undergone diversification from this original stock.
The diversification process involves the populations of one species undergoing diversification until they are no longer one species, but become 2 separate species altogether. This process, it is said, has occurred billions of time before.
The evolutionary changes that take place, happen as incremental small changes within populations. It is not possible for a new species to be created suddenly.
Evolutionary change is brought about through variation between individuals. Some variants provide the individual with extra survival probability.
Darwin also went on to clarify that all these processes did not occur in isolation, that they were in fact a part of one grand idea, and that they all occur together.
The Workings of Natural Selection
Darwin observed that organisms produced more offspring than required to replace themselves such that population sizes would increase rapidly. This can be observed in the sheer number of eggs laid by spiders or frogspawn each year. This concept was termed as super fecundity.
In adding to this observation, Darwin also concluded that the population number tend to remain the same, they do not, for example, double in a year than what they were a year before. This concept was termed as steady population.
Darwin further stated that this disparity was brought about because of the limited resources that were present in terms of water, food, shelter, and places to sleep and mate. Which is what led to the conclusion that individuals competed amongst each other for scarce resources.
Darwin studied H.M.S. Beagles and pigeons extensively and came to the conclusion that individuals are unique and that individuals vary in almost every aspect.
He further studied that the individual differences that are found in species are heritable, which means that they are passed from parent to offspring. To reach this conclusion, he had taken to breeding pigeons to understand variability further. To do this, he performed many crosses between different breeds of pigeons to observe whether their offspring inherited the same variations. Not only pigeons, but also varied plants were studied to reach this conclusion.
Based on all these observations, Darwin drew two main conclusions which neatly sum up what the evolution theory is all about. Darwin realized that if all individuals must compete amongst each other and they are all unique in one way or another, then some individuals will possess certain variations which will give them a survival boost. This boost will then allow them to have better opportunities to reproduce and leave a greater number of offspring. Additionally, these offspring will then inherit the unique variations which made their parents successful and therefore, they too will have an advantage at survival. This differential survival of species with the successful variations, will, over time, spread through the population―leading to a change in the population and thus leading to evolution with time.
Darwin's theory and the successive theories that were drawn on the basis of the concept of Natural Selection have been subjected to several controversies. Chief among the people against the theory are the Creationists, who have a theological or religious basis for their arguments. They believe that a supernatural entity like God had a hand in creating man on Earth. Darwin's theory therefore stands against their long held beliefs and systems of religious thought.
When Darwin first came out with his theory in 1859, he faced a lot of opposition from not just the religious community, but also from the scientific community. However, the experiments that were conducted by other scientists in the field have revealed Darwin's theories to be true. However, the religious debate still continues.