Darwin’s Theory of Evolution

Evolution is the law of life and every organism is the result of their ancestral evolution. Evolution is the gradual change of the inherited traits of a biological population over subsequent generations. Traits are the phenotypical expression controlled by their inner genetic composition. It is said that all the organisms have come from a single cell and there has been a lot of research conducted by scientists in this regard. We see that some of the organisms remained unicellular( amoeba)  and some have been restructured into gigantic and complex bodies( such as whales). This is probably becasue the way they have undergone through the influence of evolution. Among all the species, human beings are the highly evolved species. Why is it so?  It is becasue of the series of evolutionary reforms that happened through centuries in them. Charles Darwin is well known as the father of evolution. He is the author of a famous book ‘Origin of Species’ which is well known as Darwin`s theories. According to his book, he has drawn the conclusions as shown below.


1. Organisms have an unlimited capacity to reproduce:

Organisms need to survive and sustain, so they have to replicate at a rapid pace and they have the capacity to do so. As a law of nature, each organism has to struggle for their day to day survival. The chances of survival is good if the organisms are able to prove their ability against all odds. For example; if a fish laid 100 eggs, most of its eggs are eaten by their prey,  resulting in the survival of a very few . In this case, the fish might have struggled to help in the survival of the existing eggs. In the journey of life, each organism has its own capacity to struggle and exist, in this case, fish has the unique ability to produce so many eggs so that at least a few eggs can survive.  

2. Theory of Natural Selection:

Every species possess different traits becasue nature has assigned them in such a way that different traits help in the survival of different organisms in a different way. In simple terms, each organism has a particular trait that assist in finding it`s food and shelter. In such a process, only those individuals possessing the most advanced traits can only be able to reproduce and survive for the future generation. This is the essence of natural selection.

3. Survival of the Fittest:

According to this law, better the fitness of an individual, greater the survival rate. This is the reason different organisms are placed at different levels of their pyramid. Such a process has led to the possibility that many species have gone into extinction ( weaker ones) but the stronger ones survived. This is the reason that mighty animals stay at the top of the food chain and the smaller ones stay at the bottom.


Concept of Speciation:

Speciation is the process of origin of a new species. A group of organisms with similar features are known as species and these members are able to breed among themselves. The main trigger for the formation of new species is when two groups of the same species are prevented from interbreeding for several generations due to geographical segregation or because of some genetic changes. The evolution of new species, because of geographical segregation is called genetic drift. On the other hand, microevolution is a small scale version of evolution for eg, change in the body colour of beetles over a period.


Concept of evolution and the classification of organisms

Evolutionary classification is also known as phylogenetic classification. The modern system of classification is closely linked with the evolutionary relationship of species. In an evolutionary classification, the kingdom is the highest taxa, whereas the species is the lowest. The members of a species share much of their characters in common when compared to the members of a kingdom. For example; all human beings come under the species Homo sapiens and they can interbreed irrespective of whether they are black or white, Asians or  Americans and so on. Similarly, all human beings come under the class Mammalian encompassing different animals such as monkeys, chimps, elephants, and cows, etc where very few characters of all mammalians resemble but they cant interbreed easily. Some of the similar traits in these mamas can be the hair on the body and the mammary glands in females. Similarly, every animal cell lacks cell wall irrespective of whether the organism is a monkey or donkey or human being. This means in some way we, all animals, share something in common. The degree of similarity or dissimilarity shows that all animals have evolved from a common ancestor.


Concept of homologous and analogous organs

Homologous organs

Homology (means same) is the similarity that is inherited by two organisms from their common ancestor. Organs such as wings of a bat, hands of human beings, bird wings, flippers of seals, forelimb of a horse, etc, have a common universal fundamental anatomy but different organisms use this anatomy for different purposes. Horses use their forelimbs for running, human beings use forelimbs (upper limb) for holding something or working but whales use their flippers for swimming. 


Homologous organs-image from brainly.com


Analogous organs

Analogy is about how two different organisms perform a similar function as a result of the evolution process despite that they do not share the common ancestry. For example, how wings of insects, bats, and birds have evolved autonomously from their family separately after diverging from an ancestor without wings. The wings of insects start off from the inner or outer surface of the insect’s body and the whereas the feathers of birds originate from their forelimbs. Similarly, the wings of bats grow out from both the forelimb and the membranous skin of their abdomen. 


Fossils and evolution 

Fossils are evidence of evolution. Fossils are the preserved fragments (remains) of many organisms from their past. It can be from hundreds to thousands of years but, to classify a fragment into a fossil, it must be 10,000 years old. Fossils tell us the story of many extinct animals, for example, dinosaurs which we frequently see in movies and other media.