Darwin’s Theory of Evolution


Evolution is the law of life and wewouldn`t have been where we are today if there is no evolution .All our ancestors undergone a series of evolution and going forward, our generations are further evolved to give birth to the most advanced humnas. Evolution is not an overnight magic, instead, it is a gradual advancement of the inherited traits of a biological population over succeeding generations.


Nature of human evolution

Evolution encompasses a positive changes in the genotypical and phenotypical expression of the organisms. A genotype is the genetic composition of an individual and it is key factor that controls the physical expression of species ; phenotype.  All the organisms have evolved from a single cell but none of us are unclear about from where does the first cell originated . Furthermore , there is a lot of skepticism about why are some organisms  unicellular while many are multicellular lifeforms? Few scientists argue that every organism is different probably because of the factors surrounding them, which is what differentiates the organisms into unicellular, multicellualr, large, tiny, minute, tall, short etc. Nevertheless, human beings are the highly evolved species among all others because of the series of evolutionary progressions happened through millions of years. Charles Darwin, author of a famous book -"Origin of Species" . He is well known as the father of evolution and he who explained in detail about evolution with the help of  theories called Darwin`s theories. He postulated a few laws and they are most popularly called  as theories of evolution and this article explains about Darwin's theory of evolution.


Darwnin`s theory of evolution

1. Organisms have an unlimited capacity to reproduce

Darwin believes that the reproduction is the basis of continuation of survival of organisms through generations. However, each organism differ in terms of the pace, numbers and their capacity to reproduce; for instance, a fish can lay thousands of eggs whereas human beings are born as single or twins and very rarely triplets or more. Another important factor we can note here is that the survival rate of human progeny as very high whiloe compaed to the fish because hardly few eggs turn into organisms . Darwin has strongly argued that the chances of survival is high if the number of potential reproducing organisms are less. Therefore, 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 to safeguard the fish population.  

2. Theory of Natural Selection

It is the process that help in enhancing the success rate of adaptation of the organisms to their environment. To do this, organisms reproduce with a number of variations in its genotype and phenotypes. Natural selection can be accidental or by choice. Variations in the genotype can increase the organism’s chances of survival and such tendancey is preserved and continued from one generation to another in an accelerating manner. A positive evolution is a process,  often occurs as a consequence of natural selection. Therefore, higher the potential for natural selection, better the rate of survival, development and progression of organisms through generations. Therefore, natural selection is the main stream of evolutionary process in which organisms that are more adapted to their environment are more likely to survive and pass on the genes that aided their success. This process causes species to change and diverge over time

3. Survival of the Fittest

According to this law, greater the fitness of an individual, better the survival rate and this is the reason different organisms are placed at different levels of their pyramid. Fitness is the reason behind some species are still existing(stronger or fitter ones)  but a few species have gone into extinction ( weaker ones). Browse here For more information.


Concept of Speciation

A group of organisms with similar features are called species. Species interbreed to evolve their generation. Speciation is the process of origin of a new species and the 2 major mechanisms behind the speciation are genetic drift and microevolution. The evolution of new species due to the geographical segregation is called genetic drift. Genetic drift carries a positive effect when a species intermingled with similar species of another geographic location. On the other hand, microevolution is a small scale version of evolution leading to the benefit of organisms . For instance, change in the body colour of beetles over a period that helped them in many ways.


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 many 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 fall under the class Mammalian but not all mammalians are highly diffrent instead, they resemble insome ways. For instance, mammalians encompass a variety of animals such as monkeys, chimps, elephants, and cows, etc because they all resemble humans in some interests . SOme of the similarities are eyes, fingers, toes, body hair, however thay cannot interbreed. 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 (same) is the similarities inherited by two organisms from their common ancestor. Organs such as wings of a bat, hands of human beings, wings of birds, flippers of seals, forelimb of a horse, etc, have a common fundamental anatomy . However, each organisms use these structures for different purposes. For example, horses use their forelimbs for running, human beings use forelimbs (upper limb) for working but whales use their flippers for swimming. 


Homologous organs-image from  www.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 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.


Read more


Evidences For  Evolution 


Introduction to evolution


Accumulation of variations


Convergent and divergent evolution

5 .

Adaptive radiation




  1. Give an example of how fossils helped din proving as the evidence of evolution

  2. Give 2 examples of homologous organs and explain.

  3. Name the highest and lowest taxa while classifying the organisms.

  4. Explain the principles of Darwinism.

  5. A fish produces so many eggs but only few of the eggs become offspring,  which of the Darwin's principles are applicable here.




Course List