The different forms of life present in the earth at this moment makes for a small fraction of all those that have inhabited our planet since life started around 3.7bn years ago. All those near infinite life forms are connected with one another by the chain of descent or of common origin. Although this notion itself was not new even in his time, Charles Darwin was the first person to systematically elaborate and justify the idea now popularly known as evolution by natural selection. In the book, ‘The Origin of Species’, published in 1959, he explains in great detail the exact mechanism by which the process takes place. It’s considered among the greatest and most beautiful scientific achievements of all time.
The first premise to understanding Darwin’s theory is that each living form struggles to survive and leave as many offspring as it can. A parent form produces offspring, not all of which are uniform. They may randomly and minutely vary in aspects like habits, constitution, and organization. If these differences are in some way favorable to the bearer, that form is likely to live longer and reproduce more of its kind. When many of such minute variations accumulate over a long period of time, the living forms can acquire different appearances from the parent form so as to appear unrelated to one another. Over a span of time, many such forms grow in complexity, occupying different places within the economy of nature, giving rise to an immensely vast number of species that we see populating the world.
It’s admirable to be able to state these principles with clarity especially at a time when the creationist dogma of Christianity that each species was separately created by God was what most people accepted unquestionably. However, Darwin goes many steps further and illustrates different aspects related to nature, contrasting between how those facts become unexplainable under the theory of creation and how they are naturally explained by the theory of natural selection.
One such interesting fact is that embryos of species which vary greatly during adulthood are much more alike. This fact is explained by the principle that major variations specified above occur in the species during the age when they are most active or when they are adults and are accordingly inherited at similar ages. Hence the embryo of various related species with common progenitors being alike is explained on the view of species arising through natural selection. However, if they were created separately the question as to why embryos of differently created species should have been so alike cannot be reasonably answered.
Various body parts of different species with widely different functions like the wings of birds, fins of fish and legs of dogs share common structure in the underlying bone indicating their common origin. Natural selection has taken a single raw material from a common parent and out of that, it has formed different organs that would be beneficial to different species in their respective environments by the mechanism of accumulating small variations over a period of time. Again, under the false belief of godly creation of different species separately, these structures remain unexplained.
Besides giving these and more explanations in great detail evidencing the power of natural selection, Darwin takes on many challenges posed against the theory and answers each of them. One such challenge is the fact of the same species appearing in geographical regions vastly far from each other without it being found in the intermediate regions giving the illusion of being created separately in two regions. This he explains by referring to the possible geological changes over the long course of history whereby it’s possible that different continents weren’t as separate in the past as it is now. That would have allowed species from one region to have migrated to another region after which the two regions separated. Migration has been a powerful force in populating the entire planet with different variations of life forms. There are many interesting ways life forms can migrate from one place to another. Seeds of plants can stick into the feet of birds which fly to faraway islands and drop it there unknowingly. Even more amazingly, when some fish swallows the seed of a plant and later some bird devours the fish then goes on a long flight to another distant island, often enough the seed still retains the capacity for germination after the bird regurgitates the undigested seed.
Even today, many people strongly oppose evolution by natural selection due to ideological biases or ignorance. Although the theory explains so many of the phenomena found in nature which are otherwise completely inexplicable, scientific evidence for it is overwhelming and so much of its predictions have come true. Few findings in the history of science would have had such a powerful impact paving the way for many further discoveries and progress. The Origin of Species is a great read for anyone who wants to reflect upon the diversity of life and wonders where it all came from.
