Evolution is not completely understood by many. Many people believe that higher organisms “evolve” from lower beings – the bacteria being the lowest in the evolutionary chain to man being the highest. This is a common mistake.
It was Charles Darwin who proposed the theory of common descent which suggests that all living organisms on Earth have a common ancestor. Darwin, during his studies on the Galápagos Islands, observed several species of finches that seemed closely related to each other, but differed only in the shape of their beaks. Darwin surmised that the different beak shapes naturally evolved as a response to the kinds of food that were available in the island. Finches with large beaks feasted on nuts which they opened with their big beaks, whereas insect-eating finches had narrow beaks which helped them pull the grub out of small holes.
So what exactly is evolution?
Evolution is the process of small changes in the gene pool that happen over a long time.
Minute changes occur in the gene pool over millions of years, so most of evolution is not apparent to the human eye. But the evolution of the English moth (Biston Betularia) has actually been observed from 1848, and it shows us a glimpse of what evolution is really about.
Before 1848, moth populations were predominantly light in color. By 1898, it was observed that the moth population became predominantly dark. What caused the gene responsible for coloring to change?
This is an excellent example of natural selection. Because of the industrial revolution at the time, the trees that the moths alighted on used to be covered with soot. A light moth against this dark background was a dinner call for the birds who ate many of them. This resulted in light moths being eaten before they reproduced, and more dark moths surviving and reproducing. These offsprings had the dark coloring gene and they swelled in population.
It is to be noted that such changes do not occur within an individual of the population. Individuals retain the same traits or characteristics. In our moth example above, a light moth did not gradually turn dark. Rather, more dark than light moths survived, and the population as a whole evolved from light to dark.
Microevolution and Macroevolution
Change that occurs within a single species is called microevolution. The moths which changed from light to dark underwent microevolution. When a whole new species evolves, it is called macroevolution.
Evolutionary biologists have differing opinions on the mechanism of micro and macro evolution. Some argue that these two different types of evolutions happen in totally different ways, while others argue that macroevolution is just a total of all the microevolution that happened over millions of years.
The rich diversity of life that we see on Earth is a result of both micro and macro evolution. And as such, evolution is a fascinating field that all scientifically inclined people must look into to gain a better understanding of life.