The notion where one type of organism can descend from another type dates back to the Pre-Socratic era. This idea carried itself into the Roman era and was evident in some of the scientific works from that period, such as the De rerum natura (Translation: On the Nature of Things) by the Roman poet and philosopher Titus Lucretius Carus.
Throughout this time period, there were no actual words which describe the process of evolution. However, there were rudimentary ideas and suggestions which hinted at the same, but in a much broader and generalized sense.
On the Origin of Species
The modern concept of evolution was proposed by Charles Darwin and was made renowned worldwide through his book, “On the Origin of Species” in 1859. The highlight of his work was that organisms, over a period of time, change as a result of behavioural or physical traits which are passed down from generation to generation. These changes enable an organism to better adapt to its environment and eventually pass on the traits to future generations. Those organisms that cannot adapt to change die out – hence the term “Survival of the fittest.”
From Land to Sea
One of the best examples that substantiate the process of natural selection is the evolution of whales. The very first ancestor of whales was a terrestrial, dog-like animal. In fact, Darwin even proposed the idea that the evolution of whales began with organisms that had terrestrial origins. In his book, he even provided a hypothetical example of a black bear that could, over time, gradually evolve into an animal as big as a whale under the select circumstances and factors.
Darwin quoted:
“I can see no difficulty in a race of bears being rendered, by natural selection, more aquatic in their structure and habits, with larger and larger mouths, till a creature was produced as monstrous as a whale.“
However, Darwin’s idea was ridiculed at that time because it went against so many established ideologies and beliefs. The controversy that he stirred became so much that this section was removed from later editions of his book.
Today, scientists knew that Darwin was on the right track, but he had not provided the most relevant example. Had he taken examples of hippos or cows, he may have had more success (cows, hippos and whales actually belong to the same order – Artiodactyla, making these animals unlikely relatives).
Also Read: Bergmann’s rule
Natural Selection
Natural selection is a key mechanism of evolution. It states that the organisms that are well-adapted to the environment have more chances of survival and are likely to pass on the traits that aided their survival.
One of the most important concepts in biology, natural selection describes how an organism adapts to its environment. Natural Selection can lead to the process of evolution, where a group of organisms with certain characteristics have a much higher chance of survival than other groups. These successful group of organisms pass on their inheritable characteristics to their offsprings.
A classic example of natural selection in action is the pepper moths. Prior to the industrial revolution, lichens were quite abundant and covered the barks of many trees. The pepper moths that rested on these trees had light coloured patterns on its body and wings. This gave them adequate camouflage and hence, was able to blend in with the trees and escape predation.
However, during the industrial revolution, the pollution killed off the lichens and darkened the trees with soot. This made the bark of the trees very dark. Consequently, when moths these rested on the trees, its light coloured body stood out prominent and became easy prey.
The moths that had darker wings and bodies were able to survive because they were camouflaged better. Eventually, the dark-coloured moths thrived as they were able to hide better against the dark barks of the trees. These dark coloured moths were also able to pass on the genes that helped them survive predation. Conversely, the light coloured moths became rarer until they were no longer found.
Also Read: Genetic Drift
LUCA – Ancestor of all Life
LUCA or the Last Universal Common Ancestor is an organism or a group of organisms from which all life that currently lives on earth has a common descent. LUCA is not the first organism to ever live, but one among the many. The true form of LUCA cannot be deduced from fossils, however, through phylogenetic bracketing, it has been inferred that LUCA is a unicellular organism – superficially similar to today’s bacteria.
LUCA was most likely an extremophile, living near the hellish volcanic vents of the ancient oceans. It was also autotrophic and anaerobic, meaning that it didn’t need oxygen to survive and could make its own food. From an evolutionary perspective, LUCA is a milestone for the inception of life on earth. Though life has diversified beyond comprehension, we can still trace evidence of LUCA’s existence in the genes of modern animals.
Evolution of Life on Earth
Throughout the earth’s 4.5 billion year history, many organisms have evolved and eventually gone extinct. In fact, studies have shown that more than 99% of all life that ever lived is currently extinct. The actual origin of life still remains a mystery. Microbial fossils are one of the earliest known fossils and it dates back to 3.4 billion years. However, scientists still theorize that life could have risen even earlier.
The current consensus about the origin of life is that life began from self-replicating molecules, which eventually made up the complex biochemistry of today’s life. The earliest form of these self-replicating molecules would have been precursors to RNA.
A few attempts have been made to explain the very first origins of life. Some of the more popular ones include:
- Miller Urey Experiment
- Abiogenesis
- Panspermia
- Clay Hypothesis
- Deep-Sea Vent Hypothesis
- RNA World Hypothesis
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