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Sukanya Ramani, Research Associate, Department of Biology, Prayoga, Bengaluru
sukanya@prayoga.org.in
Understanding the theory of evolution is an excellent way for students to learn the process of scientific inquiry. The question of how so many different species of organisms came into existence on earth has been boggling the minds of scientists and philosophers since time immemorial. Starting from speculating what the first organisms were to the process by which the current organisms populated the earth, various theories have been put forth. Some philosophers even thought that the first organisms that came on earth were an interplay between fire, water, earth and air! [1] The most widely accepted theory is evolution by natural selection, as suggested by Charles Darwin [2] and Alfred Russell Wallace.
Nature “selects” individuals best adapted to an environment
Different organisms have their origins in pre-existing life forms and the observable differences are due to the changes over many generations. This is known as evolution [3]. Earth is inhabited by around 10 to 30 million species out of which only two million have been discovered till date. The diversity in life forms is due to evolution. All organisms have a common ancestor that lived many millions of years ago. In his famous book, On the Origin of Species, Charles Darwin explains, among other things, as to how evolution occurs and the reasons for the presence of different organs in organisms such as the wings. He suggested that specific characteristics are selected, which favour successful survival of individuals of a particular species in an environment. This explanation might not have been supported by enough evidence at Darwin’s time, but with growing fossils records (Figure 2 and 3) and other areas of biology such as biochemistry, genetics and molecular biology, evolution has proven to be a fact indeed.
Figure 1: Evolutionary tree sketched by Charles Darwin
Figure 2: Growing fossil record proves that evolution by natural selection is indeed a fact
Figure 3: A fossil of Archaeopteryx, a bird that lived about 150 million years ago and had many reptilian characteristics, was discovered in 1861 and helped support the hypothesis of evolution proposed by Charles Darwin in The Origin of Species two years earlier.
Misconceptions of Evolution
Evolution by natural selection is pivotal in biology, yet it is rife with misconceptions. Some of them are as follows:
“Evolution talks about the origin of life”
Although the theory of evolution speculates how life on earth originated, that does not form the basis for explaining the theory. Instead, evolution is all about how life might have changed and diversified after the origin of life.
“Evolution happens only gradually”
A common misconception of evolution is that it happens very slowly. Let us take example that can disprove this statement. Wall lizards that were transported from one island to another developed new features within a mere 36 years! [4] These lizards that originally fed on insects in their previous habitat fed on plants in the island in which they were introduced. This was confirmed by the morphological differences in the heads of lizards from both the islands (Figure 4).
Figure 4: Lizards from the two islands, Pod Kopiste and Pod Mrcaru [5]
Another interesting example is of the tusk sizes in elephants in Uganda. Poaching of elephants for their enormous tusks was a common occurrence. Over time, as the large tusked elephants got wiped out, elephants with small tusks increased in number (Figure 5). Here are two examples of evolution happening before our very eyes! [5].
Figure 5: Elephants that had long tusks were poached, thus decreasing in number, while the smaller tusked elephants increased in number [6]
“Evolution is progressive and organisms get better with time”
Individuals that are a product of natural selection do not have characteristics that are exactly suited to the environment. Traits that are useful in one environment may be detrimental in another. Evolution is not a ladder where humans are at the top, it is rather a tree with branches of different species. All organisms are cousins and have a common ancestor.
Scope of evolution in understanding various biological concepts
Evolution, the misunderstood concept that it may be, leads to a better understanding of the different biological concepts. The teaching of evolution also has great practical value for students. Evolutionary biology, directly or indirectly, has made numerous contributions to society. Let us look at a few examples for clarity.
Many harmful bacteria have been a cause of worry for humans. Many of them have become resistant due to continuous usage of antibiotics. This is because of natural selection acting on the naturally occurring genetic variation in bacteria. When antibiotics are ingested by humans it leads to some bacteria in the population being resistant to the antibiotics and hence are able to multiply rapidly. When antibiotics are taken beyond what has been prescribed, the useful bacteria also tend to die.
Living organisms are adapted to their environment. This means that the different characteristics that they possess make them suited for survival in an environment. For example, polar bears live in cold climatic conditions. Their adaptations include a thick fur that covers a layer of fat. Under the white fur, which helps in camouflage, they have black skin that soaks up the warming rays of the sun.
Evolution has also played an important role in changing the planet's physical environment through billions of years that life has been on earth. Let us take the example of photosynthesis, which is a product of evolution. Green plants take in carbon dioxide and water, produce organic compounds, and release oxygen. This has helped maintaining an atmosphere rich in oxygen. The weather and the movement of water among the atmosphere, land and oceans are also affected by living communities. Understanding evolution combines concepts from physics, chemistry, geology and other areas of science. Therefore, evolution is pivotal in understanding the world [3].
Random changes in the genetic composition, known as mutations is an important factor that leads to individuals having new characteristics. Rapid evolution also seems to be happening in organisms other than microscopic organisms. For example, plants have been shown to be resistant to toxic metals and do not seem to interbreed with the neighbouring plants that are non-tolerant. This is an example of evolution in action and this helps in the design of new technologies to protect crops from insects and disease.
Evolution seems to produce organisms that are so perfectly designed that the imperfections are not observed. There is a nerve called recurrent laryngeal that is present between the brain and the larynx (voice box). So, one would expect the nerve to travel directly from the brain to the larynx. Interestingly, in humans this nerve, goes down the chest, loops around one of the main arteries in the heart and then goes back into the larynx (Figure 6). This is a detour that could have been avoided. This is seen in all four-legged animals including giraffes! This nerve evolved first in fish like creatures where it directly travelled from the brain to the precursor of the larynx, the gills, near the heart. Some blood vessels (called the aortic arch) were also present along the gills and connected the heart. Over millions of generations, body shapes changed, animals grew necks moving further away from the heart and this nerve remained behind the embryonic vessel that became the aortic arch. This is exactly what we would expect from the accidents of history.
Figure 6: The nerve that travels down the brain, loops around the heart and goes back up into the larynx, a product of evolution [7]
Studies have shown that organisms that are in a specific embryonic stage look alike. Different cells in this embryonic stage are triggered by chemicals that act like switches to signal the production of certain characteristics. Recent research has revealed that these switches act similarly in different organisms even though they are separated by millions of years of evolution.
Why is it important to teach evolution?
Understanding evolution is critical for understanding biology. It is the only scientific explanation for the diversity of life. It explains the striking similarities among vastly different forms of life, the changes that occur within populations, and the development of new life forms. Excluding evolution from the science curricula or compromising to teach deprives students of this fundamental and unifying scientific concept to explain the natural world. Also, evolution presents diverse examples of how scientists collect and interpret evidence, test conflicting theories, and finally reach a consensus on the reasons for natural phenomena. In order to make informed decisions, understanding science is necessary and has become increasingly important for creativity and productivity in the workforce of the 21st century. Therefore, it is important that students receive science education that includes evolution.
Those who oppose the teaching of evolution often say that evolution should be taught as a "theory, not as a fact." Theories are understandings that develop from extensive observation, experimentation, and creative reflection. They incorporate a large body of scientific facts, laws, tested hypotheses, and logical inferences. In this sense, evolution is one of the strongest and most useful scientific theories we have.
In conclusion, evolution subject is key to understanding different biological concepts and the reason for the existence of vast diversity of life around us. Removing evolution from the science classroom or allowing it to be compromised will undermine the understanding of how scientific knowledge is amassed.
References:
1. Evolution and Paleontology in the Ancient World. https://ucmp.berkeley.edu/history/ancient.html (Accessed on 24.10.2020)
2. Desmond A. J., https://www.britannica.com/biography/Charles-Darwin (Accessed on 26.11.2020)
3. National Academy of Sciences (US). Working Group on Teaching Evolution. Teaching about evolution and the nature of science. Joseph Henry Press. 1998.
4. Herrel. et. al., Rapid large-scale evolutionary divergence in morphology and performance associated with exploitation of a different dietary resource, Proc Natl Acad Sci U S A, 2008, 105 (12), 4792–4795
5. Dawkins, R. The greatest show on earth: The evidence for evolution. Simon and Schuster. 2009.
6. Beardsley B., https://sites.google.com/site/greatestshowillustrated/chapter-05-before-our-very-eyes (Accessed on 22.11.2020)
7. "File: Recurrent laryngeal nerve.svg" by Jkwchui is licensed under CC BY-SA 3.0
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