March for science

The word “Evolutio” was first used in classical Latin, meaning unrolling of a scroll, in early 17^th century and after that, often, it started to be applied to the process of unrolling, opening out, or revealing [1]. From 18^th till the second half of 19^th century, the term “Evolution” was used primarily in an embryological sense to designate the development of an individual embryo [2]. Today in biology, the concept of evolution covers the alterations inherited in organisms from generation to generation in a long time-period.

One of the first comprehensive theory of evolution was proposed by a French naturalist, Jean Baptiste Lamarck, in 1801. He proposed a theory of evolution that mainly argued that the life was not stagnant, but organisms kept changing their behavior with altering environment, in order to survive. He believed that simple life forms get originated from spontaneous generation continuously, and an innate force (sometimes described as nervous fluid) drives the complexity in the organisms over time.

Darwin’s theory of evolution had two main points. First, diverse group of animals evolve from a common or a few common ancestors. Second, the process of evolution occurs by natural selection. The mechanism of natural selection is based on four principles:

1. Variation: In a population, individuals have variation in appearance and behavior. Variations include hair texture or color, body size, facial features etc.

2. Inheritance: Some features or traits are passed consistently from parents to offspring. These are heritable traits, whereas other traits get influenced by the surrounding environmental conditions and are not heritable.

3. Population growth rate increment: In a population, growth rate increases to an extent which becomes challenging to be supported by the available nutrients. Due to this scarcity of nutrients, each generation goes through a significant mortality rate.

4. Differential survival and reproduction: The individuals with the traits that are well suited to be fit and survive better in the struggle for nutrients would contribute more offspring to the next generation [4].

As mentioned before, Alfred Russel Wallace also came up with the similar theory of evolution as Darwin’s, but there were some subtle differences. Also, Lamarck had few common points but very distinct differences from Darwin’s idea of evolution. In order to understand the distinctions between these theories, a brief comparison is done below.

Darwin vs Lamarck’s theory of evolution

Darwin’s theory of natural selection explained the change in the organisms through natural variations, whereas Lamarck explained the changes based on the usage of an organ. According to Darwin, everyone was slightly different from one another, and these variations made some organisms more fit to survive and reproduce in comparison to others (survival of the fittest). These features of an organism, that are responsible for the fitness to survive, got more likely to be passed to generations. For example, in case of Giraffe, Darwin’s theory would state that longer necked Giraffe were more likely to survive because they could eat leaves from taller trees. Therefore, this long neck feature was favored and passed to the next generations, and long-necked Giraffe became fit to survive [6]. Whereas, as explained before, Lamarck’s theory suggested that if a Giraffe stretched its neck for leaves, a "nervous fluid" would flow into its neck and make it longer. Its offspring would inherit the longer neck and continued stretching would make it longer over several generations.

Lamarck described the evolution by increasing complexity, whereas Darwin proposed the concept of differential survival. In support of Lamarck´s transmission of acquired characteristics through generations, Darwin explained the inheritance of the characteristics (later, understood as inheritance of genes). The characteristics carried during an individual’s lifetime do not get simply passed to their offspring; for example, if someone pierces their ear, it does not mean that their children will be born with pierced ears. Darwin’s theory became strengthened when after many years of his demise, the study of genetics got famous. Darwin did not know what genes and alleles are. Genetics showed that all inherited traits were passed on through genes, which are unaffected by outside world and are naturally varied, as Darwin predicted (although, today, epigenetic has shown that genes could be silenced or activated by epigenetic marks like methylation or acetylation based on eating habits or drug or chemical exposure etc., but could not be inherited to the next generation, unless it gets imprinted in the gene, which is a very rare and still debatable phenomenon). Though Darwin didn't know what genes are, he could see their effect on natural selection [7].

At last, Lamarck didn’t mention about extinction whereas Darwin's theory explained the process of extinction, where the fittest survives and the weakest keeps getting endangered and finally might get extinct [8].

The next most important conflict of views between these eminent scientists was related to the subject of sexual selection through female choice. Darwin's theory of sexual selection consisted of two distinct parts. First, the combats between males (common among polygamous animals and birds) and second, the choice of females for more musical or more ornamental male birds. The combats of males is an observed fact and the development of weapons such as horns, canine teeth, spurs, etc., is a result of natural selection acting through such combats. The selection of male birds by females is an inference from observed facts. Wallace accepted the first part, but he was skeptic about the second part which is the selection of males by female choice, based on aesthetic criteria. He hypothesized that bright colors and features of males are the characteristics of the species. Instead of female choice, the ecological surrounding might lead to natural selection. For example, he tried to explain the dull, cryptic coloration of the females based on her activity. According to him, female dull color could be explained by the fact that in majority of cases, female incubates the eggs. Therefore, bearing cryptic color is advantageous for her to escape from predators. In support of this explanation, the sexual dimorphism is reversed in the case of Cassowaries, where males incubate the eggs and therefore are less brightly colored. Females are bigger and more brightly colored [9].

Another difference of standpoint between Darwin and Wallace was on the presence of arctic (polar region located at the north-most part of the world) plants in the southern hemisphere and on isolated mountaintops within the tropics. Darwin accounted for the phenomenon by cooling of the tropical lowlands of the whole earth during the glacial period to such an extent as to allow large numbers of north temperate and arctic plants to spread across the continents to the southern hemispheres, and as the cold passed away to ascend to the summits of isolated tropical mountains. Wallace explained the difficulties in Darwin's view as twofold, mentioned below.

First, lowering temperature of inter-tropical lowlands to the required extent would inevitably have destroyed much of the overwhelming luxuriance and variety of plant, insect and bird life that characterize those regions. According to Wallace, Darwin could have had no conception of its wonderfully rich and highly specialized fauna and flora. In the second place, even if a sufficient lowering of temperature had occurred during the ice age, it would not account for the facts that involve, as Sir Joseph Hooker remarks, a continuous current of vegetation from north to south, going much further back than the glacial period. Because, it has led to the transmission not of existing species only, but of distinct representative species, and even distinct genera. This shows that the process must have been going on long before the cold period [10].

Evidences for Darwins theory of evolution

Although the original hypothesis from Darwin has been modified and expanded extensively, the core concepts remain same. Darwin’s time was not equipped with Genetics and molecular biology tools. He observed the pattern of evolution, but he didn't really know about the mechanism. That came later with the advancement in Genetics and molecular biology, with the discovery of how genes encode different biological and behavioral traits, and how genes are passed down from parents to offspring. The physical and behavioral changes that make natural selection possible happen at the level of DNA and genes. Such changes are called mutations. Mutations can be caused by random errors in DNA replication or repair, or by chemical or radiation damage [11]. Genetic mutants are events by chance, which might be advantageous or disadvantageous for an organism to survive. But if a gene variant improves adaptation to the environment, the organisms carrying that gene are more likely to survive and reproduce than those without it. Over time, their descendants will tend to increase, changing the average characteristics of the population. In this way, natural selection guides the evolutionary process, preserving and adding up the beneficial mutations and rejecting the bad ones. Although the genetic variation on which natural selection works is based on random or chance elements, natural selection itself produces “adaptive” change- the very opposite of chance. Also, genes evolve at different rates because, although mutation is a random event, some proteins are much more tolerant of changes in their amino acid sequence than others. Due to this reason, genes that encode these more tolerant, less constrained proteins evolve faster.

Many researchers have found fossil records that are convincing evidence for biological evolution. In 1799, William Smith reported that in uninterrupted layers of rock, fossils occurred in a definite sequential order, with more modern-appearing ones closer to the top. His findings were confirmed and extended in 1830s by the paleontologist William Lonsdale, who recognized that fossil remains of organisms from lower strata were more primitive than the ones above. Still, a lot of connections were missing at that time, in order to provide a concrete evidence for the biological evolution. Today, the researchers have filled many gaps in the paleontology record. Thousands of fossil organisms found in the fine-dated rock sequences represent successions of forms through time and manifest many evolutionary transitions. Below is a list that provides the order in which increasingly complex forms of life appeared with time [12]:

Also, the inferences form paleontology data got reinforced by comparative anatomy analysis. For example, the skeleton of humans, mice and bats are strikingly similar. The correspondence between these animals can be observed in every part of the body including the limbs. These homologies in the structures are best explained by common descent. Not only this, similarities during development from an embryo to adult among the organisms also give an independent evidence for common descent. For example, Barnacles are sedentary crustaceans with little apparent similarity to other crustaceans as Lobsters, Shrimps or Copepods. Yet Barnacles pass through a swimming larval stage in which they look like other crustaceans’ larvae. The similarities of larval stages support the conclusion that all crustaceans have homologous parts and a common ancestry. Similarly, a wide variety of organisms from fruit flies to worms to mice to humans have very similar sequences of genes that are active early in development. The presence of such similar genes doing similar things across such a wide range of organisms is best explained by their presence in a very early common ancestor of all these groups.

Evidences from molecular biology again reinforce the unifying principle of common descent. The code used to translate nucleotide sequence into amino acid sequences is essentially the same in all organisms. Proteins in all organisms are composed of the same set of 20 amino acids. This unity of composition and function is a powerful argument in favor of common descent of the most diverse organisms.

Human evolution is also evident with the advancement in the field of evolutionary biology. Studies in evolutionary biology have led to the conclusion that human beings arose from ancestral primates. Many fossil-records document the time and rate at which primate and human evolution occurred. A great number of fossil specimens cannot be assigned to the modern Homo sapiens. These specimens have been well dated, often by means of radiometric techniques. They reveal a well-branched tree, parts of which trace a general evolutionary sequence leading from ape-like forms to modern humans. Molecular biology also has provided strong evidence of the close relationship between humans and apes. Analysis of many proteins and genes has shown that humans are genetically similar to Chimpanzees and Gorillas and less similar to Orangutans and other primates [12].

Contribution of evolutionary biology to other fields of science

Some of the direct practical applications of the theory of evolution are mentioned below. These are few examples of the vast applications found in today’s world.

Production of novel anti-microbial medicines to fight against gradually evolving pathogens: Pathogens are those microbes that have the capability to infect humans. There have been numerous microbial deadly infection outbreaks in the past, and it keeps happening in the present, for example Hepatitis A, Bubonic plague, Salmonella infections, Marburg Hemorrhagic Fever, Cholera, Avian influenza, Swine flu, Nipah, etc. It’s very important to understand the evolution of the microbes in order to fight against pathogenic outbreaks. More importantly, microbes develop resistance against couple of antibiotics as a result of point mutations in the pathogen gene. Those microbes, which gets mutation and survive after antimicrobial treatment, lives on to reproduce and pass their traits to their offspring. That finally results in a fully resistant colony. Pests evolve resistance to the drugs and pesticides used against them. To have better pest control, evolutionary theory is also used in the field of resistance management in agriculture [13].

Finding novel genes required for constructing a body part or specific types of cells: Understanding the changes that have occurred during organisms’ evolution can reveal the genes needed to construct parts of the body or also the genes that may be involved in human genetic disorders. For example, comparing the genome of Antarctic Icefish, which lacks red blood cells, to its close relatives like Antarctic Rockcod revealed the genes needed to make these blood cells [14]. Another example is of the Mexican tetra (an albino Cavefish) that lost its eyesight during evolution. Breeding together different populations of this Blindfish produced some offspring with functional eyes, since different mutations had occurred in the isolated populations that had evolved in different caves [15]. This helped in identifying the genes required for vision and pigmentation, like crystallins and melanocortin 1 receptor [16].

Application in farming and evolution by artificial selection rather than natural selection: Artificial selection is a major technological application of evolution and is a mimic of Darwin’s theory of natural selection. It’s the intentional selection of certain traits for the benefit of humans in a population of organisms. Humans have used artificial selection for thousands of years in the domestication of plants and animals [17]. Based on the choices made by humans, some varieties of plants are more favored than the others in the same family. In this case, the best choice by the consumers is selected by the farmers. That choice is produced in most quantities and hence becomes so called “fittest by man’s choice”.

Artificial selection has also become a vital part of genetic engineering, with selectable markers such as antibiotic resistance genes being used to manipulate DNA in molecular biology. It’s also possible to use repeated rounds of mutation and selection to evolve proteins with particular properties, such as modified enzymes or new antibiotics, in a process called directed evolution [18, 19].

Social impact of Darwin’s theory of evolution

Darwin grew up in Britain and studied theology. He followed Christianity since childhood as a religious practice with his family. A single opportunity of traveling in HMS Beagle to study plants and animals at Galapagos Islands changed his life; his frame of thoughts took him from theism to atheism. His observations made a revolution in understanding biological and social interactions between different species. Darwin’s publication “On the Origin of Species” in 1859 was one of the most logical and comprehensive explanation of our origin without any belief on fairy tales, alienism and without reference to God. Although, it was not the first time that a naturalist view point of evolution was discussed. The naturalist explanation for the origin of life were existing even before Darwin, but Darwin’s compilation of his observations from nature was revolutionary and soon became famous amongst naturalists.

In 1872, Darwin published “Descent of Man” where Darwinism was applied to morality. It explained that Man, like every other animal has advanced to his highest condition through a struggle for existence and has evolved from ancestors. This directly opposed the idea of Christianity where Man was the center of creation. The obvious reason for this idea to become controversial was that it was unacceptable to Christian faith and it was a direct attack to the believes in Christianity. It was accepted among the scientists. Eliminating God from science made room for strictly scientific explanations of all-natural phenomena; it gave rise to positivism (a philosophical theory stating that certain "positive" knowledge is based on natural phenomena and their properties and relations. Thus, information derived from sensory experience, interpreted through reason and logic, forms the exclusive source of all certain knowledge [20]); it produced a powerful intellectual revolution, the effects of which have lasted to this day. ​

Similar to the religious belief of Man being the center of creation by God, many theologians and philosophers believed that Man was a creature above and apart from other living beings. Because of this belief and Man being considered superior or of prime importance, contemporaries found most difficult to accept Darwin’s theory of common descent of Man. Aristotle, Descartes and Kant agreed on this sentiment of man being of prime importance, no matter how else their thinking diverged. But biologists Thomas Huxley and Ernst Haeckel revealed through rigorous comparative anatomical study that humans and living apes clearly had common ancestry, an assessment that has never again been seriously questioned in science. The application of the theory of common descent of Man deprived man of his former unique position.

Ironically, these events did not lead to an end to anthropocentrism (human-centered point of view). The study of man showed that, despite his descent, he is indeed unique among all organisms. Human intelligence is unmatched by that of any other creature. Humans are the only animals with true language including grammar and syntax. Only humanity, as Darwin emphasized, has developed genuine ethical systems. In addition, through high intelligence, language and long parental care, humans are the only creatures to have created a rich culture. And by these means, humanity has attained an unprecedented dominance over the entire globe. Darwin introduced a concept of population thinking where all groupings of living organisms, including humans, are populations that consist of uniquely different individuals. No two out of entire human race are the same. Darwin introduced the implication of historical findings into scientific thinking to explain evolution. He accepted the universality of randomness and chance throughout the process of natural selection. Despite the initial resistance by physicists and philosophers, the role of chance in natural processes is now almost universally acknowledged.

Darwin provided a scientific foundation for ethics. The question is frequently raised, as to whether evolution adequately explains healthy human ethics. A question prevails, that if selection rewards the individual only for behavior that enhances his own survival and reproductive success, then how such pure selfishness can lead to any sound ethics? The widespread thesis of social Darwinism, promoted at the end of the 19th century by Spencer, was that evolutionary explanations were at odds with the development of ethics. We now know, however, that in a social species not only the individual must be considered, but an entire social group can be the target of selection. Darwin applied this reasoning to the human species in 1871 in The Descent of Man. The survival and prosperity of a social group depends to a large extent on the harmonious cooperation of the members of the group, and this behavior must be based on altruism. Such altruism, by furthering the survival and prosperity of the group, also indirectly benefits the fitness of the group’s individuals. The result amounts to selection favoring altruistic behavior. Such selection for altruism has been demonstrated in recent years to be widespread among many other social animals (like ants and honey bees). One can then perhaps encapsulate the relation between ethics and evolution by saying that a propensity for altruism and harmonious cooperation in social groups is favored by natural selection. The old thesis of social Darwinism, strict selfishness, was based on an incomplete understanding of animals, particularly social species.

Perhaps, Darwin’s greatest contribution was that he developed a set of new principles that influence the thinking of every person. The living world, through evolution, can be explained without recourse to super naturalism. We must adopt population thinking, in which all individuals are unique, which is vital for the progression of education and the refutation of racism. Natural selection, applied to social groups, is indeed enough to account for the origin and maintenance of altruistic ethical systems in a society or whole human civilization; to borrow Darwin’s phrase, "there is grandeur in this view of life”. New modes of thinking have been, and are being, evolved. Almost every component in modern man’s belief system is somehow affected by Darwinian principles [21].

Darwin’s theory gave strength to the dialectical materialistic theories of Marx. When Marx studied Darwin’s theory, he was so excited about it, especially its implications in understanding historical need for the emergence of religions and their reactionary roles in present society, that he wrote to his colleague Friedrich Engels that Darwin’s work “contains the foundation in natural history for our view.” While Marx and most early Marxists adopted some elements of Darwinism with alacrity, most of them rejected natural selection, especially when applied to humans. ​

Darwin’s theory also had some negative social impacts specially because of the wrong or incomplete interpretation of his theory. In 1883, Francis Galton coined a term “Eugenics”, which is a set of beliefs and practices that aim at improving the genetic quality of a human population by selection. These practices do not allow physically and mentally handicapped or people carrying genetic diseases to reproduce. Eugenics researchers aimed to control human mating to cease the propagation of disease genes or the efficient propagation of the fit genes. In this way, they tried to control the reproduction between people in populations, which was of course debated for being ethical. Their viewpoint was that breeding of fittest human races continuously would lead to better evolved human population. A major criticism of eugenics policies is that, regardless of whether "negative" or "positive" policies are used, they are susceptible to abuse because the criteria of selection are determined by whichever group is in political power at the time. Furthermore, negative eugenics is considered by many, to be a violation of basic human rights, which include the right to reproduction. Another criticism is that eugenic policies eventually lead to a loss of genetic diversity, resulting in inbreeding depression due to lower genetic variation.

Darwin’s survival of fittest is taken to an extreme, that war between men were justified based on his theory of survival of fittest. Herbert Spencer gave a theory, mentioning that societies which are more fit to survive, survive better and longer than the ones which are unfit. There was moral justification provided by Socio-Darwinism when Europeans colonized other societies which were not as strong as Europeans. Also, as they kept winning, they considered themselves superior based on survival of fittest and as their survival was getting prominent after wars, they developed the idea of being superior. It all made sense. In practice, the idea of natural selection (although selection of a population based on war is not a way of natural selection, instead its man driven artificial selection) by getting into war and winning, became a reality in the societies conquered by Europeans. Hitler followed the idea of survival of the fittest and considering Jews to be less evolved. He justified his ruthless actions to wipe out Jews so that his race does not get mixed with the less evolved Jews [21].

Evolution is a proven fact, not a myth

Some creationists argue that “no one has seen evolution to occur”. This misses the point about what is science and how science tests its hypotheses. We do not see Earth going around the Sun or the atoms that make up matter. We see their consequences. Scientists infer that atoms exist and Earth revolves because they have tested predictions derived from these concepts by extensive observation and experimentation [12].

Evolution is a phenomenon that happens in the timescale of thousands of years. Therefore, it’s difficult to observe evolution on large scale in one's lifetime. But, due to the amazing evolutionary achievement of humans to be able to read, write and pass on information from generation to generation, we now know that evolution is a fact, not a belief. There have been various archaeological, genetic and molecular biology research findings in support of the Darwin´s theory of evolution (as explained before), which makes it the most accepted theory until now. Darwin's theory lacked certain evidences to support his observations. The missing links in Darwin’s theory have been filled over time with the help of amazing works done by thousands of researchers. Also, Darwin’s observation and inferences are commendable keeping in mind the time when he proposed his theory without having an idea about genetics and minimal availability of archaeological data. In the end, a quote from Darwin’s book “The origin of species” reinforces the concept of evolution, beautifully:

“Thus, from the war of nature, from famine and death, the most exalted object which we are capable of conceiving, namely, the production of the higher animals, directly follows. There is grandeur in this view of life, with its several powers, having been originally breathed into a few forms or into one; and that, whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been and are being evolved.” ― Charles Darwin, The Origin of Species

*Dr. Madhulika Rai is post-doctoral researcher, in the field of metabolism and developmental biology, working in Indiana University, Bloomington, USA.

References

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