Science and evolution (2024)

Abstract

Evolution is both a fact and a theory. Evolution is widely observable inlaboratory and natural populations as they change over time. The fact that weneed annual flu vaccines is one example of observable evolution. At the sametime, evolutionary theory explains more than observations, as the succession onthe fossil record. Hence, evolution is also the scientific theory that embodiesbiology, including all organisms and their characteristics. In this paper, weemphasize why evolution is the most important theory in biology. Evolutionexplains every biological detail, similar to how history explains many aspectsof a current political situation. Only evolution explains the patterns observedin the fossil record. Examples include the succession in the fossil record; wecannot find the easily fossilized mammals before 300 million years ago; afterthe extinction of the dinosaurs, the fossil record indicates that mammals andbirds radiated throughout the planet. Additionally, the fact that we are able toconstruct fairly consistent phylogenetic trees using distinct genetic markers inthe genome is only explained by evolutionary theory. Finally, we show that theprocesses that drive evolution, both on short and long time scales, areobservable facts.

Keywords: evolutionary theory, science, scientific method, scientific theory, macroevolution

In recent years, the teaching of creationism within science curricula has become asubject of public debate worldwide (Miller etal., 2006; Reiss 2011).Most of the attention has been given to cases in the United States of America (Jackson et al., 1995; Berkman and Plutzer, 2011; Baltzley, 2016; Ross, 2017),where many bills have been submitted to the Houses of Representatives encouragingteachers to express their criticism about evolution. In more serious cases, such asTurkey, evolution has recently been removed from the high school curriculum (Kingsley, 2017), and in Brazil, intelligent designresearch has recently reached university level (Silva,2017). The rise of “anti-vaxxers” and “flat-earthers” openly demonstratesthat the anti-science movement is not confined to biology, with devastating consequencessuch as the vaccine-preventable outbreaks (Milleret al., 2015). At the same time, the anti-sciencedebates have been usually promoted by anti-scientists and have stayed marginal toscientific literature. This explains the rising trend and confirms the need forscientists to hastily step into the scene. With this in mind, we felt compelled toaddress basic aspects of science and of the scientific method in the evolution versusdivine creation debate in a scientific journal.

Science can be defined as being both the criterion for gathering scientific data(scientific method), as well as the explanatory theories that were developed followingits criteria (scientific knowledge) (Project 2061American Association for the Advancement of Science, 1993; Roberts 2007). A few centuries ago, scientistsdecided to select a small part of human knowledge to restrict the method used toassemble this knowledge. The use of the scientific method does not mean that this ismore valuable than other types of knowledge; it is just more reliable in uncoveringnatural laws (Atkins, 1995).

One should regard science as a process in which scientists formulate hypotheses toexplain certain facts and to test their predictive models by confronting theirpredictions with new facts (Gilbert, 1991). Afact is something that we observe. For instance, when we drop an object, it falls to theground. This is a fact. The scientific theory that explains why objects fall is thetheory of gravity. A valid scientific theory can never become afact (Gould, 1981), as there is always thepossibility that a future explanation will better match newly discovered facts.

Evolution as a fact and theory

Evolution is a population concept. An individual does not evolve; only populationsevolve in the face of the genetic changes accumulated from one generation to thenext. The flu virus evolves. This explains why last years’ flu vaccine does not workon the current strain of the virus: only the resistant strains of the virus survivedlast year’s vaccine application. This is a textbook example of evolution by naturalselection. Genetic modifications are encountered in the resistant strains; thus,evolution is a fact (Gould, 1981). Mutation,migration, natural selection, and genetic drift are the evolutionary forces thatdrive genetic changes of natural populations from one generation to the next. Thisis known among biologists as microevolution.

On the other hand, evolutionary theory explains more than those facts that we canroutinely observe. This makes it a theory, but is it just a theory?The word theory has distinct meanings in science and in laylanguage (Ghose, 2013). A scientific theoryis the utmost position an idea may reach in science. Outside of academia, however, atheory is equivalent to a hypothesis, an idea that explains facts but has never beentested (Futuyama and Kirkpatrick, 2017). Thisoccurs because there seems to be no need for a distinction between hypothesis andtheory outside the scope of science. In science, however, this distinction isfundamental. An idea remains a hypothesis if it has never been confronted with new(independently collected) scientific data that would serve as a test for itspredictions. If a hypothesis has endured further testing by subsequent scientificexperiments, in time it becomes a valid scientific theory (Figure 1).

For any given valid scientific theory there are three possibilities. The firstpossibility is that the true explanation for the facts is entirelydifferent from the valid scientific theory. In this case, all scientific experimentsaimed to test the theory were flawed in design or in the interpretation of theresults. The second possibility is that the true explanation forthe facts is more restricted than the current scientific theory claims. In thiscase, the predictions of the theory agreed with newly collected data because alltests focused on a single (and true) aspect of the theory. Finally,the last alternative is that the true explanation for the facts isthe scientific theory. Science has the tools to reject (first alternative) and torefine (second alternative) scientific theories when they are confronted with newdata. However, even theories that endure many tests must still face these threepossibilities, as, even in light of the true explanation, sciencedoes not furnish us the tools to perceive truthfulness.

A hallmark of natural sciences is that scientific hypotheses and scientific theoriesmust make predictions about the natural world (Paz-y-Miño and Spinosa, 2011). Often, the older the theory, the morereliable it is because it has survived many empirical tests. Furthermore, the moreuniversal the theory, the more robust it becomes with time, as more tests would havebeen performed. According to Darwin, evolutionary theory is centred around twopoints (Darwin, 1859). First, from onegeneration to the next, natural populations change over time by a process of naturalselection. Second, all organisms have a common ancestor, and the time since thislast common ancestor lived is inversely proportional to the similarities that theorganisms will share today. Hence, evolutionary theory is universal because itincludes all (living and fossil) biological diversity and has implications for allheritable characteristics of life. Since 1859, evolutionary theory has become themost universal and, hence, widely tested of the scientific theories in biology.

Today, Darwin’s original theory has been refined, as he himself anticipated that itwould be (Darwin, 1871). This occurred in manyfronts because recent concepts, such as genetic drift and mutations, have providedmore details on how natural populations evolve. One example is theunderstanding that, at the molecular level, random evolution, rather than naturalselection, plays the most important role (Kimura,1991). This is known as the neutral theory, which completed its50^th anniversary in 2018.

The substance of Darwin’s original theory, however, remains. Theodosius Dobzhansky(1973) shared his astonishment that Charles Darwin proposed the theory of evolutionwithout many key biological concepts, such as that DNA is the molecule responsiblefor heredity. Half a century after Dobzhansky’s paper, it remains impressive thatthe theory of evolution still stands valid in light of the discoveries of themolecular biology revolution. Each newly sequenced genome tests some aspects ofDarwin’s theory, and, on each case, the sequence has been consistent with Darwin’sprediction of the shared evolutionary history of life. The sharp increase in scopeand universality of evolution has strengthened Darwin’s original proposal and madeevolutionary theory one of the most reliable and tested theories in the naturalsciences (National Academy of Sciences,2008).

Some creationists dispute this information, claiming that scientists discredit datathat go against evolutionary theory. Nonetheless, there is no room for consideringworldwide, long-lasting conspiracies in science, as scientific fame and recognitioncome from the demolition of old theories, not from adherence to them (Atkins, 1995). Indeed, scientists themselveshave challenged many aspects of the original Darwinian theory of evolution, such asthe importance of neutral evolution, the discovery of epigenetics, the proposal ofpunctuated equilibrium, etc. When these challenges were first proposed, they werenot ignored; they were published in top scientific journals and have been subject tometiculous research and have generated fruitful debates in the scientific arena.

Furthermore, if scientists were dishonestly accepting a false theory of evolution,Lamarck’s theory of inheritance of acquired characters would still be consideredvalid today. However, it is not. In the XIX century, August Weissman (1889) removedthe tails of 20 generations of mice, but no significant decrease in length was foundin the descendants’ tails. Scientists themselves devised the scientific experimentthat bluntly rejected Lamarck’s proposal as a mechanism of evolution (Dobzhansky, 1973). Scientists do not discreditdata that goes against evolution; otherwise, Lamarck’s idea would still be accepted.They discredit scientific untestable theories and explanations that were notgathered using the scientific method.

The cornerstone of biology

Just as human history explains the geopolitical configurations of our world today,modern biological systems are a direct result of their evolutionary past. Hence,evolutionary theory is the cornerstone of the discipline of biology (Rutledge and Warden, 2000). The discipline ofbiology today is an instantaneous portrayal of the dynamic evolutionary axis thatarose with the origin of life and has been changing by evolution ever since (Figure 2). With the first life, genetics,ecology, biochemistry and evolution began.

As a scientific theory, however, which facts does evolutionary theory explain? Onepivotal example is the succession in the fossil record. This evolution, namely,macroevolution, explains the larger evolutionary picture that is the appearance ofthe greater groups, such as the evolution of mammals, insects, and plants.Fossilized mammals are easily recognized, as they have distinct types of teeth, suchas molars, canines, and incisors. These vertebrates are also very likely tofossilize on account of their rigid teeth and hard cranium. If mammals are so easilyfossilized, how can we explain a rich fossil record full of vertebrates andinvertebrates with no mammalian fossil before 300 million years ago?

Similarly, if we dig deeper still, disclosing 500 million years old layers, we findno hard skeleton vertebrates but plenty of fossilized invertebrates in a boost ofdiversity that we call the Cambrian Explosion. There are no vertebrates in thisexplosion because vertebrates appear in a much later explosion. Digging even deeper,to 600 million years old records, we find strata with soft-bodied Ediacaran animalsbut no hard-shelled invertebrates and no vertebrates. In one billion years oldstrata, we find only single-celled organisms.

How can we find, in old strata, many single celled organisms but not a singlemammalian tooth? The only reasonable explanation for these facts is that 400 millionyears ago, mammals had not yet evolved; 500 million years ago, vertebrates had notyet evolved; 600 million years ago, hard-shelled invertebrates had not yet evolved;and one billion years ago, multicellular life had not yet evolved. Smaller localsuccessions are also observable in the fossil record; such as the beautiful stringsof intermediate fossils that include amphibians (Kustchera and Elliot, 2013), birds, whales (Thewissen, 2009), horses, andhumans. These successions in the fossil record are the most obvious evidence tomacroevolution (Figure 2). In fact, the entirefossil record is a set of millions of intermediate fossils that provide solidevidence of how macroevolution worked in the past billion years.

Evolutionary processes that drive micro and macroevolution are facts

To have a better understanding of evolution, we must discuss the processes that driveevolution. For this, we start by comparing processes that drive microevolution withthose that drive macroevolution. Many of the same evolutionary processes that drivemicroevolution also drive macroevolution, namely natural selection, mutation,migration, and genetic drift. A lineage will tend to diversify if it has adaptationsthat increase survival and reproductive abilities compared to other species. Thisadvantage will tend to increase population size and the geographical distribution ofthe ancestral species that will more likely speciate into two descendant species.Hence, according to this view, macroevolution is microevolution on a larger scale(Zimmer, 2001), with biologicalspeciation as the only additional process (Russoet al., 2016). Through speciation, one ancestralspecies gives rise to two descendant species that are reproductively incompatiblewith each other.

More than a million species have been described (Moraet al., 2011), and each biological species includesmany interbreeding members. Also, most species are reproductively isolated from eachother. The fact that we observe biological species with interbreeding members andreproductive isolation between species is compatible with both separate creation andmacroevolution. So, which observable pattern would we expect if many speciationevents generated the vast biological diversity from a single common ancestor? Inthis case, we would expect different degrees of similarity between reproductivelyisolated species. This is exactly what we observe. Some species are very similar,such as chimpanzees and gorillas, with most features shared between them. Otherspecies, on the other hand, are morphologically so different that one must look intocytology, physiology, or comparative genomics to detect evidence of their commonpast. One example is a fern and a frog. For instance, the cellular respiration is aprocess shared by ferns and frogs and it is an evidence of their common ancestry.Only macroevolution explains well the distinct degrees of similarity between thesefour isolated species, as the age of their last common ancestor is inverselyproportional to the similarity between any two species.

Furthermore, the existence of hybrids, such as the mule, the liger, the coywolf, isalso only explained by the hierarchical common ancestry theory, not by separatecreation. The hybrids are direct evidence of on-going processes of speciation. Thus,the presence of hybrids is what we would expect if all life had a commonancestry.

Other fossil record patterns are well explained by macroevolution. For instance, whydo we find a major increase in mammalian fossil diversity only after thedisappearance of non-avian dinosaurs approximately 65 million years ago? The samepattern is observed in the fossil record of birds. Macroevolution explains thiswell, as the extinction of dinosaurs eliminated competition, and the survivingancestral mammals were able to increase in number and diversified throughspeciation, generating more species of their kind.

Final remarks

A single, very well designed experiment, performed in accordance with the utmostscientific standards, is what it takes to put any scientific theory to rest. Divinecreation will never be part of science because science is not able to detectsupernatural phenomena. Divine phenomena explain everything equally; hence, itprovides no real explanatory (i.e., predictive) power. If we accept “God’s will” asan adequate explanation for a natural phenomenon, we eliminate the possibility ofeventually being able to explain it naturally. Thus, the scientific revolution begunwhen we eliminated the divine as a scientific explanation.

Science, as a process, starts with the acceptance of our ignorance about a naturalphenomenon and by seeking natural explanations for it. Hence, ignorance drives theengine of Science. Even if evolution were, hypothetically, rejected, contested bynew data, scientists would have to study hard to find an alternativenatural explanation that was able to explain everything thatevolution explains today plus the new data that contested it.

Evolution is a fact and a well-supported scientific theory. It has endured daily andrigorous testing, and it stands as the unifying theory in biology (Rutledge and Warden, 2000). This says nothingabout whether God created or did not create the world, as science is unable todistinguish a divinely guided evolution from a materialistic evolution. God may wellhave created the biological world through natural selection, mutation, speciation,extinction, etc. Still, evolution and Science would remain unscathed as Science isnot concerned with why or who, but only withhow.

Some creationists say that we must bring the evolution versuscreationist debate to the classroom and claim that the opposition to the debate isanti-scientific. However, science is not about blind criticism (Meyer and El-Hani, 2013). Blind criticism isjust as naïve as blind acceptance. Scientists must weigh the evidence beforequestioning a theory. The idea that all debates are equally scientific is misleadingand it explains the sad emergence of flat-earthers and anti-vaxxers. A debate onwhat is the shape of our planet is not only pointless, but it is also dangerouslyharmful to the minds of the young students. A fruitful debate in a science class isrestricted to those issues that lie within the scientific realm (Baltzley, 2016, Branch, 2016).

A recent study has suggested that science concepts, more than evolutionary basics,are critical to promoting evolution (Dunk etal., 2017). One way to reinforce these fundamentals would bethe requirement of evolution and science fundaments in admission policies forbiology professionals, particularly teachers (Larkinand Perry-Ryder, 2015; see Rutledge andWarden, 2000 for statistics).

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