Bacteria are becoming increasingly resistant to antibiotics; some butterflies and fish are developing new colours for better camouflage; and a series of laboratory experiments have revealed small but significant changes in various microorganisms. Are these phenomena conclusive evidence of evolution unfolding before our eyes?
The previous article explored some of the issues that the natural selection model encounters relating to the spread of random mutations in a population. We pointed out that natural selection is indeed a force that manifests itself in nature, but the limits of its ability to drive evolution over long periods of time, even millions of years, are debatable. In evolutionary thinking, however, these limits do not exist, as natural selection has the ability to transform a primordial cell into an entire planetary ecosystem, provided it is given enough time. But can testable evidence be provided in this regard? Has naturalistic evolution ever been observed in an experiment? From an evolutionary perspective, the answer is yes: evolution has been observed in numerous studies of natural ecosystems and controlled experiments. These observations supposedly confirm the accumulation of new functional information through random mutations subject to selective pressure.[1] Below, we review the main types of evidence supporting evolution provided by microevolution.
Microevolution
Put simply, microevolution is the spontaneous change of a species occurring in small steps over relatively short periods of time without splitting into several distinct species. The process by which a species diverges into two distinct species is called “speciation” and occurs when a subpopulation becomes reproductively isolated from the main population for a prolonged period, for instance due to a mountain range forming and separating them. Thus, microevolution accumulates different random mutations independently in the genomes of the two groups until the genetic differences between them are large enough for the two groups to be considered distinct species.
A little more rigorously, but also more revealingly, microevolution is defined simply as a variation in the frequency of gene types in a population, provided it does not produce speciation. A gene usually has several distinct forms spread throughout a population, and these distinct forms of the gene are called “alleles”. For example, if a gene is present in a population[2] in variants (or alleles) A and B with frequencies of 20% and 80% respectively, and these frequencies are measured at 30% and 70% respectively over several generations, then this frequency fluctuation is seen as microevolution. It is easy to see how this definition almost guarantees the permanence of a species’ microevolutionary process, since the frequency of alleles in a population is very likely to differ from one generation to the next.
But what does a variation in the frequency of pre-existing alleles in a population have to do with the incremental accumulation of new information in the form of random mutations? This definition “hides” the difficult problem of generating new functional information from random mutations in a rigorously formal but essentially ineffective language, which is revealing of the evolutionary way of thinking. When a new mutation appears in a gene, it is considered to produce only one allele of that gene. This allele previously had a null frequency, meaning it was completely absent from the population. Now, it has a non-null frequency; it is initially present in the individual in whom the mutation appeared and can subsequently spread through the population over generations. In the example above, if we call this allele “C”, it is as if we are measuring the change in the frequency of alleles A, B, and C over several generations, from 30%, 70%, and 0% to 30%, 69%, and 1%, for example. Thus, we see that the definition of microevolution is ingeniously constructed to support the theory of evolution from the outset: on the one hand, the definition refers to a real, verifiable phenomenon in that the frequencies of alleles in a population fluctuate from one generation to the next. On the other hand, the definition implicitly and forcibly equates this process with the addition of new functional information in small steps as required by evolutionary theory.
Macroevolution
From an evolutionary point of view, microevolution is closely related to the complementary concept of macroevolution. Macroevolution refers to long-term evolutionary processes, such as speciation (the formation of new species, facilitated by environmental factors leading to reproductive isolation within a population) and the development of new (or significantly modified) biological structures, and functions. In short, macroevolution is generally considered to be the result of microevolution acting over long periods of time. However, the fossil record[3] and genetic similarities between species[4] provide much evidence contradicting the idea of slow and gradual macroevolution. For this reason, some have formulated the theory that macroevolution is not simply a long-term extrapolation of microevolution, but that it can also occur rapidly in large leaps, although the mechanism is unclear.[5] In general, however, the theory of evolution considers microevolution and macroevolution to be the same phenomenon viewed from different temporal perspectives.
While this has not always been the case, microevolution is now widely accepted, even among those who believe in an intelligent creator of life. However, they consider it to be an intrinsic variability of species within certain insurmountable limits. Opinions are divided as to what these limits are, and which factors limit microevolution. However, the creationist consensus is that macroevolution is not a real phenomenon, and does not necessarily follow from microevolution. In the absence of systematic and convincing arguments to justify these limits of macroevolution, evolutionists ask: if a process can produce evolution on a “micro” scale, why could it not produce evolution on a “macro” scale if given enough time? If someone uses the process of “walking” to move from the bedroom to the kitchen, why can’t they use the same process over a much longer period of time to get from Boston to Los Angeles? This is a valid argument that deserves an adequate response.
Examples of microevolution
Microevolution is a fairly well-documented phenomenon. Examples range from the famous case of the different types of finches observed by Darwin on the Galapagos Islands, to the dreaded MRSA (Methicillin-resistant Staphylococcus aureus) bacterium, which today threatens an increasing number of hospital patients due to its resistance to almost all known antibiotics. In one of his books[6], Richard Dawkins, perhaps the most prominent proponent of evolutionary theory today, presents several cases of microevolution that are truly representative of the theory of evolution.
Elephants in Uganda. Over 32 years of periodic measurements of the elephant population in Uganda’s nature reserves, the average length of ivory tusks was observed to decrease steadily each year. In a normal scenario of natural selection, elephants with larger tusks would have a selective advantage over those with smaller ones. However, the human factor of elephant hunters seeking ivory has intervened, so animals with larger tusks are hunted more than those with smaller tusks, giving the latter a selective advantage. While it is tempting to attribute these changes to microevolution and human selective pressure, there is a problem. In general, evolutionary changes are easier to observe in species with a shorter average lifespan, as more generations can be observed within the limited duration of the experiment. Compared to bacteria, whose average lifespan is usually measured in hours, elephants have an enormous average lifespan of 45 years. Therefore, while we might expect to observe microevolutionary changes in a population of bacteria that goes through tens of thousands of generations in three decades, for elephants, three decades represents only a few generations. For this reason, Dawkins hesitates to make a definitive statement, speculating only that the loss of tusks in Ugandan elephants may be an example of “ultrafast” microevolution. But isn’t that way too fast for natural evolution?
Lizards in Croatia. In 1971, a species of insectivorous lizard called Podarcis sicula was found on the Croatian island of Pod Kopiste but not on the neighbouring island of Pod Mrcaru. That same year, several researchers transported five pairs of Podarcis sicula from Pod Kopiste to Pod Mrcaru, leaving them there. In 2008, 37 years later, another group of researchers arrived on Pod Mrcaru to study the outcome. They found a thriving population of Podarcis sicula, but with notable differences from the original population on Pod Kopiste. The lizards had changed from being predominantly insectivorous to being predominantly vegetarian on the new island. This dietary shift appeared to trigger other changes: the lizards’ heads were larger with more developed muscles capable of producing a stronger bite. Upon dissection, the digestive system also appeared to have changed: the cecum, which is attached to the intestinal tube, contained cecal valves. These are morphological structures commonly found in specialised herbivorous animals, and make the cecum more efficient[7]. And all of these changes occurred within just 37 years—equivalent to only 18–19 generations of lizards, given their average lifespan of two years. Dawkins is enthusiastic about the astonishing speed with which these scientifically documented changes occurred and considers them to be an unambiguous example of “evolution before our very eyes”.
Guppies are a species of tropical fish that are very popular with aquarium enthusiasts around the world for one simple reason: the males are brightly coloured with large, extravagant tails. While this makes it difficult for them to escape or hide from other predatory fish, these characteristics are apparently highly valued by female guppies. The selective pressure on male guppies therefore comes from two opposing forces: females’ preference for the most vivid colouring, and the need to blend in with the environment to avoid predators. Ethologist and evolutionary biologist John Endler observed the changes exhibited by guppy fish in both their natural environment (streams) and in simulated natural conditions (temperature-controlled ponds in greenhouses). Dawkins summarises the results of Endler’s experiments, conducted over several years, noting that, in the absence of predators, male guppies tend to become more extravagantly coloured due to selective pressure from females. However, when predators are present, the colouration of males tends to resemble the type of gravel at the bottom of the water over generations, achieving formidable camouflage. As these adaptive changes occurred in fish populations over a very short period of time, from a few months to a few years, Dawkins once again concludes that evolution is happening right before our eyes.
Adaptive laboratory evolution
The average lifespan of guppy fish and Podarcis sicula lizards is two years, whereas elephants live for 45 years on average. Given the evolutionary changes that can be observed in these animals over years and decades, imagine what we could observe in bacteria, which have an average lifespan of only a few hours, says Dawkins in his introduction to his main example of observed microevolution: the long-term evolution experiment conducted by bacteriologist Richard Lenski at Michigan State University in the USA.
The experiment begins with a culture of E. coli bacteria, with which Lenski “infects” 12 different environments containing the same combination of nutrients, including glucose. Demonstrating true perseverance and meticulousness, Lenski’s team has performed the following daily ritual uninterrupted since 1988 (the experiment is still ongoing): at the end of each day, a sample of bacteria is taken from each of the 12 cultures and placed in a fresh nutrient medium identical to the previous ones. The remaining bacteria are discarded, but not before another sample is separated for freezing and storage. Over time, these samples form a kind of “fossil record” of the experiment’s evolution. The main nutrient that E. coli can metabolise from this medium is glucose, which is dosed in insufficient quantities to last until the middle of the next day. Consequently, each line of bacteria undergoes a daily cycle of prosperity and starvation, which, in the long term, creates ideal conditions for evolution through natural selection. Since the beginning of the experiment, over 80,000 generations of bacteria have passed. What are the results?
Firstly, as expected, each of the 12 bacterial lines has become increasingly efficient at metabolising glucose over time, which was to be expected. Interestingly, the bacteria in all 12 cultures “decided” that increasing their volume was the way to become more efficient. While the 12 cultures did not increase the average size of a bacterium at the same rate, the trend for each was consistently positive, and they eventually plateaued at different levels. More interestingly, two of the cultures followed exactly the same trend in size increase. Therefore, it is highly likely that these two lines experienced the same changes in the same order, independently of each other. On closer inspection, it was found that the same 59 genes changed their expression levels in both lines of bacteria. Furthermore, the way in which the expression level of each of the 59 genes changed—either decreasing or increasing—was identical in the two lines of bacteria. Dawkins considers the likelihood of such perfect microevolutionary parallelism occurring “by chance” to be inconceivable. He concludes that, since it happened “before our very eyes,” despite all odds, it could not have happened by chance as creationists would argue. Rather, we are dealing with an impressive example of the “power” of natural selection in evolution. We will analyse this interpretation later.
However, this is not the most interesting aspect of the experiment. After around 33,000 generations, one of the 12 cultures began exhibiting extraordinary behaviour: the maximum density of bacteria in this line was six times higher than normal every day. It was as if the bacteria in this line were receiving much more food than the others. Of course, this was not the case. The nutrient medium contained glucose and large amounts of citrate, a substance that E. coli bacteria cannot metabolise in the presence of oxygen. This was the same situation as when Lenski began the experiment. However, it was discovered that this strain of E. coli had acquired the ability to metabolise the citrate in the nutrient composition, thus giving it access to a much larger amount of food. Detailed investigations by one of Lenski’s students of frozen bacterial samples from the experiment’s “fossil record” revealed an even more surprising fact[8]. The ability to metabolise citrate did not emerge in a single mutational step, but rather through a preparatory step that occurred after approximately 20,000 generations.
In summary, the mutations necessary for citrate metabolism occurred in two stages, A and B, at around generations 20,000 and 33,000 respectively. Dawkins emphasises that this result is a supreme example of the acquisition of a new function through microevolution observed in the laboratory without hiding his satisfaction that it also invalidates the “irreducible complexity” arguments put forward by creationists. The theory of irreducible complexity argues that a complex biological function cannot evolve gradually because it can only manifest itself after a series of subsystems become available simultaneously, with each subsystem having no biological function when taken separately. Yet in Lenski’s experiment, as Dawkins rejoices, we see exactly that: the emergence of a new function (citrate metabolism) from two “subsystems” of mutations, A and B, each of which has no individual selective value. Nevertheless, we must analyse whether the argument of irreducible complexity is truly invalidated by this experiment or if it points to other interpretations.
Evolution through the eyes of the observer
So far, we have outlined what is meant by microevolution and provided some examples chosen by one of the most prominent evolutionists of our time. We have described the main types of evidence for evolution provided by experiments and direct observations without yet refuting them or presenting a creationist perspective.
Many questions remain: Does this evidence definitively demonstrate how “new” and biologically functional information can be incorporated into the genome through microevolutionary processes involving random genetic changes? Is macroevolution an inevitable result of microevolution over time? If not, what are the limits of microevolution, and how can we test these experimentally? Can the pro-evolution evidence be interpreted from the perspective of an intelligently designed mechanism with certain capacities for variability in order to occupy diverse ecological niches? Is this type of creationist argumentation unfounded, or is it at least as well-founded as the evolutionary perspective? How can we distinguish between the two models? We will explore these questions in a future article.
