Across the next 10 articles, I present a few of the quirky examples of evolution that we can readily observe in nature. It is by no means an exhaustive list, but merely a set of stories which I feel illustrate well the power of evolution to create complexity, and how we can see evidence for natural selection by looking carefully at the idiosyncrasies it has produced.
The examples I provided in this series can be broadly categorised into a few themes; coevolution (Fig Wasps and Hawk Moths), evolutionary constraints on adaptation (Pandas, The Human Eye), convergent evolution (Birds and Bats), adaptive radiation (Galapagos Finches, Ring Species) and homology (DNA and the Pentadactyl Limb). And within each of these categories, there are numerous other stories I could have told to illustrate my point. But the point I am trying to illustrate is that evolution is a real phenomenon. Charles Darwin’s theory of evolution by natural selection is one which explains the natural world around us in both a satisfying and verifiable way.
Science is based upon the testing of hypotheses. The philosopher Karl Popper concluded that an idea or hypothesis can only be considered scientific if it is falsifiable; that is, it is possible to prove it wrong. For instance, the statement “all sheep are white” is falsifiable – you would only have to find a single black sheep to prove that hypothesis wrong. Likewise, the theory of evolution absolutely is falsifiable. A find of a single vertebrate fossil in pre-cambrian rocks would immediately falsify the theory. That this fossil has never been found, is only part of my point. Science can only progress by the testing of falsifiable hypotheses – an idea which cannot be proved wrong is not a scientific one, it is an issue of faith. Science can never really claim to prove a falsifiable hypotheses to be correct however, we could sample a million sheep but we still could not be certain that there wasn’t a black one out there somewhere. But the more we test a hypothesis, if we are still unable to prove it wrong, we become increasingly sure that it is an accurate representation of the world. This is how science progresses, an initial hypothesis about how the world might work, if robust to repeated testing, over time becomes a strong theory, and eventually becomes something we can comfortably agree to be fact.
Evolution is not just falsifiable, it has also been supported, time and time again, by every piece of empirical research conducted. Laboratory populations, subjected to artificial selection, evolve both morphologically and genetically over time, and their improvements in fitness can be quantified. Wild populations, when subject to rapid climatic change, adapt in observable and measurable ways. Wherever we look, we see homologies between species which in all other ways appear to be distantly related; DNA, the five-fingered foot (or hand!), skeletal structure, developmental (HOX) genes, protein conformation…. And we see convergence upon similar solutions to similar problems between species.
Criticisms of the theory generally stem from a few key, and erroneous, assumptions:
- Life is too complex to have evolved. Even at the smallest level, components of life are so complex, that if they were even slightly different they would not function at all. Therefore life cannot have evolved gradually through small changes.There is no example of any organ, cell type or adaptation of any kind whose origin cannot be explained through a series of gradual changes, each of which produced an individual better suited to it’s environment than the last. Evolutionary biologists have postulated realistic scenarios for the origin of life itself and many examples of apparently ‘unevolvable complexity’ such as the eye. In many cases, examples of living creatures with intermediate forms of these traits are available, as is the case for the evolution of sight.
- Evolution can shape changes within species, but cannot create new species. Nobody has ever witnessed, or provided an explanation for, the origin of new species. This highlights the distinction between micro and macro-evolution. We have ample evidence for micro (short-term) evolution, both from domestication and artificial selection experiments. Macro (long-term) evolution is far more difficult to demonstrate because it, by definition, tends to take longer than a single human lifespan to occur. However, there is a great deal of evidence consistent with the creation of new species through the same evolutionary processes that we can observe in the short-term. Transitional fossils in the fossil record are strongly indicative of a gradual transition from one species to another. Ring species show how small changes between geographically separate populations can gradually accumulate leading to reproductive incompatibilities (and thus speciation) at the extremes. Additionally, there are numerous examples of quite rapid evolutionary change in species exposed to new environments, such as the Galapagos finches that helped to inspire Darwin, as well as invasive and introduced species across the world. Although some evolutionary biologists have postulated a more stop-start mode of evolution, known as punctuated equilibrium, this still has no requirement for a deity or creator, and continues to operate on the basic mechanisms upon which natural selection is based.
- The Second Law of Thermodynamics states that energy within a closed systems is subject to entropy, meaning these systems will tend towards increasing disorder. Thus evolutionary theory defies this basic concept of physics and cannot possibly account for the diversity of ordered systems of life alive today. The second law applies only to closed systems, for which energy can neither enter nor leave the system. The Earth is not a closed system – energy is continually input into the system by the sun. Furthermore, the theory of entropy allows for localised pockets of order within a system, as long as overall across the system disorder is increasing. Thus the second law is not an issue for the theory of evolution.
- There are no transitional fossils demonstrating individuals intermediate between two species, which is predicted by the theory of evolution. This is absolutely not the case. There are numerous transitional fossils for just about every transition that you can think of – the move from water to land, the evolution of flight and even human evolution. Where transitional fossils are lacking, there are many good explanations for this; fossilisation is an extraordinarily rare occurrence which is biased towards certain types of species (in particular, soft-bodied creatures are usually left out), living in certain environments, even when fossilisation does occur, fossils can be destroyed by tectonic movement, erosion or numerous other destructive processes, and even those that survive have not all been found yet. In fact, the numerousness of transitional fossils is pretty remarkable given all of these constraints, and is support for the theory in itself!
- If humans evolved from monkeys, then why are there still monkeys? First of all, please refer to my rant on the distinction between monkeys and chimpanzees before reading any further. This criticism arises from a basic misunderstanding of evolution and the relationships between extant species. Humans are most closely related to Chimpanzees, and more distantly (but still pretty closely) to monkeys, and other primates. Technically speaking we did not evolve from Chimpanzees. More correctly, we share a common ancestor with them. Sometime in the past (around 7 million years ago), there was a species of ape in Africa that split into two populations which, over time, diverged into different species. Both human and chimpanzees superseded their common ancestor, but neither species evolved from the other. Chimpanzees are not simply unevolved humans – they are as recent a species as we are, and they have been evolving and adapting to their environment for as long as we have. The evolution of life is best imagined as a family tree, with one species giving rise to daughter species which either survive or die out. No species truly replaces another, in evolutionary terms (although sometimes the do ecologically if they are able to outcompete).
- Finally, the rather childish “it’s only a theory” rebuttal, which is evidently lacking in substance, can be explained by the erroneous interpretation of the word ‘theory’. I have recently been reading Richard Dawkin’s excellent book “The Greatest Show on Earth” and upon reading the section refuting the “its only a theory” argument, I realised that not only was he saying exactly what I had wanted to say here, but had done so far more succinctly and passionately that I could ever hope to imitate. So, instead, I shall simply refer you to his words:
- Theory, Sense 1: A scheme or system of ideas or statements held as an explanation or account of a group of facts or phenomena; a hypothesis that has been confirmed or established by observation or experiment[…]
- Theory, Sense 2: A hypothesis proposed as an explanation, hence, a mere hypothesis, speculation, conjecture[…]
Obviously the two meanings are quite different from one another. And the short answer to my question and the theory of evolution is that scientists are using Sense 1, while the creationists are – perhaps mischievously, perhaps sincerely – opting for Sense 2. […] Evolution fits Sense 1 perfectly. Darwin’s theory of evolution is indeed a ‘scheme or system of ideas or statements’. It does account for a massive ‘group of facts or phenomena’. […] The more energetically and thoroughly you try to disprove a theory, if it survives assault, the more closely it approaches what common sense happily calls a fact” Dawkins (2009)
Evolution is fact. Or as close to fact as we can ever hope to get. Just as gravity, the spherical shape of the Earth, the behaviour of particles and waves are fact, evolution is a fact. And to the final criticism, that evolution strips away the wonder and splendor of nature, by explaining it in mechanistic terms, in my opinion, viewing life from the perspective of Evolution makes it all the more beautiful. It makes all of life’s intricacies and idiosyncrasies more interesting, more splendid, more wonderful.
“There is grandeur in this view of life … from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved.” Darwin (1859)
Articles in this Series:
- Intro: Reasons Why Evolution is True
- Part One: The Panda’s Thumb
- Part Two: Parasitoid Wasps
- Part Three: Ring Species
- Part Four: Galapagos Finches
- Part Five: The Quirky Human Eye
- Part Six: Homology
- Part Seven: Coevolution
- Part Eight: PreCambrian Rabbits
- Part Nine: DIY Evolution
- Part Ten: Convergent Evolution
Featured image is used under a creative commons licence from Wikimedia commons. Original image by Laitche