Darwin at 200, Origin at 150

2009-02-12

2009 marks 200 years since the birth of Charles Darwin, and 150 years since the publication of his best-known work, fully titled “On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life”, retitled in later editions as simply The Origin of Species. Perhaps the best known scientific document ever produced, The Origin of Species literally changed the way we perceive ourselves, to a degree only rivaled by religion. Indeed, while Darwin’s book sold out immediately upon its first publication, having been written for consumption by the general public, its reception was mixed from the beginning by criticisms regarding its conflicts with the Genesis account of creation found in the Holy Bible. Darwin, who had originally been educated in divinity at Cambridge University with the intention of becoming a clergyman with the Church of England, knew all too well the consequences of his work, and the resistance it would face, leaving him reluctant to publish his findings, once remarking “it is like confessing a murder!” Only after he was contacted by Alfred Wallace, who had independently developed essentially the same theory, did Darwin decide to publicize his conclusions.

While the birth of paleontology was beginning to reveal a plethora of extinct species so numerous that a static “one-time” account of creation was beginning to look doubtful by the time Darwin was born (or at least very grim, with the current population accounting for just 0.1% of all species evidenced in our history), until Darwin’s time no one was able to propose a coherent alternative hypothesis. Ideas of the transmutation of species had existed for hundreds of years past, but a process so difficult to observe required a powerful explanation to gain acceptance, an obstacle avoided with past theories like Newton’s law of universal gravitation, which was sufficiently obvious to gain global acceptance without the remotest idea of its mechanisms. It was not common descent from earlier species that Darwin is credited with demonstrating, it is merely the mechanism of random mutation and natural selection. As his contemporary Thomas Huxley (the biologist who coined the term “agnostic” and grandfather of famous novelist and pacifist Aldous Huxley) put it, “How stupid not to have thought of that!”

150 years later, the skew between acknowledgment of evolution by citizens of first world countries (a mere 40% in the United States) and experts in the field of biology (100%, very gently rounded up to the nearest percentage point) is both startling and unprecedented. Only in recent decades have the world’s major religious leaders begun undoing centuries of censorship, with Pope John Paul II being the first to make an official declaration on behalf of the Roman Catholic Church that evolution was “more than a hypothesis”, and the Church of England published an apology to Darwin for their criticisms only four months ago. Especially in the United States, law, politics, and education are still in a fluctuating dynamic, having battled at first on the issue of whether to allow the teaching of evolution at all in government-subsidized institutions (most famously seen in the 1926 Scopes trial, where a teacher was successfully convicted in a Tennessee court of teaching evolution and charged a $100 fine), and today on whether to allow requiring alternatives to be taught alongside it (seen in such cases as the Dover trial of 2005, where it was decided that intelligent design was a religious movement, and as a result could not be taught in Pennsylvania’s Middle District public school science classrooms).

Policies on these topics exist in British Columbia, but have not endured the same legal processes as in the United States. Public schools and Group 1 independent schools (those which receive 50% of the per-student operating grant that public schools receive, of which 71.74% of independent school students in BC attend) are required to employ BC certified teachers and meet BC learning outcomes. The Educational Standards Order clarifies this, stating that while independent schools have the freedom to approach the curriculum from their own perspectives, learning outcomes must be met for all subjects that contribute to a British Columbia Certificate of Graduation, which includes a recommended 5 – 10 hours of class time spent on the topic of evolution in Biology 11, and that “while respecting the personal beliefs of students, teachers should be careful to distinguish between knowledge based on application of scientific methods, and religious teachings and associated beliefs such as creationism, theory of divine creation, or intelligent design theory”.

Unfortunately, despite these advances in the freedom for scientific advancement and understanding, evolution is still poorly understood by the general population. Having spent several months studying, among other things, the theories and history of thought regarding the origin of life, I hope I might be able to help remedy that today. While I find it difficult to quantify my level of knowledge, having never taken so much as a high school biology course, and having gathered more of my information from Wikipedia and YouTube than textbooks and teachers, I am reasonably confident regarding the specific statements I make in this article, and would be happy to supply additional links or answer questions clarifying details beyond that.

Mutation and Natural Selection Darwin’s primary contribution to the theory of evolution was his idea that natural processes cold have a similar effect to the intelligent breeding choices human beings made shepherding their own animals, slowly guiding changes in a species over time, selecting only those suitable for the purpose of survival and reproduction. It was, of course, always known that descendants were not visibly perfect hybrids of their parents, but it was generally assumed that some level of variance within a static species was normal, and that limitations to this were a part of the species itself. Darwin proposed that mutations were not in themselves limited, but that by means of “natural selection”, only those individuals that were capable of surviving to a reproductive age, finding a mate, and rearing offspring of their own were capable of passing on their mutations to future generations. As a result, in situations where a given mutation conveyed a competitive advantage, that trait would become dominant, and the species would eventually contain that trait universally, at least within any interbreeding group.

Darwin then proposed that, by isolating a particular group of a species, it could develop new traits independently of the rest of that species. Given enough time, especially in an environment with different selective pressures than those imposed on the remainder of the species, its changes could accumulate to the point where that species was obviously distinct in appearance, behavior and environmental suitability from, and eventually even sexually incompatible with, the group it originated from. At this stage, it should be considered separate.

By this understanding, a species, which has never been a particularly well-defined term, is essentially any group of animals capable of interbreeding, distinct from other groups. There may be overlap between groups, and there may be change in any given group over time, complicating matters of classification, but there should not be limits to the similarities between a creature and its distant ancestors, barring the physically impossible.

Today, we know that complex living organisms and their traits are determined by a unique combination of DNA, a four-character code operating almost like piano rolls, parsed by the internal machinery of cells to produce appropriate proteins in the necessary sequences. As DNA is duplicated and passed on to our offspring, duplication, deletion, and mutation of genes randomly and indiscriminately occurs, resulting in the variations we see today. While most mutations that are not inert are actively harmful to an individual, living organisms are incredibly resilient to genetic corruption, generally giving offspring a fighting chance at survival. The bodies of conjoined twins cooperate and improvise during their construction. Children with entire additional chromosomes can survive, with effects ranging from Down syndrome to almost none at all in the case of males receiving an extra Y chromosome. Interbreeding dramatically different breeds of animals occurs both frequently and successfully. Evidence shows that entire chromosomes can even be merged together naturally, and successfully, and that this happened somewhere in the development from Homo sapiens after our division from the ancestors that led to the modern chimpanzee. Every individual being contains a unique set of DNA, statistically likely to have not only a new combination of genetic information from their parents, but also previously unseen mutations. While most mutations are impotent or detrimental to an individual, statistical simulations prove that even an overwhelming ratio favoring negative mutations cannot drown out positive ones in the span of time.

Creation of the Tree of Life While the idea of common descent was not completely new in Darwin’s time, his detailed diary and sketches of previously unknown species and distinctly unique breeds of animals did provide significant new insights into the development of the first revisions of a detailed, unified history of descent. On his voyage on the HMS Beagle he catalogued many breeds of finches, tortoises, and other animals that provoked him to begin examining the concept of the transmutation of species over time, reaching the conclusion in his notes that the history of life on earth could be summarized in what he termed a “tree of life”. In his original publishing of The Origin of Species, Darwin outlined his conclusions for how this tree might eventually develop and included a simple hypothetical tree diagram, his only illustration in the book. Today, we know this diagram as the phylogenetic tree, and it has indeed been developed with precise detail over the decades.

The first attempt at a universal tree of life on earth was published in Ernst Haeckel’s 1879 publication of The Evolution of Man, and it has been developing ever since, as additional fossils, living species, and methods of dating and contrasting life have allowed us to extract more accurate details regarding our ancestry.

Key to Darwin and Haeckel’s conclusions was the consistently layered ordering of fossils in the beds he visited, indicating their existence in distinct periods of time according to the geological time scale still under development at the time by geologists like Sir Charles Lyell (and later established in detail by Arthur Holmes). By means of comparative anatomy of developed species and analysis of embryo development (a field in which Haeckel was a pioneer), it became possible to roughly chart the divergence of species from each other on one axis of a graph, against a timeline established through the geological layers on the other axis. While most graphs of even small subsections of life are too complex to produce everything with accuracy and to scale, today a tree of life can contain data regarding when a particularly enduring genetic line emerged from its ancestors, and for how long it endured, rather than simply when it diverged from its cousins, relative to past and future divergences.

Verification of the Tree of Life With the advent of radiometric dating, two great things became possible in the re-enforcement of an evolutionary understanding of the world. First, carbon dating provided a second independent method of determining whether or not fossils were from different time periods after all. As was expected, carbon dating and the geological timescale were in agreement, finding that fossils from more modern animals were consistently newer than those suspected to be long-extinct. Again and again, the orders agreed with each other, showing a single distinct continuum of species development over time. No mammals or birds dated as far bar as the early reptiles, no reptiles as far back as the early amphibians, no amphibians as far back as the early fish.

Second, it became possible to measure with greatly improved accuracy the precise ages of individual fossils, rather than simply ordering them and only loosely estimating their ages like the geological timescale. Individual species could be dated and even identified more easily, and far bolder claims could be made about the precise order of emergence of new forms of creatures.

The next major test of the tree of life, having filled out many of its branches since the advent of radiometric dating, came with the advent of precise genetic sequencing. Genetics provides us with the ultimate look into our past, establishing not just when, but precisely what changed in us with the progression of time. Not only could precise statistical statements be made about the amount of divergence between species, but we could follow these trends back down the tree, and determine where they occurred, allowing us to predict precisely which species would be eligible to inherit those traits in future generations. Once again, this new method of analysis was in perfect agreement with past methods, only adding further clarity and detail to our understanding of life.

Predictions Made by the Tree The collective data leading to our modern understanding of the phylogenetic tree tells us not just how different the species of the modern world are, but when they became that way, branching off from their shared roots. We can extrapolate numerous predictions from these circumstances. First and foremost, we predict that all sufficiently complicated life forms will have a long history of ancestors we can detect, the “missing links” that connect it to the rest of the tree. Fossilization is not especially common, and some mutations, sufficiently pressured by natural selection, can advance relatively quickly, making it difficult to provide a truly smooth continuum of primary sources of evolutionary samples, but we will certainly be able to grind down larger gaps into smaller ones over time, leaving no wildly free-floating species radically different from anything else.

An extension of this prediction is that we can not only say that we will find missing links, but we know that they will resemble a mixture between a given species and its more distant ancestors. We also know that radiological dating will reveal results in between those two species states, and that we should dig to the correct geological layer to find them, in the same physical region shared by the two species states. An excellent recent example of these predictive methods can be found here in Canada, where in 2004 a fish-tetrapod transitional link named Tiktaalik was found, just as predicted. Some may see this as effectively knowing the mind of God!

We can also use our most modern trees, produced with genetic precision, to make very precise statistical statements regarding individual characters of DNA throughout the tree. Consider for a moment, a hypothetical situation involving three modern day species, A, B, and C, which have been found to have the following percentages of genetic similarity:

Without our theory of common descent, it would be impossible to accurately predict whether or not specific genes would be present in a given species, given the details of any of the other two. For example, if A and B both have a trait, will C have it as well? If A has it but B doesn’t, can we assume that C does not as well? We could not say.

Now, consider instead of percentages of similarity, a tree showing the order in which these species diverged from common ancestors.

Remember that the vertical axis represents time. Although it is not to scale, we can now safely say that any trait shared by both A and B must have been generated before the A line split from the BC line, and must be common to C as well. We can also say that a trait in A but not B must have occurred after the split, and will not be in C. We also know that a trait common to B and C does not necessarily also belong to A. These predictions are not only testable, but have been used in practice, tens of thousands of times. Of course, all genetic traits are susceptible to mutation over time, but our predictions can precisely incorporate the potential for random mutations (which occur at a known, established rate). In fact, not only can we predict the odds that a trait will disappear (or independently reappear, a very unlikely but possible occurrence), but in the case of inert DNA material that does not manifest itself in any way to impact the survivability of the species, thereby eliminating pressures from natural selection, we can predict precisely how mutated on average the variants of each trait will be from each other! In other words, we know not only where specific sequences of DNA will be, but how closely they will resemble their cousins!

In the near future, I hope to follow up this note and cover common misunderstandings and questions regarding evolution, such as the generation of complex sensory organs like eyes and ears, and life-critical systems like lungs and skeletal-muscular systems. I’ll also touch on the origin of sexuality, consciousness, aging, generosity and self-sacrifice, and address common questions like “why don’t we see half-reptile/half-bird hybrids” and “why do we still have apes?” Not all of my statements can be completely certain, but those that aren’t are respectable hypothesis, many of which are gaining more and more supporting evidence all the time.

You can find books like The Origin of Species at bookstores all around town, and modern books on the topic like The Selfish Gene are available at the local library and of course can be ordered online.