Charles Darwin in his later years. The year 2009 marks his 200th birthday.
Source: Wikimedia Commons. Photo by J. Cameron, 1869. Original source: Harvard University publications.
Charles Darwin (1809-1882) was an extraordinary man by any standard. The theory of evolution by natural selection as elaborated in his book, On the Origin of Species,1 is considered by historians and philosophers of science to be one of the most important ideas that the human mind has ever produced.2 The implications of his very useful insight extended beyond science and profoundly impacted the human mind.
Darwin’s big ideas
Darwin was born and educated at a time when special creation was the prevailing scientific view. That is, God created the universe and all species a few thousand years ago, and they were unchangeable. “Revelation”—not research—provided this view. Darwin began the HMS Beagle voyage (1831-1836) with this belief. Observations made during the voyage—a surveying trip around the world, which included a stop in the Galapagos Islands—made Darwin question the creation myth and immutability of species. He found marine fossils thousands of feet above sea level, and he reasoned that the land had been elevated by earth movements; it had not been inundated in a great biblical flood. Other observations that influenced his thought included:
The fossil mammals he uncovered in South America resembled living mammals from the same area. Why should this be if each species were specially created? Extinction was hardly recognized in those days.
Why did the animals on islands off continental areas resemble those of the nearest land mass if each species were created in place?
Why were there so many species in an island group that looked very similar but with slight differences from island to island? It is as if “one species had been taken and modified for different ends,” he wrote in Voyage of the Beagle.3
None of these things made sense from a creationist perspective. In 1844, he wrote to his botanist friend, Joseph Dalton Hooker (1817-1911) “I am almost convinced (quite contrary to the opinion I started with) that species are not (it is like confessing a murder) immutable.”
The elegant simplicity of Darwin’s reasoning can be distilled as follows:
- There is variation in nature—many more offspring are generated than can survive; therefore, there is a struggle for life in which favorable variations are preserved and unfavorable variations are removed. This leads to evolution, which he defined as “descent with modification” and to the formation of new species.
Nature is doing the selecting for the forms best adapted to a particular environment, so he called the process natural selection—as opposed to artificial selection that breeders impose. We now know that mutation, chromosomal rearrangements, sexual reproduction, and so on, are the sources of genetic variation, but Darwin had no knowledge of such topics. Today we can speak of “descent with modification” as “a change in gene frequency,” and natural selection is simply “differential reproduction,” that is, one genetic variant leaves more offspring than another.4
Darwin borrowed the expression “survival of the fittest” from economist Herbert Spencer (1820-1903). Evolutionary fitness means reproductive fitness. In modern terms, the fittest is the one who gets the most genes into the next generation—not necessarily the biggest or strongest individual.
Darwin’s explanation of evolution via natural selection is the basis of all of biology and its applied sub-disciplines of medicine, agriculture, and biotechnology. No other biologist in the history of our species has had an impact of this magnitude. In the words of the eminent geneticist Theodosius Dobzhansky, “Nothing in biology makes sense except in the light of evolution.”5 The paradigm shift from creation to evolution has moved intellectual endeavors from an untestable beliefs to a rational understanding that flows from the scientific method. This, in turn, has allowed a vast array of advances in knowledge.
One of the attributes of a powerful scientific theory is that it enables future research and understanding. For example:
Darwinian or evolutionary medicine6 explains how some disease symptoms, such as fever, may be a response favored by natural selection as a defense against pathogens. Some genetic diseases such as sickle cell anemia may allow differential survival of its victims in malarial zones—a phenomenon called a balanced polymorphism (genetic variation, e.g., blood types).4 This results in a deleterious gene (sickle cell) being maintained at a relatively high frequency in a population, even though it can be lethal in a double dose (homozygous), because it protects its carriers against malaria when present in a single dose (heterozygous).
Evolutionary thinking explains the arms race waged by pathogens and hosts that prevents either from being eliminated completely. Darwinian reasoning easily explains the development of antibiotic-resistant bacteria through the flagrant overuse of antibiotics. A drug kills the susceptible bacteria leaving bacteria with a pre-existing resistant mutation to build up the next generation. Then when you actually need the antibiotic for a bacterial infection, patients and doctors find that the drug is ineffective. This is evolution, pure and simple.
- A similar process occurs in agriculture with the overapplication of pesticides, and the formation of pesticide resistant pathogens, insects, and noxious plants. Australians are very familiar with the myxomatosis versus rabbit “arms race,” whereby the virus initially killed 99% of the non-native rabbits. The virus that causes myxomatosis was introduced deliberately in Australia in 1950, in an attempt to control exotic rabbit infestation. Given enough time, however, the surviving rabbits returned in force as the virus evolved in the direction of less virulence, and the rabbits were selected for more resistance to the virus.7
Evolutionary psychology and evolutionary ethics help explain the origin of morality.8,9 Peacemaking among non-human primates by the calming effect of mutual grooming to diffuse aggression may be seen as the precursor of what became morality in humans.10 Modern religions are recent human inventions—a mere few thousand years old. The antecedents of morality, on the other hand, clearly evolved before humanity, as reflected in the empathy exhibited by bonobos (Pan paniscus), and the reciprocity of chimpanzees (P. troglodytes).11 Kin selection, whereby an individual sacrifices for a close genetic relative, makes sense in an evolutionary context because some of the same genes of the individual making the sacrifice will be passed on by the kin who survives. This is referred to as inclusive fitness.12
The ancestry of the AIDS virus, HIV-1 (human immunodeficiency virus-1) has been traced to SIVcpz (simian immunodeficiency virus) carried by our closest living relative, the chimpanzees.13 This is not surprising from an evolutionary perspective. Somewhere in a high school today, there is a student whose future career may contribute to the control of the AIDS epidemic. What chance of that would there be if creationism were taught as science in high school?
- Biotechnology—whether in the form of genetically modified crops, designer drugs, gene therapy, or the human genome project—all derive from Darwin’s profound insight. Darwin had no knowledge of genes or chromosomes, or of how inheritance worked. This required additional input from the understanding of Gregor Mendel’s (1822-1884) genetic work.
The modern evolutionary synthesis grew from Darwin’s explanation of natural selection and Mendel’s demonstration of inheritance augmented by the research of mathematically oriented population geneticists. This fusion of knowledge moved evolutionary science forward to the middle of the 20th century.14 James D. Watson’s and Francis Crick’s 1953 demonstration that the molecular structure of DNA allowed for genetic coding was a huge breakthrough that ultimately made it possible to sequence the three billion chemical base pairs that compose the human genome and identify the approximately 20,000-25,000 genes in human DNA.15,16
Recent discoveries in evolutionary developmental biology, known as evo-devo, have shown that very similar genes are present in very dissimilar animals. These body-shaping genes are controlled by DNA switches called enhancers that turn them on or off at various times in development. Such enhancers are a major factor in the evolution of anatomy.17
- TV viewers are familiar with DNA [deoxyribonucleic acid] analysis popularized on CSI [Crime Scene Investigation] programs. DNA-sequencing techniques—whereby the arrangement of A-T-C-G of genetic codes are compared—can convict or exonerate people accused of crimes. Similar techniques can confirm or deny paternity in disputed cases, or can ensure that the expensive grouper fillets you purchase are not flesh from lesser species. Such evolutionary tests are accepted by the judicial system because they pass the Daubert standard for scientific evidence; that is, the techniques were subject to empirical testing, published in peer-reviewed journals, and accepted by the scientific community.18 No such creationist tests exist; if they did, they could not meet scientific or judicial standards.
The Paradigm Shift
The above examples are just a sample of the benefits to society that flow directly from the creative power of Charles Darwin’s theory of evolution by means of natural selection (for more about Darwin’s legacy, refer to Charles Darwin: The concise story of an extraordinary man19). The publication of On the Origin of Species, on 24 November 1859, precipitated one of those rare events in the history of science—a paradigm shift. Philosopher Thomas Kuhn used this term to refer to the replacement of one world view by another.20 Examples of a paradigm shift in science include the replacement of the earth-centered Ptolemaic system by the sun-centered Copernican system; and the replacement of Newtonian physics by relativity and quantum physics. The paradigm shift instigated by Darwin’s legacy has made obvious the superiority of this scientific method as a means of understanding the world around us.
© Acknowledgment: Adapted from the article “Charles Darwin’s paradigm shift” by Tim M. Berra, published in The Beagle, Records of the Museums and Art Galleries of the Northern Territory, 2008, 24: 1-5. © 2009, American Institute of Biological Sciences. Educators have permission to reprint articles for classroom use; other users, please contact 바카라 가입머니editor@actionbioscience.org for reprint permission. See 바카라 가입머니reprint policy.