IDEAS / Bill Meacham : How Evolution Works

Charles Darwin: Blame it all on him. Image from Wikimedia Commons.
Evolution

Regardless of your opinion on the ultimate purpose of it all, it is important to understand how evolution works because the theory reflects reality, and basing your actions on reality works out much better than not.

By Bill Meacham / The Rag Blog / May 20, 2012

If we want to know what human nature is -- and we do, as that will tell us how to live a fulfilling and happy life -- then we have to understand evolution.

The theory of evolution describes how generations of living organisms change over time. Humans are living organisms. We are subject to and products of the same evolutionary pressures as all other living things. Understanding how we got to be as we are gives us insight into how we function. Knowing that, we can adjust our actions so as to function well.

It is called the theory of evolution, but “theory” does not mean conjecture, speculation, or mere opinion. The term in its scientific sense means a well-supported body of interconnected statements that explains observations and can be used to make testable predictions.

The theory of evolution has been confirmed over and over again.(1) No serious biologist takes it as anything but fully established. In the words of Theodosius Dobzhansky, author of a major work on evolution and genetics, “Nothing in biology makes sense except in the light of evolution... Seen in the light of evolution, biology is... the most satisfying and inspiring science. Without that light it becomes a pile of sundry facts, some of them interesting or curious but making no meaningful picture as a whole.”(2)

It is unfortunate that religious fundamentalists, misusing the term “theory,” regard evolution as unproven. Some go so far as to say that all the evidence that leads us to believe in the immense age of the universe and the proliferation of species over time, as opposed to instantaneous creation some 6,000 years ago, were planted by the creator merely to give the appearance of great antiquity.

Dobzhansky, a Christian, has this retort: “It is easy to see the fatal flaw in all such notions. They are blasphemies, accusing God of absurd deceitfulness. This is as revolting as it is uncalled for.”(3)

The religious believer may view evolution as God’s way of creating the world. The pantheist mystic may view evolution as the One Being’s way of unfolding and coming to know Itself over time. The secularist, the atheist or the merely agnostic may view evolution as the way living beings have propagated themselves, blindly and without foresight, in increasing diversity and complexity.

Regardless of your opinion on the ultimate purpose of it all, it is important to understand how evolution works because the theory reflects reality, and basing your actions on reality works out much better than not. So the rest of this essay is a summary of the theory of evolution.


The term “evolution” in a general sense means a process of change or growth, often taken as a process of continual change from a simpler to a more complex state. In biology, the term refers to two things:

• The observed fact that the distribution of inherited traits in a population of organisms can change from generation to generation.
• The theory that the various types of animals and plants we find around us, including ourselves, originated in earlier types and that their differences are due to modifications in successive generations.

The basic concept of biological evolution as we understand it today is surprisingly simple. Charles Darwin, its originator, called it “descent with modification.” The concept is this:

• An organism’s offspring may vary slightly from the organism itself. Offspring may have slightly different traits from the parents or the same traits in different degrees.
• Organisms typically produce more offspring than can survive and reproduce, given the resources available such as food, shelter, sexual mates, etc. Hence, there is competition for such resources.
• In the competition for resources, some variations have an advantage over others. For example, one child’s beak may be slightly better at picking up small seeds than another’s, or one child may have slightly better eyesight than the other and hence be better able to find food and avoid predators.
• The individuals with advantageous variations have more offspring than those without.
• Since traits are heritable (are inherited from parent to child), this causes the population, over time, to contain more of the favorable variations and fewer of the unfavorable ones.

Darwin called this process “natural selection,” as opposed to artificial selection, the intentional breeding for certain traits that produces such differences in the same species as the Great Dane and the Chihuahua. The underlying mechanism is the same in both kinds of selection: certain individuals have more offspring than others, so their traits become more widespread in the population of that type of organism.

A subset of natural selection called “sexual selection” is a result of competition for mates. In order to have offspring, an individual must not only survive but reproduce. Competition for mates, most often among males for females, selects for traits that enable males to dominate other males, such as horns and antlers, and for traits that attract females, such as plumage and other adornments.

This process happens slowly but inexorably. The variation between parent and offspring is most often minuscule, but over enough generations large changes result. A series of small, incremental changes can, given enough time, produce the extraordinary variety of speciation we find around us.(4)

This process is not purposive.(5) No organism intends to produce a better beak or a better eye. It is merely a fact of life that those with favorable variations tend to have more offspring than those without, each of which in turn have the favorable variation. Among that generation’s offspring, those that further amplify the favorable variation have more offspring, and so on for generations. Conversely, unfavorable variations tend to die out over time. We should not take phrases such as “designed by natural selection” as implying a conscious, deliberate designer.

What is inherited is a trait, a feature of an organism such as eye color. Traits are passed from generation to generation as discrete units. Gregor Mendel conducted a famous study in which he mated pea plants, some of which had purple blossoms and some of which had white. The offspring did not have pale purple blossoms, but rather some had purple and some white, in distinct proportions.

What passes these discrete traits from generation to generation is the gene, the fundamental physical and functional unit of heredity. A gene is a segment of nucleic acid that, taken as a whole, specifies a trait. Genes are contained in chromosomes, which are composed of DNA (deoxyribonucleic acid), a polymeric molecule found in cells of the body. DNA governs the production, growth and reproduction of the cells of the body. The current understanding of biological evolution, developed since Darwin’s time, recognizes the gene as a fundamental, if not the fundamental, unit of natural selection.

Functionally, genes pass traits from generation to generation. They do this by replicating themselves from parent to child. Physiologically, the same chemical structure appears in the child as was found in the parent. In combination with other genes and triggered by environmental influences, the genes cause the parent’s traits to appear in the child.

The term “trait” includes physical forms, such as bone density or eye color, behaviors such as sounding mating calls in certain seasons, and mental abilities or talents such as stereoscopic vision, empathy, or language.

Genes are not the only replicators. Ideas, symbols, behaviors, and other elements of culture replicate as well. Genes replicate from generation to generation; their cultural analogues, dubbed “memes,” replicate from mind to mind through writing, speech, gestures, rituals and the like.(6) The principles of evolution apply the same: like a gene, a meme is a replicator, except memes replicate contemporaneously between minds rather than historically between bodies.

Just as genes are subject to competition -- the ones that replicate to the next generation are those that help their host bodies to survive and reproduce -- so also are memes: only those that are catchy enough to secure attention in human minds replicate from mind to mind. What makes a meme catchy can be something as trivial as a memorable tune or limerick, or something that has continuing usefulness, such as ideas that hold cultures together.


So there is an abbreviated account of evolution. What does it mean for understanding human nature? To know what we are we must understand where we have come from. It is not just in our physical form that we have evolved, but in our mental capacities and in our cultures as well.

Are we, then, merely products of our evolutionary heritage, unable to change? No, but in our attempts to change, it certainly helps to understand what we have to work with. Understanding that inherited traits are the result of natural selection can help put in context findings about how we humans actually function in the world, a topic to which I intend to turn in future essays.

[Bill Meacham is an independent scholar in philosophy. A former staffer at Austin's 60s underground paper, The Rag, Bill received his Ph.D. in philosophy from the University of Texas at Austin. Meacham spent many years working as a computer programmer, systems analyst, and project manager. He posts at Philosophy for Real Life, where this article also appears. Read more articles by Bill Meacham on The Rag Blog.]

Notes

(1) See, for instance, the section titled “Predictive Power” in Wikipedia, “Evolution as fact and theory.”
(2) Dobzhansky, “Nothing in Biology Makes Sense Except in the Light of Evolution.”
(3) Idem.
(4) There are three sources of variation: mutation, gene flow and genetic shuffling through sexual reproduction. Mutation happens when environmental influences cause tiny changes in the chemical structure of genes, altering their functioning, or when cells divide and imperfectly replicate their DNA. By far the majority of mutations are destructive, degrading the gene’s ability to do its job of directing the growth of organs and characteristics, but some enhance that ability, or change it so that the result is advantageous. Gene flow refers to the transfer of genes between populations of an organism. Individuals from one population mate with individuals of another and transfer genes between them. Genetic shuffling through sexual reproduction causes the combination of genes in each child to differ from that of its parents. In species that reproduce sexually, each individual has two copies of every gene (specifically, each has two strands of DNA, each of which contains chromosomes, which contain genes). In sexual reproduction, the child gets some genes from the mother and some from the father, and the combinations vary with each child.
(5) Religious or mystical thinkers may postulate a divine purpose that guides the process of evolution, but the science of biological evolution does not need that hypothesis to explain the process.
(6) Dawkins, The Selfish Gene, chapter 11, pp. 189-201.

References

Dawkins, Richard. The Selfish Gene, New Edition. Oxford and New York: Oxford University Press, 1989.
Dobzhansky, Theodosius. “Nothing in Biology Makes Sense Except in the Light of Evolution.” American Biology Teacher vol. 35 (March 1973) reprinted in Evolution versus Creationism, J. Peter Zetterberg ed., ORYX Press, Phoenix AZ 1983. Available online at http://www.2think.org/dobzhansky.shtml as of 14 May 2012.
Wikipedia. “Evolution.” On-line publication, URL = http://en.wikipedia.org/wiki/Evolution as of 2 February 2009.
Wikipedia. “Evolution as fact and theory.” On-line publication, URL = http://en.wikipedia.org/wiki/Evolution_as_fact_and_theory as of 14 May 2012.
Wikipedia. “Meme.” On-line publication, URL = http://en.wikipedia.org/wiki/Meme as of 16 May 2012.

The Rag Blog

[+/-] Read More...

[+/-] Summary only...

Lamar W. Hankins : Darwin Day and Change We Can Believe In

Image from National Center for Science Education.
A solution to the post-Super Bowl blahs:
Darwin Day 2012

By Lamar W. Hankins / The Rag Blog / February 6, 2012

If you are having withdrawal from all the excitement of the Super Bowl, or if you just have the winter blahs, there may be a solution on the horizon. You can begin making preparations for Darwin Day 2012, which is scheduled for Sunday, February 12. Darwin Day is a global celebration of science and humanity held annually around the date of Charles Darwin’s birth -- February 12, 1809.

I’m sure you will want to participate in the ticker-tape parades held all around the country by entering a grand float in one near you. Great festivals should fill parks everywhere. The public speeches should be edifying. The abundance of food booths and vendors hawking their goods should be satisfying. The early-evening fire works displays should be spectacular. There is only one problem -- none of this will happen.

Only 16% of Americans in 2010, according to a Gallup Poll, believe in what it termed naturalistic evolution -- Darwin’s theory. It is unlikely that the remaining 84% will be interested in engaging in any celebrations of the great naturalist and scientist Charles Darwin.

Another 30% of Americans, according to Gallup, believe in what it termed Theistic Evolution. That is, “Man has developed over millions of years from less advanced forms of life, but God guided this process, including man's creation.” Of course, this isn’t exactly Darwin’s theory. A full 40% of Americans believe in creationism -- basically, the creation story as told in Genesis -- completely devoid of any mention of evolution.

My college experience introduced me to evolution indirectly. The biology courses I took at the Methodist-related college I attended were suppositioned on evolutionary theory as propounded by Charles Darwin, but his name was never mentioned. My two biology teachers were scientists, and they had no doubt about the scientific proof for evolution almost 50 years ago when I started college.

While some people thought the big bang was when I dropped a large tray full of plates and utensils in the dining hall, scientists understood that the big bang referred to the rapid expansion of the universe nearly 14 billion years ago. To understand the Big Bang (termed “The Great Radiance” by writer Philemon Sturges) requires knowledge of cosmology, astronomy, and physics at least.

Since I have no expertise in these fields, I look to the consensus among experts to decide what is true. Without question, there is considerable and, to scientists, convincing scientific evidence to support the Big Bang theory.

But Darwin did not study this theory. He studied nature and developed his own theory about the origin of species. A word about scientific theories might help get over the hump that some people think a theory is just an idea that may or may not be true. But this is how science works: A scientist (usually) proposes a theory to explain some natural phenomenon and then tests that theory. That’s what Darwin and thousands of scientists since the publication of Darwin’s 1859 book On the Origin of Species have done.

By its very nature, science is a field of study and inquiry based on proof and falsification of ideas. The nature of science is to engage subjects based on the truth or falsity of a proposition. The proof for evolution is now overwhelming.

Evolutionary biologists and those in related fields understand that the theory of evolution is indeed proven beyond any reasonable doubt. Since I am not a biologist, I think it is rational to accept the scientific consensus that evolution is true. About 98% of scientists in Texas, according to a 2008 poll, accept evolution to the exclusion of creationism, and 91% believe that evolution is compatible with religious faith.

Although it is impossible to watch human evolution in the span of a lifetime, or even 10,000 lifetimes, there are still ways to see evolution happening in a short span of time. A commonly known adaptation through natural selection is insects that are resistant to DDT and other pesticides. Gardeners and farmers know, also, about other insects that have adapted to other pesticides and pesky plants that have adapted to herbicides.

As evolutionary geneticist Jerry Coyne has pointed out, “fungi, worms, and algae have evolved resistance to heavy metals that have polluted their environment,” allowing them to survive these man-made poisons. Adaptation through natural selection is a part of Darwin’s original theory.

Many who argue against Darwin’s theory point to the fact that we have an incomplete fossil record to show all the developments from one species to another and within one species. Of course, the fossil record is incomplete, for natural reasons. Only species with certain characteristics can be preserved as fossils. And the conditions must be just right for a species to be preserved in sediment that becomes rock over millions of years.

For a fossil to be formed, the dead animal or plant must be in water, sink to the bottom, and be quickly covered by sediment before it decays or is scattered by scavengers. Dead plants and land-dwelling creatures rarely are found on the bottom of such water sources as lakes or oceans. Most fossils, then, are marine organisms.

To form a fossil, the hard parts of the organism become infiltrated or replaced by dissolved minerals, which becomes compressed into rock by an over-burden of sediment. Soft parts of plants and animals aren’t easily fossilized, so many species don’t become fossils.

Species such as worms, jellyfish, bacteria, and delicate creatures such as birds are much rarer to find as fossils, just as land-based species are harder to find than are aquatic species. With 10 million species now on earth and an estimated 17 million to 4 billion that once lived on earth, we will never find fossils of all species that have ever lived. We have found only 250,000 or so different fossil species, an inadequate sample for sure, but enough to figure out how the evolution of species proceeded and how major groups split off from one another.

I don’t know these things because I am a scientist. I accept these views because the overwhelming consensus among all the world’s biological and related scientists supports these propositions. That consensus exists because it is supported by the evidence.

A friend of mine asked me recently to explain evolution in one sentence or short paragraph. I’ll leave that task to Jerry Coyne, who explains the modern theory of evolution with one long sentence:

Life on earth evolved gradually beginning with one primitive species -- perhaps a self-replicating molecule -- that lived more than 3.5 billion years ago; it then branched out over time, throwing off many new and diverse species; and the mechanism for most (but not all) of evolutionary change is natural selection.

In addition to genetic change over time, usually a great time, mutations develop in response to evolutionary pressures. Such change over time is called gradualism. It may take hundreds of thousands of generations, even millions of generations to develop the distinct species we see today. This development occurs through another concept of evolution termed splitting, or speciation.

A fourth axiom of evolution is common ancestry, which can be determined through fossil evidence or DNA evidence, which Darwin did not have over 100 years ago, when he developed his theory.

The fifth part of Darwin’s theory is natural selection, which does not produce the fittest, as is commonly thought, but produces the fitter -- improvements over what came before.

And then there are other causes for evolutionary change, such as random changes caused by different families having different numbers of offspring, which has nothing to with the adaptation caused by natural selection. And there are other factors, such as genetic drift, which is a random change in the frequency of genes in an isolated group, which is not caused by natural selection.

It may help some people understand evolution better to know that the evidence shows that the first organisms on the earth were simple photosynthetic bacteria that were followed 2 billion years later by more complex organisms. About 600 million years ago, simple multicelled organisms developed (including worms, jellyfish, sponges).

Land-based plants and tetrapods appeared about 400 million years ago, and then came amphibians, reptiles, birds, mammals, and insects millions of years later.

Humans appeared on the earth about 7 million years ago. All of the evolution evidence supports the view that humans were and are subject to the same evolutionary processes that affect all other species.

My college biology professors, who offered no apologies for teaching evolution as fact, suggested that there was no inconsistency between belief in God and evolution. Belief in God is based on faith. Evolution is based on science; that is, it is testable and permits making verifiable predictions. Belief in God is not testable and thus is not the subject of much scientific inquiry.

In the same way, “intelligent design theory” or “creationism,” as it was originally called, also is not subject to testing and falsification because it is a faith-based, non-scientific theory. No one can test the belief that God created the earth and all of its inhabitants in six days 10,000 years ago. What we know is that the available empirical evidence establishes that organisms have existed on earth for 3.5 billion years.

Texans polled about evolution have opinions near the same figures as for the country as a whole, though about 25% fewer Texans accept Darwinian evolution. Nearly 1/3 of Texans believe that humans and dinosaurs roamed the earth together, leading the comedian Lewis Black to quip that apparently a significant proportion of people think that “The Flintstones” was a documentary.

Over 100 years after publication of On the Origin of Species (the last edition was called The Origin of Species) and 87 years after the Scopes trial, over half of Americans do not accept any sort of evolution. It causes one to wonder if perhaps Americans don’t evolve.

Nevertheless, Charles Darwin has helped us, perhaps more than any other scientist, to understand critical facts about the natural world. For this, we should celebrate his achievements. I and many others will be celebrating him in one way or another on Darwin Day 2012 -- even in the state of Tennessee, where the Scope’s trial was held.

Some of us will join one another for a meal, which can be fittingly preceded by Philemon Sturges’s singing grace, which acknowledges the essence of evolution, sung to the tune of “We Gather Together”:

We gather together to feast and be joyful
Earth's bounty is precious for we are all one
So eat with Thanksgiving; this food was once all living
Sing praises to the life that becomes now your own

Happy Darwin Day! And many happy returns.

[Lamar W. Hankins, a former San Marcos, Texas, city attorney, is also a columnist for the San Marcos Mercury. This article © Freethought San Marcos, Lamar W. Hankins. Read more articles by Lamar W. Hankins on The Rag Blog.]

The Rag Blog

[+/-] Read More...

[+/-] Summary only...