2.2 DARWIN AND THE ORIGIN OF SPECIES

I. PRELUDE TO DARWIN

In the previous section on the history of evolutionary thought, we traced the development of many of the ideas leading to a clearly defined theory of evolution. The formalized study of geology led to the realization of an ancient, restless earth with 'no vestige of a beginning, no prospect of an end.' Rigorous classification of life on earth implied common evolutionary origins for similar creatures. Systematic assembly of fossil bones revealed creatures no longer living today. Knowledge of the world was increasingly secular, free of scriptural constraints.

There was increasing evidence that species might not be fixed. Some of the best evidence came from pigeon fanciers who could dramatically alter pigeons in just a few generations. Lamarck had proposed the theory of acquired characteristics. It said that a trait acquired by an animal during its lifetime could be passed on to offspring. Yet, experiments with rat tails and experience with circumcisions refuted the Lamarck hypothesis. Breeders were the agencies of change with pigeons, but what about in the wild? The answer came from a clergyman concerned about the poor, one of the legendary figures of the 'dismal science' which we call economics.

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II. THOMAS MALTHUS: LIFE IS A STRUGGLE

Unlike the other figures in this brief history of evolutionary thought, Malthus was not a natural scientist. He was a social scientist before such a field was recognized. His concern was about the poor in society and why they were poor. He approached the problem from mathematics and published An Essay on the Principle of Population. He saw that animals--and people can reproduce faster than their food supply.

Population size increases geometrically (1.2.4.8.16) while the available food supply increases only arithmetically (1.2.3.4.5). No matter how much food is supplied, the number of mouths to feed will increase ever faster. Poverty, pestilence and warfare are the inevitable constraints on population according to Malthus.

The Malthusian idea caught on quickly. Life was a struggle. The weak fall behind and die. Only the strong survive. Now there was a mechanism for evolution. Life was a struggle and only the fittest would survive. The idea for the basis of evolution had come from a clergyman.

The Malthus idea solved the problem of how evolution worked for Alfred Wallace and Charles Darwin, but the essay was originally written about the problem of overpopulation.

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Was Malthus correct? World population today is vastly larger today than it was 200 years ago and hunger seems a problem of politics and distribution, not a shortage of production. Intensive agriculture has more than kept up with demand.

The science fiction writer Isaac Asimov came up with this interesting calculation: if world population doubles every 35 years, in 6,826 A.D. the mass of humanity will equal the total mass of the universe . . . an impossibility.

The rate of population growth as of 1998 is declining. According to the U.S. Census Bureau, fertility--the number of children born per woman during her lifetime has declined since 1985 from 4.2 to 2.9. There are now 79 countries representing 40% of the world's population where fertility rates--if they continue--will lead ultimately to population decline. Already, 15 countries--many in Western Europe--now fill more coffins than cradles. The 'birth-dirth' has even spread to many developing countries. Fertility and the choice to have children are a very complex issue that confounds even the most sophisticated demographers.

In this country, primary and secondary schools are experiencing increases in student numbers as 'generation X' winds its way through the demographic landscape. This bodes well for graduating orthodontists.

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III. UNIFORMITARIANISM: SLOW ACTING FORCES CAUSE BIG CHANGES

Another Scotsman, Charles Lyell had a direct impact on Darwin as a friend and mentor. Lyell was a barrister by training but a geologist by avocation. His three volume Principles of Geology went with Darwin on the Beagle. He demonstrated that forces such as wind, water erosion, local flooding, frost, volcanoes, earthquake and glaciers all contributed to present day landscapes. It further confirmed the immensity of deep time for the inherently slow processes of evolution to take place.

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IV. IT COMES TOGETHER / CHARLES DARWIN

Born in 1809, the son and grandson of distinguished physicians, Darwin seemed destined to also have a career in medicine. His grandfather was imposing in intellect and size and was a well-respected intellectual in his own right. Erasmus Darwin was so overweight that he had a semicircle cut out of his dining room table to accommodate his rotund figure.

Darwin hated medicine and for a time-studied theology. He nevertheless continued his interest in natural history and frequently went on field trips with Reverend John Stevens Henslow, professor of botany. It was Henslow who recommended Darwin for passage on the Beagle in the unpaid position of naturalist and ship's companion. The Beagle was commissioned by the British Navy for a mapping survey of the coast of South America. The famous voyage lasted almost five years and forever changed both Darwin's life and that of science itself.

On the volcanic Galapagos Islands off of South America, Darwin saw finches and tortoises adapted to life on the varying conditions of the different islands. In time he came to understand them as evolutionary adaptations of similar species on the mainland. Although seasick most of the time, he collected specimens and sent his written descriptions off to Henslow. Extracts of those letters were read at scientific meetings. Darwin, unknown to him, was emerging as a respected scientist back home. Aboard ship, he also studied the freshly published Lyell's Principles of Geology.

Darwin returned to England in 1836, married his first cousin Emma Wedgewood, and was immediately accepted into the most prestigious scientific circles. Two years later, he read the Malthus essay. It struck him at once that in nature, favorable variations would survive and unfavorable ones would be destroyed. Species were mutable, not fixed.

On the Galapagos Islands, tortoises had become big and filled the role of large herbivores. In Australia, marsupials had diversified into roles filled by mammals on other continents. On New Zealand, large flightless birds emerged into niches normally filled by mammals elsewhere.

For several years, Darwin refined his ideas and corresponded with friends, but he hesitated to come forward. He realized that natural selection would be a bombshell. Then, fate intervened. He could not remain silent and fail to be recognized for his work. Someone else had also worked out survival of the fittest.

In 1858, Alfred Wallace, a self-taught collector and naturalist sent Darwin a copy of his own paper describing evolution driven by competition and natural selection, Wallace also had read Malthus. Darwin realized that Wallace could publish and claim credit for 'his' theory.

What to do? Papers by both Wallace and Darwin were presented jointly before the Linnean Society of London in 1858. Neither author was present. The papers received little notice. However in 1859, Origin of Species was published and the storm broke. Within a few years it won virtual acceptance in the field of biology.

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V. THE THEORY OF EVOLUTION

We have emphasized that a hypothesis should be testable, subject to falsification or verification. Some critics attack 'evolution' as only a theory. If we call it theory, that doesn't diminish its veracity as truth. It identifies it as a statement for scientific inquiry and that it must stand or fall on the strength of the evidence. First, let us examine the theory. It has several components. But don't take my word for it. Look at them. What do you think?

(1) Species have great potential fertility. If a quarter pound fish can lay 8000 eggs per year, in ten years their total weight will be 2.3 x 10 tons--about equal to the mass of the sun.

(2) In nature, populations stay relatively stable, within limits. When animals are placed outside of their natural habitats, sometimes their numbers can grow to Biblical proportions. This happens with introduced mammalian rats and mice occasionally in Australia. Usually, however, there are limits on population size.

(3) Food resources are limited.

The inference from these is this: In an environment of stable resources and overproduction of individuals, there will be a struggle for survival. Only the fittest will survive.

(4) No two individuals are identical. Variation is the wellspring from which species change can emerge.

(5) Variation is heritable. Offspring inherit from their parents.

Two inferences can be deduced from these observations. In a world where individuals must struggle to survive, those with the best characteristics will survive to pass them onto their offspring. Given time, natural selection will result in the emergence in a new species. Tiny changes will accumulate over time.

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VI. DARWIN'S EVIDENCE.

Let me emphasize again, Darwin didn't just have a bad night and hatch all of this on a whim. It is very tightly reasoned both internally and in its empirical evidence. It ties together existing evidence and suggests new lines of inquiry. What evidence did Darwin cite?

(1) Domestication of plants and animals.

Darwin was a pigeon fancier. As wild or feral birds, pigeons seem to 'hang around' humans. They aren't 'spooked' by humans and are easy to trap. They can be eaten, used as homing pigeons, or admired as fancy breeds. They have been developed into a variety of shapes, colors, styles, and sizes. They all stem from one breed, Columba domestica. Pigeons are the product of controlled evolution. The breeder is the agency of selection.

(2) Geographic distribution of life forms.

In Australia, marsupials radiated into various niches and became marsupial versions of mice, wolves, cats, bears, and evened a copy of the aberrant lemur, the aye. In New Zealand, birds free of competition, filled the niches occupied by marsupials in Australia and mammals elsewhere.

(3) Geology and fossils.

Darwin found a long extinct Megatherium fossil in South America and sent it home. It was an instant sensation. In geology, the more recent layers are near the top. Lower ones are older. The deeper the layer, the more unlike current living species were the specimens found. The Grand Canyon is a vivid example: it is a slice through time.

(4) Comparative anatomy.

The forelimbs of the frog, lizard, bird, human, cat, whale, and bat--just to name a few, all contain a humerus, radius, ulna, carpals and phalanages. They are variations on a skeletal theme.

Evolutionary theory explains why they are similar: they share a common origin and why they are different: evolutionary adaptation to a different environment.

(5) Embryology.

Long ago, embryologists noticed the remarkable similarity amongst vertebrate embryos that were strikingly different as adults. It appears that organisms that share a common descent make use of shared developmental plans. To say that 'ontogeny recapitulates phylogeny' probably overstates the case. Yet, at early stages, humans and other vertebrates are strikingly similar.

(6) Vestigial Organs..

Blind cave fish retain the rudiments of eyes even though sight was lost long ago. Some seals and 'toothless' whales have tooth development in utero even though they subsequently resorb and the creature is functionally without teeth in adulthood.

These evidences are explained by the theory of evolution. Evolutionary theory makes them understandable. The helps us make sense of the universe

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VII. EVIDENCE THAT WE CAN SEE

(1) The British Peppered Moth.

The peppered moth in England comes in two colors, light and dark. About 1% of offspring are dark, a disadvantage in camouflage on light bark. Birds prey on them. During the Industrial Revolution, soot darkened tree bark. More dark moths survived. They were selected for favorably. In today's coal free environments, soot has lessened, tree bark has lightened, and light peppered moths are again favored.

(2) Antibiotic resistance. Some cynics call this 'the revenge of the germs.' Aided by their genetic versatility, antibiotic resistance by microbes has increased rapidly in recent years to many of our finest antibiotics. Synercid remains the last antibiotic available that is effective against some of the most virulent antibiotic resistant strains. Even some herpes simplex virus is not resistant to Acyclovir. It is survival of the fittest at the microbial level.

(3) Darwin's finches revisited.

Modern day studies of Galapagos finches show that beak size changes over time in direct response to changes in environment. Beaks get larger in periods of drought. Those with the bigger beaks can crack open tougher seeds during dry periods.

 

(4) Resistance by insects to insecticides. Malaria was eradicated in this country with DDT after World War II. It is now banned for ecological reasons, but when still in use, resistance by anopheles mosquitoes was emerging. Resistance to pesticides in countries with endemic malaria is an alarming problem.

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VIII. DARWIN IN ENGLAND

Darwin's life after his return from world travel aboard the Beagle is somewhat of a mystery. In his later years he suffered panic attacks, agoraphobia, fears of crowds, travel, and being alone. He declined an invitation by saying: "How I wish I could accept your invitation and pay you a visit, but I have found it impossible to visit anywhere; the novelty and excitement would annihilate me."

Starting a year or so after the trip on the Beagle, and for the rest of his life, he had repeated attacks of palpitations, shortness of breath, lightheadedness, trembling, crying, the sensation of dying, and fear of losing control.

He isolated himself with Emma and his children in the country at Down House 16 miles from London and refused invitations to lecture or to be with colleagues. Darwin himself said the 'even ill-health though it has annihilated several years of my life, has saved me from the distractions of society and its amusements.

Despite his illness and the death of three children, his wife Emma imposed order and discipline on the household. He was a patient family man and helped raise ten children.

For four hours each day, Darwin would retreat to the study. His skill lay in piecing together seemingly unrelated patterns and teasing out a single thread. He raised flocks of pigeons and studied their remains on his billiard table. To test the hearing of worms, he placed several in a jar, propped them on the piano and played them ditties. He built a thinking path on his estate where he pondered his theories and observed birds.

HMS Beagle, 1932

Surrounded by books and specimens, he pondered the theory of evolution and waited 20 years before publishing. He was terrified of the religious consequences. His home at Down, now restored, was reopened to the public on Good Friday, 1998.

..... CJ'98

Resources

Campbell, G. and Loy, J. Humankind Emerging, 7th ed New York: HarperCollins College Publishers, 1996.

Caras, R. A Perfect Harmony. New York: Simon and Schuster, 1996.

Edey, M. and Johanson, D. Blueprints, Solving the Mystery of Evolution. New York: Penguin Books USA Inc, 1989.

Naik, G. 'Darwin's Home: Made Fit to Survive' Wall Street Journal. April 28, 1998.

Selkirk, D and Burrows, F. Confronting Creationism: Defending Darwin. Kensington: New South Wales University Press, 1988.

'Too Many People? Not By a Long Shot' Wall Street Journal 10 February 1997.

Relethford, J. The Human Species. Mountain View, Mayfield Publishing Company, 1997.

Turnbaugh et al Understanding Physical Anthropology and Archaeology, 6th ed. Minneapolis/St. Paul: Westview Publishing Company, 1996.