Main Theories of Evolution

"The great tragedy of Science — the slaying of a beautiful hypothesis 

by an ugly fact."

 

T.H. Huxley

  • Many biologists has postulated different mechanism other than the Darwin’s theory, before or after Darwin published his book. Additional to natural selection, I will review several major hypotheses on the issue and introduce briefly main ideas of creationism and intelligent design at the end.
A. Natural Selection-Darwinism
  • The concept of evolution was not completely new, when Charles Darwin stunned the world with his revolutionary views. Europeans in the late 17th century were widely discussing evolution in broad terms. Several thinkers, including Darwin’s own grandfa­ther, had proposed evolutionary ideas. In 1859, Darwin published The Origin of Species by Means of Natural Selection, in which he summarized all the evidence supporting the idea that all organisms were descended with modification from a common ancestor. In addition, he proposed that natural selection was the mechanism of speciation. The theory of natural selection is very simple. All organisms had variations in their characteristics, such as strength, height or speed. Organisms with certain characteristics enjoyed advantages over their peers who did not possess them. For instance, if a new color provided better camouflage for moths, then moths with the color would live longer and produced more offspring. If the variation were inherited, then the organism’s characteristics would change over time. If those changes met certain criteria, a taxonomist would classify it as a new species.
  • In Darwin’s era, the principles of genetics had not been defined. Scientists did not know how characteristics were passed from parents to offspring. At that time, pangenesis was a popular theory on hereditary. It stated that hereditary information was carried by tiny particles that bud from cells throughout a person’s body. These particles or ‘gemmules’ migrated into the reproductive organs prior to fertilization. Thus, every cell in the body contributed to the constitution of the offspring. Pangenesis was the foundation of natural selection. Unfortunately, many biologists did not recognize it.

B. Use-inheritance –Lamarckism

  • Jean Baptiste de Lamarck (1744 - 1802) was the first one to initiate a theory to explain how and why evolution occurs. In his Philosophie Zollogique (1809), he introduced idea of vitalism to explain a species' ability to adapt. It is better known as the theory of inheritance and of acquired characteristics. According to this view, certain traits of an organism arise via use or disuse. When a trait was used many times, organs with the trait grew stronger, which made the trait commonplace. On the hand, a trait that was not used caused the corresponding organ to weaken and it was not passed on the organism’s offspring. For example, a giraffe developed a long neck from the need of leaves on treetops. Over time, the giraffe's neck muscles were strengthened to support long necks; hence, its offspring were also endowed with long necks. Since then, these notions have been disproved.
  • August Weismann, a German biologist, amputated the tails of 901 young white mice in 19 successive generations. Yet, each new generation of mice had full-length tails. In the final generation, the tails were as long as ones originally measured on the first generations. Popularity of Lamarckism declined rapidly with the advent of molecular biology. Molecular biologists concluded that hereditary information flows only from the nucleic acid to the protein, never in the reverse direction. This implied that changes in the genetic apparatus could only arise through by errors in replication and variation had to be accidental.

By Lamarkism, giraffe's neck was enlonged  by

its repeated use.

C. Geographical isolation

  • Speciation by geographical isolation (GI) or allopatric speciation was initially proposed by Dr. Mayr at Harvard University. By his and its advocates' view;

"When part of a population of the same species becomes geographically isolated from the remainder, it may over time evolve characteristics different from the parent population (due to natural selection). This is particularly likely to happen if the isolated population is small, because of founder effects, or if the population become isolated in an environment which makes new demands upon it."

"As a result of the loss of genetic variation, the new population may be distinctively different, both genetically and phenotypically, from the parent population from which it is derived. In extreme cases, the founder effect is thought to lead to the speciation and subsequent evolution of new species."

  • However, the resulted subpopulation from founder effect still belongs to the original population, how, why and when do they become a different species? Robinson Crusoe was still a human being after spending 28 years on a remote tropical island. How would his offspring become non-human after many generations, assuming that he would have a female pattern? The author did not explain it, just tell us it so, and he did not solve the old problem, but create new ones.

Founder effect narrows genetic variations in subpopulatiion,

but not leads to speciation.

"If there is sufficient genetic change following geographical isolation, then if the geographical barriers are removed (perhaps due to human activity), members of the two populations will be unable to successfully mate with each other. At this point, a new species has emerged."

  • The question is what kind of genetic change is sufficent, many genetic differences exist within any organism population, such as height, weight, color, hair, etc. Are these changes in genetics sufficient? The author does not answer these basic questions, only open a new door for imagination.

D. Genetic drifting

"Genetic drift (GI) is the process of change in allele frequencies that occurs entirely from chance....The concept was first introduced by Sewall Wright in the 1920s, and is now held to be one of the primary mechanisms of biological evolution."

"Genetic drift has important implications for evolution and the process of speciation. When a small group of individuals becomes isolated from the majority of individuals of a species, the small group will genetically drift from the rest of the species. Because genetic drift is random and the smaller group will drift more rapidly than the larger group, it is possible that, given enough time, the small group will become different enough from the large group to become a different species."

Genetic drifting explains how allele fixed in small population, but does not tell how new species originated.

  • The question is even the small group of individuals becomes isolated, what kinds of things will be considered enough for them become a different species? How do these things happen? Does it happen individual or in group? If it occurs individually, how does the newcomers find out a pattern to mate? If it occurs in a group, how does a similar mutation occur in a group?
  • All of these question are basic components for a sound theory of speciation. The theory does not contain any of these, but leaves public to have wide guess.
  • It is agreed that existence of different GI, NS, GD, the argument is the role of these mechanisms in speciation, not if they occur? The Sun arises from the East, Bush was elected as the President and Gore lost. The rise of the Sun has not lead to Gore's loss, the same logic apply to these theories.
  • E. Speciation by macromutation

    • Unsatisfied with the Darwinian theory, various mechanisms of speciation have been proposed with the aim to replace it with one that is more plausible. In 1886, Darwin's research associate George Romanes published a paper entitled Physiological Selection: An Additional Suggestion on the Origin of Species, in which he proposed a mechanism of evolution: two organisms underwent the same type of variation in germ line cells, and would still be fertile or have "physiological complements" between them. He suggested that germ line cells, like cells of all other organs and tissues, might undergo random variations.
    • One of the first to recognize the evolutionary significance of chromosomes was the geneticist Richard Goldschmidt. He devoted his early career to the genetics of the silkworm moth. Goldschmidt was struck by a pattern of discontinuity in his investigations.After 25 exhausting years of work, Goldschmidt decided that he must establish a different way that cross-species evolution could occur.He announced his new concept: a megaevolution in which one life form suddenly emerged completely out of a different one, he called them "hopeful monsters".

    Goldschmidt proposed that new species suddenly emerged as "hopeful monsters".

    F. Modern synthesis

    • During the first part of 20th century, the incorporation of genetics and population biology into studies of evolution led to a Neo-Darwinian theory of evolution that integrated genetic mutations with Darwin’s theory. Natural selection then became a process that altered the frequency of genes in a population. The ideas were formulated from several disciplines, including biogeography, systematics, and population genetics. New discoveries have continued to be introduced to it. In the original version of the modem synthesis, natural selection was the major cause of evolution at all levels. Populations adapted by natural selection, new species arose when isolated populations diverged as different adapta­tions evolved, and continued divergence due to natural selection differentiated the higher taxa. Modern syn­thesis recognizes how genetic drift can cause rapid, nonadaptive evolution. However, the major emphases of the synthesis are gradualism and natural selection.

    Development of Modern Synthesis

    G. After modern synthesis

    • By the 1970s, an increasing number of paleontologists had become dissatisfied with this approach, because many of the classic examples of gradual change had not withstood the test of modem techniques. If no genuine cases of gradualism existed, then the argument for treating all cases of sudden change as the result of imperfect evidence was undermined. It might be better to reexamine the evidence in a new light, putting aside the traditional Darwinian assumption of gradualism and choosing instead a model of evolution that would allow for the sudden appearance of new forms as indicated by the fossil record.

    • In 1972, Niles Eldridge and Stephen Gould revived this idea under the name Punctuated Equilibrium (EP). They agreed that transitional fossils were very rare, and they were not as common as the selectionists predicted. A species goes unchanged for a long time before it is replaced without any transition by a new species that resembles a variation of the old one. They surmised that a group of creatures was separated from the rest of their species; since the group probably lived in a small inhospitable fringe area, they would be under selection pressure. As a small group, they were able to evolve quickly. Later, they spread, and replaced their parent species.
    • The theory of punctuated equilibria provides paleontologists with an explanation for the patterns found in fossil records. However, punctuated equilibria have one major defect: it does not provide a coherent biogenetic mechanism to explain how organism at peripheral environments evolves such rapidly.

    Nonscientific theories on speciation

    • According to a recent Gallup poll (2001), Americans are about equally split regarding evolution. About 49% believe in evolution and 45% believe in special creation, while 37% of those who believe in evolution also believe God guides the process. Phillip Johnson, a professor of law at the University of California Berkeley,has written several books aimed at providing anti-evolutionary apologetics, including one of the most cited recent anti-evolutionary works, Darwin on Trial. Impotence of Darwinism, and lack of alternative, sound scientific theory not only make most of public skeptical of the mechanism, but also put whole idea of evolution in a fragile position.

    Creationism

    • Prior to the mid 1800s, scientists firmly believed that a Master Designer made all creatures. Those pioneers who laid the foundations of modern science were creationists. According to the Bible,humans, animals, and the rest of the universe were created in a six- day period 6,000 years ago. Those who believe this version of our origins are called creationists. Creationists believe not only that each species was specially created, but also that evolution did not and could not have happened. William Paley (1743-1805), in Natural Theology,summarized the viewpoint of the scientists. He argued that the carefully designed structures of organisms clearly point to a Designer. If we see a watch, we know that it had a designer and maker. This is known as the "argument by design." Although we could ignore or ridicule these theories, but our scoffing does not change the situation.
    • Doctoral scientists to conduct research on the topic of the creation-evolution founded Creation Research Society in 1963. In 1972, Henry Morris founded the Institute for Creation Research (ICR) in El Cajon, California. It has become the leading anti-evolution organization in the world since then. The linking of speciation with the Bible has allowed creationism to be challenged as a dis­guised form of religion. Many Christian denominations do not believe that the Bible should be taken literally on scientific matters and condemn fun­damentalists for their oversimplification of the relationship between God and man. Many religions do not condemn evolution, because they do not believes creatures in the world rest on a single act of creation. 

    Many creationists believe all organism in the world created by God in 6 days

    Intelligent Design

    • Disappointed with the fundamentalist interpretation of the Bible by creationism, a group of scientists with different backgrounds launched the Intelligent Design movement. Phillip Johnson, a law professor at the University of California at Berkeley is the founder of the movement. While on sabbatical in the late 1980s, he studied the scientific case for and against Darwinism and concluded that the empirical case for Darwinism was surprisingly weak, and Darwinism lacks crucial evidence, begs important questions, and often caricatures alternatives unfairly. The proponents of ID make their case against Darwinian evolution by pointing out flaws in the arguments and gaps in the evidence, not by basing on religious texts. Neither do they argue that the Earth is only about 6,000 years old, nor do they care to discuss Noah's flood. That is how they are different from the older "scientific creationism" movement. 
    •  The arguments of the ID advocates may seem like a rehash of the creationists, but the advocates of ID declare that they do not reject evolution simply because it does not fit with their understanding of the Bible. Two scientists often cited by defenders of ID are Michael Behe, author of William Dembski, author of Intelligent Design: The Bridge between Science and Theology (1998). Dembski and Behe are fellows of the Discovery Institute, Seattle research institute funded largely by Christian foundations. Their arguments are attractive because they are couched in scientific terms and backed by scientific competence. However, they mainly try to find weaknesses in natural selection, rather to explain the scientific base of their own. 

    • Two major issues arise from Creationism and the Intelligent Design movement. Firstly, they have established the controversy as a dichotomy between “atheistic evolution” and “biblical-literalist Christianity”. Thus, any criticisms against evolution can automatically construed evidence for their ideas. If the issues posed by creationists were contrary to natural selection, then it might be revised or replaced by another scientific theory. Secondly, Creationism and Intelligent Design lack persuasive power, as they do not provide any guide how to further study evolution. Accepting either Creationism or Intelligent Design implies that the question has been answered. The Supernatural created all creatures in the world, and further scientific investigation beyond descriptive study is not possible. Frankly speaking, the majority of Intelligent Design advocates are not religious zealots. Most of their arguments against the Darwin’s theory are scientifically sound, because the theory does not provide a reasonable explanation for how the new species arise. It is the failure of the theory and the void of alternatives forces them to look for nonscientific explanations.

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