It is time for students of the evolutionary process, especially those who have been misquoted and used by the creationists, to state clearly that evolution is a fact, not theory, and that what is at issue within biology are questions of details of the process and the relative importance of different mechanisms of evolution. It is a fact that the earth with liquid water, is more than 3.6 billion years old. It is a fact that cellular life has been around for at least half of that period and that organized multicellular life is at least 800 million years old. It is a fact that major life forms now on earth were not at all represented in the past. There were no birds or mammals 250 million years ago. It is a fact that major life forms of the past are no longer living. There used to be dinosaurs and Pithecanthropus, and there are none now. It is a fact that all living forms come from previous living forms. Therefore, all present forms of life arose from ancestral forms that were different. Birds arose from nonbirds and humans from nonhumans. No person who pretends to any understanding of the natural world can deny these facts any more than she or he can deny that the earth is round, rotates on its axis, and revolves around the sun.
The controversies about evolution lie in the realm of the relative importance of various forces in molding evolution.
- R. C. Lewontin "Evolution/Creation Debate: A Time for Truth" Bioscience 31, 559 (1981) reprinted in Evolution versus Creationism, op cit.
This concept is also explained in introductory biology books that are used in colleges and universities (and in some of the better high schools). For example, in some of the best such textbooks we find:
Today, nearly all biologists acknowledge that evolution is a fact. The term theory is no longer appropriate except when referring to the various models that attempt to explain how life evolves... it is important to understand that the current questions about how life evolves in no way implies any disagreement over the fact of evolution.
- Neil A. Campbell, Biology 2nd ed., 1990, Benjamin/Cummings, p. 434
Also:
Since Darwin's time, massive additional evidence has accumulated supporting the fact of evolution--that all living organisms present on earth today have arisen from earlier forms in the course of earth's long history. Indeed, all of modern biology is an affirmation of this relatedness of the many species of living things and of their gradual divergence from one another over the course of time. Since the publication of The Origin of Species, the important question, scientifically speaking, about evolution has not been whether it has taken place. That is no longer an issue among the vast majority of modern biologists. Today, the central and still fascinating questions for biologists concern the mechanisms by which evolution occurs.
- Helena Curtis and N. Sue Barnes, Biology 5th ed. 1989, Worth Publishers, p. 972
One of the best introductory books on evolution (as opposed to introductory biology) is that by Douglas J. Futuyma, and he makes the following comment:
A few words need to be said about the "theory of evolution," which most people take to mean the proposition that organisms have evolved from common ancestors. In everyday speech, "theory" often means a hypothesis or even a mere speculation. But in science, "theory" means "a statement of what are held to be the general laws, principles, or causes of something known or observed." as the Oxford English Dictionary defines it. The theory of evolution is a body of interconnected statements about natural selection and the other processes that are thought to cause evolution, just as the atomic theory of chemistry and the Newtonian theory of mechanics are bodies of statements that describe causes of chemical and physical phenomena. In contrast, the statement that organisms have descended with modifications from common ancestors--the historical reality of evolution--is not a theory. It is a fact, as fully as the fact of the earth's revolution about the sun. Like the heliocentric solar system, evolution began as a hypothesis, and achieved "facthood" as the evidence in its favor became so strong that no knowledgeable and unbiased person could deny its reality. No biologist today would think of submitting a paper entitled "New evidence for evolution;" it simply has not been an issue for a century.
- Douglas J. Futuyma, Evolutionary Biology, 2nd ed., 1986, Sinauer Associates, p. 15[/b]
Hey Bakes here is some SCIENCE for you...thoughts/
Consanguinity – Inbreeding
Definition of Consanguinity – Inbreeding
Inbreeding is the production of offspring by the mating of closely related individuals. This practice provides a greater chance for recessive genes to be expressed phenotypically. In humans, the amount of inbreeding in a specific population is largely controlled by traditional and cultural practices.
Description of Consanguinity – Inbreeding
In Europe and North America, the marriage between close relatives is strongly discouraged by social convention. However, this is not true in many parts of the world. Marriage between close relatives is common in areas of the world in which geographical or ethnic isolation make marriage to unrelated people difficult.
The majority of serious genetic disorders are recessive, which means that an individual must inherit two copies of the abnormal gene (one from each parent) for the disorder to be expressed.
It is much more likely that both parents will carry the same recessive gene if the parents are related. The risk of a serious disease or malformation in a child of such a union is about 1 in 20. However, among married first cousins, the risk increases to about 1 in 11. If the couple are first-degree relatives, the risk is 1 in 2.
Cultural taboos are only loosely related to risk. The marriage of double-first cousins is just as risky (from a genetic standpoint) as it is in the marriage of a half-sister and a half-brother. However, in most places, the former is legal and the latter is not.
In cultures without significant inbreeding, the distribution of recessive disease genes will no longer be random and the genes will be concentrated in the more inbred families. An unexpected observation has been that non-consanguineous marriages in such cultures actually have a lower rate of genetic disorders than couples in cultures where close inbreeding is not socially acceptable.
For example, non-consanguineous Pakistani couples in Britain have fewer disabled children than their British counterparts. At first glance, it might seem that the line of inheritance on an inbred family with a serious disease gene might simply die out. However, there is some evidence to suggest that closely related couples are, in fact, more fertile than unrelated couples. Therefore, although any individual child is less likely to be healthy, more children are produced, and the net result is roughly the same. In such cultures, some social advantages of marrying close relatives, in terms of maintaining family wealth and relations between groups, may outweigh biological disadvantages.
Consanguinity and Birth Defects
Some birth defects can be inherited, meaning that the hereditary information is passed from parent to child by genes located on the chromosomes found in cells.
Normal body cells have 46 chromosomes, except for the reproductive cells (the sperm and egg) which have only 23 chromosomes each. At conception, each parent normally contributes 23 gene-carrying chromosomes to the hereditary make-up of the child.
In some cases, one affected parent has a faulty gene which dominates its normal counterpart, and each child has a 50 percent chance of inheriting the faulty gene and the disorder. This is known as dominant inheritance. Huntington's disease and Marfan syndrome are examples of genetic conditions that are transmitted this way.
In other genetic disorders, both parents (apparently normal) carry the same abnormal gene. Each child that is conceived has:
a 25 percent risk of receiving that gene from both parents (in which case, the particular birth defect may occur)
a 25 percent chance of inheriting the two normal genes and remaining unaffected
a 50 percent chance of inheriting one faulty and one normal gene (becoming a carrier without the disorder, just like the parents). This type of inheritance is called recessive inheritance.
Cystic fibrosis and Tay-Sachs disease are transmitted as recessive disorders. Therefore, the chance of inheriting a recessive disorder is increased in a child whose parents are "blood" relatives (consanguineous).
