acmilan said:
A number of different theories exist, most people just believe Darwin/Wallace's is the only theory that has any credible evidence. No evidence has been found to prove Darwin's, nor any other theory of evolution proposed as completely correct.
Claim:
Evolution is only a theory. It is not a fact.
Response:
1. The word "theory," in the context of science, does not imply uncertainty. It means "a coherent group of general propositions used as principles of explanation for a class of phenomena" [Barnhart 1948]. In the case of the theory of evolution, the following are some of the phenomena involved. All are facts:
- That life appeared on earth more than two billion years ago;
- That life forms have changed and diversified over life's history;
- That species are related via common descent from one or a few common ancestors;
- That natural selection is a significant factor affecting how species change.
- Many other facts are explained by the theory of evolution as well.
2. The theory of evolution has proved itself in practice. It has useful applications in epidemiology, pest control, drug discovery, and other areas [Bull and Wichman 2001; Eisen and Wu 2002; Searls 2003].
3. Besides the theory, there is the fact of evolution, the observation that life has changed greatly over time. The fact of evolution was recognized even before Darwin's theory. The theory of evolution explains the fact.
4. If "only a theory" were a real objection, creationists would also be issuing disclaimers complaining about the theory of gravity, atomic theory, the germ theory of disease, and the theory of limits (on which calculus is based). The theory of evolution is no less valid than any of these. Even the theory of gravity still receives serious challenges [Milgrom 2002]. Yet the phenomenon of gravity, like evolution, is still a fact.
5. Creationism is neither theory nor fact; it is, at best, only an opinion. Since it explains nothing, it is useless.
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acmilan said:
I thought i should state this as many in here talk as if the theory of evolution is correct and complete, but in reality, just like God's existence, there will never be complete evidence [...] One must also remember that the theory of Evolution has its own flaws.
Claim:
Evolution has not been, and cannot be, proved.
Response:
1. There are no known serious problems with the theory of evolution. Claims that there are fall into two (overlapping) categories:
(a) Some supposed problems are questions about details about the mechanisms of evolution. There are, and always will be, unanswered details in every field of science, and evolution is no exception. Creationists take controversies about details out of context to falsely imply controversy about evolution as a whole.
(b) Some supposed problems are misunderstandings, ignorance, or fraudulent claims about what the science says.
2. Nothing in the real world can be proved with absolute certainty. However, high degrees of certainty can be reached. In the case of evolution, we have huge amounts of data from diverse fields. Extensive evidence exists in all of the following different forms [Theobald 2004]. Each new piece of evidence tests the rest.
- All life shows a fundamental unity in the mechanisms of replication, heritablility, catalysis, and metabolism.
- Common descent predicts a nested hierarchy pattern, or groups within groups. We see just such an arrangement in a unique, consistent, well-defined hierarchy, the so-called tree of life.
- Different lines of evidence give the same arrangement of the tree of life. We get essentially the same results whether we look at morphological, biochemical, or genetic traits.
- Fossil animals fit in the same tree of life. We find several cases of transitional forms in the fossil record.
- The fossils appear in a chronological order showing change consistent with common descent over hundreds of millions of years, and inconsistent with sudden creation.
- Many organisms show rudimentary, vestigial characters such as sightless eyes or wings useless for flight.
- Atavisms sometimes occur. An atavism is the reappearance of a character present in a distant ancestors but lost in the organism's immediate ancestors. We only see atavisms consistent with organisms' evolutionary histories.
- Ontogeny (embryology and developmental biology) gives information about the historical pathway of an organism's evolution. For example, whales and many snakes develop hind limbs as embryos which are reabsorbed before birth.
- The distribution of species is consistent with their evolutionary history. For example, marsupials are mostly limited to Australia, and the exceptions are explained by continental drift. Remote islands often have species groups that are highly diverse in habits and general appearance but closely related genetically. This consistency still holds when the distribution of fossil species is included.
- Evolution predicts that new structures are adapted from other structures that already exist, and thus similarity in structures should reflect evolutionary history rather than function. We see this frequently. For example, human hands, bat wings, horse legs, whale flippers, and mole forelimbs all have similar bone structure despite their different functions.
- The same principle applies on a molecular level. Humans share a large percentage of their genes, probably more than 70%, with a fruit fly or a nematode worm.
- When two organisms evolve the same function independently, different structures are often recruited. For example, wings of birds, bats, pterosaurs, and insects all have different structures. Gliding has been implemented in many additional ways. Again, this applies on a molecular level, too.
- The constraints of evolutionary history sometimes lead to suboptimal structures and functions. For example, the human throat and respiratory system make it impossible to breathe and swallow at the same time and make us susceptible to choking.
- Suboptimality appears also on the molecular level. For example, much DNA is nonfunctional.
- Some nonfunctional DNA, such as certain transposons, pseudogenes, and endogenous viruses, show a pattern of inheritance indicating common ancestry.
- Speciation has been observed.
- The day-to-day aspects of evolution -- heritable genetic change, morphological variation and change, functional change, and natural selection -- are seen to occur at rates consistent with common descent.
Furthermore, the different lines of evidence are consistent; they all point to the same big picture. For example, evidence from gene duplications in the yeast genome shows that its ability to ferment glucose evolved about 80 million years ago. Fossil evidence shows that fermentable fruits became prominent about the same time. Genetic evidence for major change around that time also occurs in fruiting plants and fruit flies. [Benner et al. 2002]
The evidence is extensive and consistent, and it points unambiguously to evolution, including common descent, change over time, and adaptation influenced by natural selection.
It would be preposterous to refer to these as anything other than facts. -
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