In the century since he proposed it, Mr. Darwin's theory of evolution by natural selection has become nearly universally accepted by biologists, but has proven controversial among the general public. Darwin's critics raise five principle objections to teaching evolution:

1. Evolution is not solidly demonstrated.

"Evolution is just a theory,"

Darwin's critics point out, as if theory meant lack of knowledge, some kind of guess. Scientists, however, use the word theory in a very different sense than the general public does. Theories are the solid ground of science, that of which we are most certain. Few of us doubt the theory of gravity because it is "just a theory."

2. There are no fossil intermediates.

"No one ever saw a fin on the way to becoming a leg,"

critics claim, pointing to the many gaps in the fossil record in Darwin's day. Since then, however, most fossil intermediates in vertebrate evolution have indeed been found. A clear line of fossils now traces the transition between whales and hoofed mammals, between reptiles and mammals, between dinosaurs and birds, between apes and humans. The fossil evidence of evolution between major forms is compelling.

3. The intelligent design argument.

"The organs of living creatures are too complex for a random process to have producedthe existence of a clock is evidence of the existence of a clockmaker."

Biologists do not agree. The intermediates in the evolution of the mammalian ear can be seen in fossils, and many intermediate "eyes" are known in various invertebrates. These intermediate forms arose because they have valuebeing able to detect light a little is better than not being able to detect it at all. Complex structures like eyes evolved as a progression of slight improvements.

4. Evolution violates the second law of thermodynamics.

"A jumble of soda cans doesn't by itself jump neatly into a stackthings become more disorganized due to random events, not more organized."

Biologists point out that this argument ignores what the second law really says: disorder increases in a closed system, which the earth most certainly is not. Energy continually enters the biosphere from the sun, fueling life and all the processes that organize it. Just as a mother's energy "organizes" a child's otherwise messy room, so the sun through photosynthesis powers the organization of life on earth.

5. Proteins are too improbable.

"Hemoglobin has 141 amino acids. The probability that the first one would be leucine is 1/20, and that all 141 would be the ones they are by chance is (1/20)141, an impossibly rare event."

This is statistical foolishness you cannot use probability to argue backwards. The probability that a student in a classroom has a particular birthday is 1/365; arguing this way, the probability that everyone in a class of 50 would have the birthdays they do is (1/365)50, and yet there the class sits.

6. Natural selection does not imply evolution.

"No scientist has come up with an experiment where fish evolve into frogs and leap away from predators."

Is microevolution (evolution within a species) the mechanism that has produced macroevolution (evolution among species)? Most biologists that have studied the problem think so. Some kinds of animals produced by man-made selection are remarkably distinctive. If future biologists only had Chihuahuas, dachshunds, and greyhounds from the fossil record, they would surely consider them to be different species, perhaps even different genera. While all dogs are in fact the same species and can interbreed, laboratory selection experiments easily create forms that cannot interbreed and thus would in nature be considered different species. Thus production of radically different forms has indeed been observed, repeatedly. To object that evolution still does not explain really major differences, like between fish and amphibians, simply takes us back to point 2these changes take millions of years, and are seen clearly in the fossil record.

7. The irreducible complexity argument.

The intricate molecular machinery of the cell cannot be explained by evolution from simpler stages. Because each part of a complex cellular process like blood clotting is essential to the overall process, how can natural selection fashion any one part?

What's wrong with this argument is that each part of a complex molecular machine evolves as part of the system. Natural selection can act on a complex system because at every stage of its evolution the system functions. Parts that improve function are added, and, because of alter changes, become essential. The mammalian blood clotting system, for example, has evolved from much simpler systems. The core clotting system evolved at the dawn of the vertebrates 600 million years ago, and is found today in lampreys, the most primitive fish. One hundred million years later, as vertebrates evolved, proteins were added to the clotting system making it sensitive to substances released from damaged tissues and so greatly increasing its sensitivity. Fifty million years later a third component was added, triggering clotting by contact with the jagged surfaces produced by injury. At each stage as the clotting system evolved to become more complex, its overall performance came to depend on the added elements. Mammalian clotting, which utilizes all three pathways, no longer functions if any one of them is disabled. Blood clotting has become "irreducibly complex"as the result of Darwinian evolution.

Darwin's theory of evolution has proven controversial among the general public, although the commonly raised objections are without scientific merit.

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