|
|||||||||||||||||||||||||||||||||||||||||||
Under the Scope
Five Proofs of Evolution -
In this article, we look at five simple examples which support the Theory of Evolution.
The Probability of Life -
Creationists have long asserted that the chances of life forming naturally are so remote that they could not have happened. Read about how, in fact, the chances are much wider than most think.
Featured Videos
What Is The Evidence of Evolution -
A short but well-presented, simple explanation of the various lines of evidence for Evolution
Latest FAQ AdditionsExternal LinksResources Support Ads |
ScienceEvolution is simply stated as change over time. Languages, societies, and knowledge all have the ability to evolve. In Biology, evolution refers to the change of genetic traits over time.
Natural Selection is one of the mechanisms which drives evolution. It is popularly characterized as "survival of the fittest," though that is not always the most accurate description. It is the tendency for life forms which are best suited to their environments to have a better chance to reproduce than those that are not. For example, in a cold environment, an animal with lots of fur is more likely to reproduce than a bald animal, since the bald animals will die more quickly.
Evolution is often criticized by opponents as being "just a theory." This argument is especially common in America, where the word "theory" usually means an unproven idea. However, in science a theory is the highest degree of certainty. Gravity is "just a theory." The Earth orbiting the Sun is "just a theory." By definition, a scientific theory is a hypothesis which has withstood rigorous testing and is well-supported by the facts. There is overwhelming evidence for biological evolution, just as there is overwhelming evidence for gravity.
This is an issue which often confuses the general public, as the two words, theory and law, have very different common meanings. But in science, their meanings are very similar. A theory is an explanation which is backed by "a considerable body of evidence," while a law is a set of regularities expressed in a "mathematical statement." This is why Newton's Laws of Motion are referred to as laws and not theories. They are expressed with simple equations (like f = ma for his 2nd Law of Motion). Evolution, and most of Biology, cannot be expressed in a concise mathematical equation, so it is referred to as a theory. A scientific law is not "better" or "more accurate" than a scientific theory. A law explains what will happen under certain circumstances, while a theory explains how it happens.
Yes. Evolution has been observed both in the laboratory (diseases adapting to become resistant to drugs) and in nature (new species of flowers, mice, insects, etc. developing). While it is true that new traits can appear through the accumulation of small random genetic mutations, it is the non-random process of Natural Selection that determines which traits to keep and which to discard. For example, a random mutation may cause a brown squirrel to be born white. But if the squirrel lives on a brown tree, its color will quickly alert predators to its existence. The white squirrel will not live long enough to reproduce and pass on the trait. In this environment, nature selects for brown squirrels, not white. If the process were random, then the white squirrel would survive just as well as the brown. While it is true that many mutations can cause problems for an organism, sometimes lethal, not all mutations are harmful. Most mutations are caused by single-point errors in the copying of a strand of DNA. For example, a strand of ATAGC may change to ATATC. This can have three major effects: a deleterious effect, a positive effect, or no effect at all. Deleterious effects, those which threaten the survival of the organism, will not accumulate, because they will kill the organism before it has a chance to reproduce. Conversely, mutations which cause no effect or a positive effect will accumulate in a population's genome. This is how Natural Selection works. It "selects" for positive changes in the genome, because only the positive changes will accumulate. Certain mutations can add new, large pieces of DNA at a time. See this question on Gene Duplication for more information.
This is accomplished through a process called Gene Duplication, which is believed to play a major role in Evolution. Because of a mistake during meiosis, an organism may end up with two copies of the same gene. After this happens, the usual mechanisms of point mutation and natural selection can evolve one of the copies into coding for something completely new, while retaining the original gene. To test how quickly gene duplication can occur, an experiment was performed on yeast in 1998. After only 450 generations, it was discovered that the "hexose transport" genes had duplicated several times. As of the time of this writing, no, scientists have never created cellular life in a laboratory from scratch. The technology simply does not yet exist to manipulate molecules with the precision required to create all of the inner workings of a cell, built one atom at a time. However, many of the important building blocks of life have indeed been created in a laboratory, including amino acids, self-replicating RNA molecules, and self-sealing and self-replicating lipid bubbles (ie, cell membranes) which are profound steps toward the goal of one day creating fully-synthetic life. Transitional fossils bridge gaps between two species. Due to the difficulties in creating fossils in the first place, and the fact that speciation sometimes occurs very quickly in small groups, transitional fossils can be rare in the fossil record. However, even given these circumstances, there are still thousands of transitional fossils known to science, including those illustrating the evolution of modern fish, the transition of fish to amphibians, amphibians to reptiles, reptiles to birds, reptiles to mammals, and the evolution of human beings (as well as many other species). Please see this video for great examples of transitional fossils: http://www.evolutionfaq.com/vi Also, see this Wikipedia page detailing just a partial list of transitional fossil examples: http://en.wikipedia.org/wiki/L The concept of a "missing link" between humans and apes arose in the 19th century, when the fossil record was largely incomplete. Large gaps separated species, casting doubt on the theory of evolution. But in the last 130 years, a plethora of fossils have been discovered, greatly narrowing the gaps between species. The Australopithecus afarensis fossil known as "Lucy" is considered to be a key fossil bridging the gap between humans and primitive hominids.
Radiocarbon dating is just one of many "radiometric" dating techniques. While contamination in the laboratory might happen on rare occasions, radiometric dating remains a trusted and reliable method of determining the age of a sample. The technique relies on the constant rate of decay of certain radioactive elements in the sample. For example, rubidium-strontium dating relies on the decay of rubidium-87 to strontium-87. Rubidium-87 has a half-life of 50 million years (the amount of time for half its mass to decay into strontium). Using this figure, scientists measure the amount of rubidium and strontium in a sample to determine its age.
The second law states that "In a closed system (one in which energy cannot enter), Entropy will not decrease." Since Entropy often refers to disorder, this law is often taken to mean that order cannot arise from disorder. How then would life, which is highly ordered, form naturally? The answer, simply, is that life is not a closed system. Energy is constantly being added to the Earth from the Sun, which fuels the plants, which in turn fuel other life. This is how plants, for example, can have more energy than the seeds they originally sprouted from. But life is not the only example of order from disorder. Snowflakes, crystals, lightning, and sand dunes are all examples of non-living matter organizing into complex structures.
While there is no direct fossil evidence for the evolution of DNA (because of its size and fragility), scientists have theorized on its origins based on verified laboratory evidence. One theory goes like this: RNA, the compliment molecule to DNA, was the first to evolve naturally from materials already common in the pre-biotic Earth. Self-replication was achieved through catalytic actions in RNA-based molecules, called ribosomes, or possibly through an intermediary molecule. This step still remains unverified to science as of this writing. Once self-replication had been achieved, the forces of Natural Selection took over. For example, those molecules which were protected from the elements survived longer and reproduced more. So, any molecules which found themselves with a lipid bubble (which also forms naturally) would have a better chance of reproducing. After many incremental steps, the lipid bubbles eventually became cell membranes, and the molecules DNA. For more information on the probability of life forming this way, please see this article. |
||||||||||||||||||||||||||||||||||||||||||