There are a number of different concepts that can be used when talking about evolution. Unfortunately, many people do not stop to define the terms they are using when getting into discussions on evolution and teaching "evolution" in the classroom. Because of this, educators and parents and students can easily misunderstand one another. Below are some general terms often involved in discussions about evolutionary theory. Sorting these out can help one keep definitions straight when discussing origins and the value of "evolutionary" education in the classroom.
Change over time: The most basic definition of evolution is simply "the process of change or development over a period of time". Hence, music, cultures, sports teams all "evolve". In biology, classes of animals and plants have experienced marked change over dozens or hundreds or thousands of years. At one time, beavers were as big as today's bears, and ancient ground sloths once grew to be the size of oxen. There were once little three-toed horses and large cats with monstrous saber-like fangs. Over time, groups of animals diversify, as shown by the fossil record and common observation. This definition is extremely broad, and says nothing about what caused the change or where the beavers or sloths came from in the first place.
Descent with Modification: This term that Darwin used basically means that living creatures have the ability to create offspring like themselves, but with the potential for variation. Today, descent with modification is explained through the field of genetics and studies involving DNA, the coding mechanism of life. Through the code of DNA, creatures can produce offspring like themselves, yet with room for variation. Brown-eyed parents who have recessive gene coding for blue eyes can produce blue-eyed children. Cats can give birth to kittens with a range of characteristics, all in one litter, depending on the specific DNA coding passed on to each kitten by its mother and its father.
Adaptation: Sometimes an offspring receives certain traits or characteristics from its parents that allow it to survive in certain situations better than in others. Large-beaked finches adapt better to eating hard, large seeds, because their beaks are strong enough to crush them. Finches with long, thin beaks adapt better to getting food out of hard-to-reach places.
Survival of the Fittest: This basic concept promoted by Darwin argues that those organisms that are best able to adapt to a particular environment will live to produce more offspring. For instance, when there is plenty of food, all the finches on an island can do well. However, during times of drought, only the finches with the strongest beaks will be able to eat the hardest seeds, enabling them to survive and reproduce. If other finches with longer, thinner beaks can get seeds from places the rest of the finches can't, these will survive and reproduce. The other finches that can't compete for the food supply will die out. Soon, the "specialized" finches are reproducing more "specialized" offspring like themselves, so that obvious variations start showing up between the different groups of finches.
Natural Selection: Adaptation and Survival of the Fittest work together to create success among certain groups of creatures with certain genetic variations. "Nature" selects which ones survive based on which ones are best adapted to their environment and best able to overcome the competition. Natural Selection includes both ecological selection (overcoming competition for food, safety, shelter) and sexual selection.
Genetic Drift: This refers to the way small populations of creatures end up reproducing and passing on their genetic information and becoming specialized even if they are not the best adapted to an environment. If all the competition got killed by a lightening storm or flood or avalanche, those left behind would continue to reproduce and survive, whether or not they were the best suited to survive otherwise.
Most of the above concepts can be seen regularly in nature and are largely beyond dispute. However, the following ideas start creating heavy debate:
Speciation: This term refers to the formation of new "species" over time, generally through the mechanisms of natural selection and survival of the fittest. When many people talk about "evolution", they often mean "speciation", arguing that through natural selection, entirely new species have been formed.
Whether this can be proven actually depends on the definition of the term "species" (there is still a great deal of arguing among scientists on this subject). Usually, a species is considered to be a group that does not reproduce with other groups. Finches may become so specialized that they no longer mate with other kinds of finches. These can be considered a new "species" of finch.
Yet, evolutionists often extrapolate to argue that through these processes thousands or millions of years ago, finches evolved from some more generic form of bird, which evolved from some more generic form of vertebrate. The line should be drawn at the DNA evidence. What does the DNA allow for? How much genetic variation was originally available in the DNA of the earliest finches, and how can we determine it? Natural Selection can only work with the DNA code already present, and cannot create new DNA coding that did not previously exist. The specialized finches are still finches, and are not turning into some other kind of bird.
Mutation: To deal with this obvious problem of DNA coding, some evolutionary scientists have argued that through small mutations, new information can be added to the genetic code.
However, there is much debate over this issue. Mutations are naturally destructive and cause damage, and evolutionary scientists have been hard pressed to find "beneficial mutations". On rare occasion, a mutation can help a creature survive when it would otherwise not be able to, but only because the mutation has caused a malfunction. For instance, children with sickle-cell anemia are more resistant to malaria, but this is because their red blood cells are not functioning properly, (and large numbers still die from the sickle-cell anemia). Many "super bugs" in hospitals are immune to antibiotics -because they are actually mutated, sickly bacteria and can't function properly to take in the antibiotics. When put in competition with normal bacteria outside of a hospital setting, these "super bugs" can die off quickly.
The General Theory of Evolution: This is the popular but controversial idea that all life on earth started in a primordial soup, and that all the variation of life on earth arose through gradual evolution by way of mutation, adaptation, and survival of the fittest.
This is where the heavy argumentation over "evolution" is often focused. The general theory that all life on earth evolved from primordial microbes is based on philosophical beliefs about the nature of nature, on models, on extrapolations, and on guesswork – because it deals with theories about things that cannot be directly observed or reproduced. The best scientists can do is create models and work to fit the observable evidence to their models. In this sense, evolutionary theory is absolutely a "work in progress".
While many concepts in "evolutionary" science are useful in understanding genetics and the variations between species, it is important to recognize where observation ends, and where extrapolation and theorizing begin. Those in the information sciences recognize the vital importance of focusing on information and the genetic code, and of determining where the DNA code originated in the first place. Without a mechanism for adding information to the genetic code, natural selection and adaptation can only produce more specialized finches or dogs or horses, but they cannot tell us how finch or dog or horse DNA was programmed in the first place.
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