"...changes in the gene pool of a population over time which result in relatively small changes to the organisms in the population — changes which would not result in the newer organisms being considered as different species." (from the atheism.about.com article mentioned at the end of this post)One case in which humans have witnessed microevolution is illustrated in a study on Biston betularia:
"In Europe there is a speckled moth called the Peppered Moth, Biston betularia. Among its members are very light-colored ones, and very dark-colored ones. Before the mid 1800s, the pale-colored ones were by far the most common kind encountered. Since they were less visible when resting on pale tree trunks, birds had a harder time seeing them, and eating them than they did the dark ones. However, then came the Industrial Revolution with its pollution, which covered tree trunks with soot making them darker. Now the dark-colored moths became the most common form because now they blended in the best with the dark, soot-covered tree trunks. In other words, with regard to the entire species, the Peppered Moth gradually evolved toward the darker form, because the darker form was better adapted for a landscape darkened with soot." (http://www.backyardnature.net/evolving.htm)To give some more examples of microevolution:
- Insects becoming immune from certain types of pesticide.
- Bacterial Resistance to Antibiotics. (see http://www.textbookofbacteriology.net/resantimicrobial.html)
- The differences seen in humans from different geographical regions.
- For more see: http://evolution.berkeley.edu/evosite/evo101/IVB1aExamples.shtml. An extremely well put together site that gives you a basic tutorial on evolutionary biology!
"Macroevolution" is used to refer to:
"changes in organisms which are significant enough that, over time, the newer organisms would be considered an entirely new species. In other words, the new organisms would be unable to mate with their ancestors, assuming we were able to bring them together." (from the atheism.about.com article mentioned at the end of this post)
Macroevolution is the part of evolutionary theory that Christians reject most often. Young Earth creationists believe in a 6,000 year old Earth (calculated from dates and ages of generation found in the Bible). The idea is that we "know" when Jesus died and we "know" his age. The list of the linage from King David to Jesus is found in the Bible along with the linage from Adam and Eve to King David. Ages of most generations are provided by the Bible, so theoretically we could calculate the age of the Earth. This number comes out to be around 4,000 B.C.E., sometime after the domestication of the dog. I wager that one can see the problem a "young Earther" may have if scientists are saying that branches of the evolutionary tree can be traced back millions of years.
Macroevolution accounts for all of the diversity of life we observe today. The evidence lays in the fossil records, DNA analysis, phylogenetic analysis, and a handful of macroevolution observances by scientists in our lifetime (even though creationists believe none exist, see http://www.talkorigins.org/faqs/faq-speciation.html#part5). All of these topics can be explored further at http://www.talkorigins.org/!
Back to John. John was trying to make the claim that he has never seen a reptile give birth to a bird, he "knows" scientists (along with the theory of evolution) say that birds come from reptiles, therefore the scientists are wrong and he doesn't believe in evolution. Many things are wrong with this argument, but let me focus on two: his claim that scientists say birds come from reptiles and he has never seen a reptile give birth to a bird.
- Scientists say birds come from reptiles.
This is a flow chart of transitional forms from reptiles to more bird-like organism. At which transitional form would you tag on the label "bird"? The distinction is obviously blurry, but at no point would you say that the reptile magically changed into a bird. This brings me to the next point:
2. I have never seen a reptile give birth to a bird.
If anyone saw this happen, this would be a strong bit of evidence against evolution because the theory of evolution doesn't actually say this. As I explained above, not only is the distinction between reptiles and birds (at their transitional phases) hard to pinpoint, the fact this process takes millions of years refutes this argument.
As I have said earlier, scientists don't see the need to differentiate between macro- and microevolution because they are guided by the same processes. You might be wondering what these processes are, so I'll conclude this post with a brief and extremely simple explanation.
An important part of evolution is that genes are heretical, thus organisms have heritable traits. The mechanism that organisms use to pass these traits to their offspring is called DNA. Mutation, the only random part of the process, can be caused by radiation, viruses, the natural DNA replication process, etc. Although most mutations have a neutral effect on the organism, some are harmful and some are beneficial. These mutations are carried over into the offspring. The organisms with the harmful mutations eventually die out (because they are less likely to breed due to death or infertility, etc.) while the organisms with the beneficial mutation (ones that help the organism in its current environment) keep breeding until the entire population has the same mutation. If enough mutations happen, then over a long period time (usually upwards of thousands of years) then entirely new species occur. Consider this example:
Let us assume that this population of circles is put into an environment where being darker in beneficial (whether the predators can see lighter prey more easily, darker circles are chosen more often by female circles as mates, darker circles can survive hotter conditions, etc.). If one or more of the circles develops a mutation that makes their body a darker shade, these darker circles are more likely to survive and therefore more likely to breed. This is where the phrase "survival of the fittest" is coined from. Over a long period of time, the entire population will be consisted of dark circles given that their environment remains constant because the darker circles will be the ones passing their traits to their offspring (one of which may have a mutation to be even darker). The incorrect side shows a misconception about evolution similar to the "reptiles give birth to birds" fallacy. Mutation do not respond to the environment; they are completely random. Therefore each circle won't spontaneously give birth to a darker circle.
For more information, I highly recommend this article: http://atheism.about.com/od/evolutionexplained/a/micro_macro.htm. The article is extremely brief and describes where the terms microevolution and macroevolution come from and how both creationists and scientists use them.
I understand that this is a lot to take in if you have little background in biology, however the information is easily available on the internet and it is explained much better than I have tried to. I am not a scientist by any stretch of the imagination, however the concepts aren't too difficult to understand even for me! If anyone out there is an evolutionary biologist or has any expertise in the field and believes I have totally misrepresented science, please leave me a comment below telling me how wrong and unintelligent I am and correct me. This way there is no way I'll mess this up again! As always, feel free to e-mail me at email@example.com to give comments, ask questions, start up a discussion, tell me what a stupid, "spawn of the devil" heathen I am that deserves to burn in hell for all eternity, or anything else you would like! I'll happily answer any e-mail! Have a great day!