Arguing on a Website - Explaining Evolution
I didn't write much on the blog this week because I spent a few lunch breaks getting caught up in a discussion in the comments section of an article in the local paper. So, I'll do what I often do in these situations, and copy my comments here. It's a bit repetitious of other things I've written before, but due too the nature of comments, a bit briefer.
You should read the Letter to the Editor that kicked off the conversation first. Be warned that much of the discussion in the comments section degraded into name calling, triggered by the second letter at that link.
Here's my first comment.
Although I agree with much of the sentiment of Jim Edwards, I did see a few places where what he wrote is in need of correction, or where I might add a litte more information.
"First of all man did not evolve from apes."
Granted, this is a semantic issue, but it's one of my pet peeves. Humans did not evolve from any of the other extant apes, true. We didn't evolve from chimps or bonobos (they didn't evolve from us, either). We all three species share a common ancestor. Further back still, we share a common ancestor with gorillas, and even further back with orangutans. But if you were to get in a time machine and travel back to any of those common ancestors, whatever species they might be, they would still be referred to as apes. It would be like arguing that crows didn't evolve from birds, but only share a common ancestor with birds.
Regarding the time of the split, the current best estimate is around 6 million years between us and chimps & bonobos. The other apes split off from our lineage earlier than that. You have to go back around 20 million years for the split between old world monkeys and us apes, and back around 30 million years for the split with new world monkeys.
If you're really interested in the family tree, just google "primate phylogeny".
Regarding 'missing links', I'm not sure what people expect them to look like, but there are plenty of transitional fossils that have been found. To give just two examples, tiktaalik roseae is a great example of the transition from fish to tetrapods, and ambulocetus is a great example of the transition from terrestrial mammal to whale. But keep in mind that these examples don't rest solely on their own. You have to look at them in context of other fossils. For example, animals like Eustheopteron and Panderichthys are similar to Tiktaalik, but more fish like, while animals like Acanthostega and Ichtyostega are also similar, but more tetrapod like. On the human side, just google "talk origins hominid skulls", and you'll find a page showing skulls grading gradually from earlier hominid ancestors into us modern humans.
And my second:
"I have no doubt that the DNA of apes and humans are similar. I wouldn't be surprised if doves and pigeons have similar DNA. They resemble each other. It doesn't prove they came from the same ancestor."
Why would our DNA be so very similar to that of a chimp's if not for common ancestry? Let me use an example. Most animals can make their own vitamin C. They don't need to eat foods high in the vitamin because their bodies simply synthesize it from the other molecules of the food they eat. Scientists have found the gene responsible for this, the L-gulano-γ-lactone oxidase gene. They've found a broken copy of this gene in humans. So the first question is, why would we have a broken copy of a gene, unless we inherited it from an ancestor with a functioning copy? Now, I know some creationists might say that maybe Adam and Eve did have functioning copies of this gene, and mutation crippled it. But guess what, scientists have also found this gene in chimps, macaques, and other primates, and it's broken in the same location as the human copy. So now you have to accept that this gene either just happened to mutate in the same location in all of these different animals, or that a creator intentionally put the same broken, non-functioning gene in all these animals, when it just makes so much more sense to assume that it mutated in a common ancestor of all these animals, which passed it on to all of its descendants.
(As to why a broken gene could have persisted in successful animals, if you're eating a diet rich in fruits and vegetables, it really won't hurt you if you can't make Vitamin C, so there's no selection pressure for those individuals with a working copy vs those with a broken copy.)
And L-gulano-γ-lactone oxidase isn't the only example. We share other pseudogenes with the great apes, and similarities in 'junk' DNA also match the pattern predicted by common ancestry.
And then my third and final comment:
in response to tdgriffin:So, I take it you disagree with me? Oh well. But I still wonder why we, in our never ending quest for the perfect species, would hang onto a broken copy of an unnecessary gene over millions of years, since we and the apes decided to go our separate ways. When I break a cd, I chunk that bugger.
Another thing I wonder about, when I hear it mentioned: Just how many generations would it take for a black family living in New York to become white, or a white family living in South Africa to become black?
Natural selection only acts on beneficial or harmful traits. Beneficial traits allow an organism to have more offspring, so that trait becomes more common in a population. Harmful traits cause an organism to have less offspring, so that trait becomes less common in the population. Neutral traits aren't acted on by natural selection, and can persist (although, in the long run, neutral traits tend to deteriorate or drift just because there's no pressure from natural selection to maintain them). Also keep in mind, that there's no mechanism in our cells to do what you propose - cut out bad sections of DNA. Our cells just copy the DNA, making a few mistakes here and there in mutations. And of course, there's no conscious intent. You can't will your cells to cut out your broken L-gulano-γ-lactone oxidase gene in the sperm or eggs that you'll provide to your children.
So, some of our distant ancestors lived in an environment where they ate lots of fruit and vegetables, and got plenty of Vitamin C from their diet. When some mutation occurred that crippled Vitamin C synthesis, it didn't help or hurt that individual. Even if a mechanism existed to do it, cutting out the broken gene wouldn't have been noticeably beneficial. It was a neutral mutation. So, it didn't hurt that individual's chances of having offspring, and the broken gene began to spread.
But now there is an interesting question - if the broken gene wasn't beneficial, how did it become so widespread as to become fixed in the entire population? Here's where it's good to remember that populations are composed of individuals, and that sometimes a little bit of chance comes into play. From time to time, there will be population bottlenecks. This may be due to hard times that kill off most of a population, or from a small group becoming isolated and then developing into a new species. So when you get down to those small population sizes, chance plays a big role in which versions of genes are present and, and consequently which will persist in that population. (You can read more about this on Wikipedia under 'Founder Effect': http://en.wikipedia.org/wiki/Founder_Effect
As to the question of skin color, I honestly don't know, but I suspect that in modern times, it might not happen at all. Remember that in evolutionary terms, 'fitness' merely means successfully leaving offspring. And for natural selection to act on a trait, it has to result in individuals having either more or less children than other individuals with different traits. In modern day New York City or modern day South Africa, where much of people's lives are spent indoors, and where dietary supplements are readily available for those with Vitamin D deficiencies, I doubt there's any strong selection pressure on skin pigment.