As usual, when thinking about things to post about, I draw inspiration from various events in my life (hence the research blog post on sore throats). I had a question from a creationist today and it’s as good as any for a fairly detailed post. Here’s the quote:
Another thing, it is an important philosophical question that shapes a persons world view: where did we come from? ID answers that. Either your ancestors were slime balls that crawled out of primordal ooze, and you are just one step above monkeys who fling poo and fornicate and thats about all they do, or you are the product of a super intelligent entity which gives life a whole new meaning now doesn’t it? That’s important to some people, apparently.
After a rather amusing rebuttal (he claimed my intellect was the equivalent of a dull butter knife and I responded with “Sure looks you are the one flinging poo”), I decided that the evidence of why we think that we are very closely related to apes would be a good post. I’m sure it’s been done, but I’m nothing if not repetitive.
So, what is the evidence that we are closely related to apes?
- The human chromosome 2
- Vitamin C
- shoulder blades along the back
This list should not be taken to be everything and I may update it as I learn more. We shall see.
Human Chromosome 2
All great apes, except humans, have 24 pairs of chromosomes. Humans have only 23. Well, that’s pretty troubling if we are closely related organisms. (That’s a rhetorical statement, just so creationists can quote-mine in the future.) So, scientists came up with a testable hypothesis. If humans and great apes are closely related, then after the human lineage split from the chimpanzee lineage, there must have been an event in which two ape chromosomes combined into one human chromosome.
Fortunately, chromosomal analysis is pretty easy, once you have the chromosomes. What they found is that the human chromosome 2 is a fusion of 2 chimpanzee chromosomes. See for yourself.
As you can see, the banding pattern caused by the staining of the chromosomes matches between the human and chimpanzee.
Some additional evidence that this happened is that in the middle of the human chromosome 2, you can find telomeres. Now these normally only occur on the ends of chromosomes. In the case of human chromosome 2, we find additional telomeres right where the ends of the chimpanzee chromosomes would be.
Now look at the two ‘pinched in’ places on the chimpanzee chromosome. These are the centromeres. I won’t go into detail (link for that), but suffice to say that these centromeres are very important in the chromosomal structure. Now, note that the centromere in the human chromosome is in exactly the same place as the chimpanzee chromosome 2q. There is also a remnant of the centromere from chimpanzee 2p, in the same relative place, on the human 2.
Next up, more genetic evidence.
The Mysterious Case of the Missing Vitamin C
About 40 million years ago, a group of primates diverged from the rest of the primate group. This group all carries one mutation and they all carry the exact same mutation. The haplorrhines (known as ‘dry-nose primates’ have all lost the function of the terminal enzyme which manufactures vitamin C. Unlike all other mammals, these haplorrhines, cannot manufacture their own vitamin C and must acquire it from the environment (fruits often have large amounts of vitamin C).
Interestingly, humans have this exact same mutation. We can’t make vitamin C and we can’t make for the exact same reason that tarsiers, marmosets, spider monkeys, gibbons, gorillas and chimpanzees can’t make it.
The next is purely anatomical, but let’s take a look.
Shoulder Blades for Swinging
Most animals, indeed most monkeys, have shoulder blades on the sides of the ribcage. Their shoulder blade basically sits behind their arm. Take a look at the difference between a human and a macaque.
Now, let’s take a close look at the anatomy of a human shoulder, a chimpanzee, and what, for all intents and purposes, is a transitional fossil between the two, Australopithecus afarensis.
OK. Quick rundown. a and c are front and back views of humans (with some muscles in place on the back view). b and d are front and back views of a chimpanzee. e is a reconstruction of Homo erectus and f is a reconstruction of A. afarensis.
We are specifically looking at the similarity between the should blade structure of the chimpanzee and the human. The rest is just a red herring, so I don’t want to hear anything about ‘reconstructions’.
Notice, particularly, the shape and location of the shoulder blade, especially as compared to the macaque above. They are extraordinarily similar don’t you think. Especially considering that one of the species spends much of its time swinging from tree to tree while the other spends much time swinging from bar to bar.
Anatomical comparisons are usually very poor considerations for classification and common ancestry discussions, so I only include the one. There are many others, for example, our flexible wrist. The true measure is in genetics.
For example, a normal person would consider hippos and whales to be very closely related, yet genetically, they are very closely related. Genetic and biochemical evidence is the best for this kind of work and there are two very significant genetic characters that show the common ancestry between human and ape.
Some might be offended by this. The classic line “I ain’t no monkey” or the ever popular “My momma ain’t no monkey” are examples of this. First, humans are apes. Second, the evidence is incontrovertible, we are very, very closely related to apes, especially chimpanzees.
The sad truth is, many people would rather lie to themselves than admit something that they think is painful to them. As far as the other part of the original quote, that is our being the product of a super intelligent designer? That person just doesn’t know anything about human anatomy. The human is a very, very poorly designed organism. Maybe I’ll do a post on that later though.
4. Avarello R, Pedicini A, Caiulo A, Zuffardi O, Fraccaro M, Evidence for an ancestral alphoid domain on the long arm of human chromosome 2. Hum Genet 1992 May;89(2):247-9