Friday, November 19, 2010

99% Chimp... but also 35% Daffodil?

"In the context of a 35% similarity to a daffodil, the 99.44% of the DNA of human to chimp doesn’t seem so remarkable. After all, humans are obviously a heck of a lot more similar to chimpanzees than to daffodils. More than that, to say that humans are over one-third daffodil is more ludicrous than profound. There are hardly any comparisons you can make to a daffodil in which humans are 33% similar." ~ Dr. Jonathan MarksWhat it Means to be 95% Chimpanzee: Apes, People, and their Genes

You have probably heard it before, "Humans are 99% chimp!" The percentage number of genetic similarity reported ranges from 90-99% (the actual number is probably closer to 90% when one takes into account indels--insertions and deletions in the DNA sequences--but that is not really important for our purposes here). This statement is based on work done by Mary-Claire King and A. C. Wilson in 1975. Their work showed several human and chimpanzee proteins display a 99% agreement in amino acid sequence. This indicated that humans and chimpanzees are closer genetic relatives than anyone at that time had thought. Soon popular evolutionary news caught wind of this and the field has never been the same since. It seems like compelling evidence for an Darwinian paradigm. Is it?

Not really, actually. As Dr. Marks states above, we could also say that humans are 35% daffodil based on this method of comparison, which is absurd. Comparisons based on the percent similarity of genetic sequences is basically meaningless. It being meaningless has led others, like Science correspondent Jon Cohen, to write, "Now it’s totally clear that it’s [the 99% genetic similarity] more a hindrance for understanding than a help." Most of the scientific community that supports naturalistic evolution has largely abandoned this comparison since it has no value. Yet, this icon of evolution is still floating around in popular media and text books.

Why does this comparison have little value? Well, let me try to explain it using an example. Assume that you and I each have a box of colored pencils. Each of our boxes contains 100 pencils. When we compare the boxes we find that 99 of our colors are the same and we each have one color the other does not have. If we each start to draw are we going to come up with pictures that are 99% similar? No, of course not. Why? Because the pictures depend not so much on the colored pencils we use but on the way we express ourselves in our drawings, how the colored pencils are used functionally. We may be using the same supplies but we would use them in vastly different ways. Well, genes are like that. Genetic similarity in organisms counts for nothing, it is how the genes are expressed that really matters. Having similar genes means nothing because functionally they operate very differently in different organisms.

Recent work on the FOXP2 gene creates a great example of this. (This is going to get a little technical but I think it is very helpful in illustrating my point above with an important, real-life example.) This gene has gotten a lot of attention lately because of its importance to language capability. This gene codes for a DNA-binding protein, which are proteins used in differential gene regulation--the controlling of activity in genes much like a volume control. They can turn genes "on" or "off" or regulate their activeness anywhere in between. The FOXP2 gene plays this role in humans and other organisms, like chimpanzees.

In humans this gene is critical for language capability. A study done by the Max Plank Institute (published in Nature in 2001) showed that any modification of this gene in humans cripples language capability. It not only disables the ability of the humans to make the sounds necessary for language but it also disables their ability to comprehend language completely. In this study they also looked at the amino acids that make up the protein that this gene produces--the FOXP2 protein--in chimps, mice, and humans. Out of the 715 amino acids that make up the protein in chimps, mice, and humans, the mouse and human protein differed by only three amino acids and the chimp human protein differed by only two amino acids (that is about a 0.3% difference).

In a recent paper also published in Nature, a team of scientists from several universities reported on an analysis they did of how this difference in the FOXP2 gene for humans and chimps affected biological development. In order to study the effect they culture two sets of neurons that had the FOXP2 gene removed from them. (They did this so they could have the same starting point for each gene they were studying.) In one set they introduced the human FOXP2 gene and in another set they introduced the chimp FOXP2 gene. They then observed how the neurons were affected by the different genes. What they found was profound. In the set of neurons with the human gene there were 60 other genes that were up-regulated (more active) by this protein compared to the chimp neurons and there were 50 other genes that were down-regulated (less active) by this protein compared to the chimp neurons. So, the introduction of one human gene that is 99.7% similar to the chimp version of the gene had a profound affect on 110 other genes in development! A two-out-of-715 amino acid difference had significant biological consequences.

This study illustrates how a 90-99% genetic similarity between humans and chimps really means nothing. Even if one were to grant that the similarity is 99% (as I briefly mentioned above, the number is closer to 90%), that 1% genetic difference has profound implications when it comes to gene expression in each species. Gene similarity is meaningless. Gene expression is what is important.

By His Grace,

4 comments: said...

Seems to me that this argument would be unnecessary if we interpret the two creation stories in genesis as parables. That is sort of necessary, because they conflict on the order of creation. God is certainly able to set in motion an evolutionary process which leads to man. God would certainly understand the complexities of the developing universe without any difficulty. However, explaining to the Israelites the scientific details would merely have bewildered them. the important point was that their ancestor, Abraham, had been chosen by the all-powerful Diety Who created the universe.

A. Taylor Rollo... said...

Thanks for the comment, though I am not really sure how it follows from this article. The problem here is not one with Ge. 1-2 but simply pointing out that something treated as an icon of evolution is actually a meaningless comparison. It cannot be cited as proof for a Darwinian paradigm because it does not, in fact, prove anything of value.

But, that being said, interpreting Ge. 1-2 as parables does not work. They are not written in the style of Hebrew parables but are written as Hebrew historical narrative. It is also not necessary to interpret them that way because they do not actual conflict. They are not two creation stories and the text does not present them that way. Ge. 1:1-2:3 presents God's big-picture perspective on creation, and then Ge. 2:4ff narrows in on the sixth day to give us the details about the creation of Adam, the Garden, and Eve. And, considering that those details are the ones that are important for the story of the fall in Ge. 3, it makes perfect sense that God would go from big-picture view to narrowing in on His creation of man the Garden to give us more details there.

Finally, your point about the Israelites not needing to know every detail is certainly true and valid. However, saying that God does not give them every detail about certainly does not mean that God does not give them any details about creation. Ge. 1-2, Ps. 104, and a whole host of other creation passages give us details that we take into account when interpreting the details that we gather from nature.

Alchemist said...

You can make it even simpler than that. Twins are essentially clones, thus 100% the same genetically. I've never met a set of twins that were exactly the same. Also wasn't there a cat that was cloned and the parent and daughter had completely different coat patterns?

Also point mutation. One base pair gets changed = cystic fibrosis, or death... So yeah. It's perfectly evident that % conservation of genes is completely meaningless.

The take-home message is that journalist aren't very concerned with accuracy and people are too lazy to fact check. There are a bunch of blatantly false thing that get accepted as dogma, because a journalist miss-quoted a scientist and the general public latched on to it.

A. Taylor Rollo... said...

Thanks for your comment, Alchemist. Those are other good points about twins and mutations.

Also, I completely agree with journalists and media. Whenever I presented a paper at a conference and saw journalists on the front row, I cringed because I knew they would either misunderstand or misquote me 90% of the time. Fortunately, my research was not interesting enough for much hype anyway. :)