In early 2001, when the first draft of the human genome sequence was released by the National Institute of Health and Celera Genomics, the moment was heralded rightly as a new dawn for modern medicine. The sequencing effort revealed that we humans have approximately 30,000 genes interspersed within our DNA, as well as countless other regions that regulate whether these genes are turned on or off.
Knowing the nature of these genes, which are used to build the human body, and the manner in which they are regulated will most certainly lead to a better understanding of human disease. Using the human genome sequence, doctors may one day be able to diagnosis patients long before symptoms become evident and then treat these patients with individualized medications, thereby reducing possible side effects. Medical researchers may be able to develop drugs that are more potent and more specific, and they may be able to do so in shorter periods of time.
While such possibilities rightly continue to give researchers much cause for excitement, there is another reason that the completion of the human genome has been so celebrated in the scientific community, and it has nothing to do with medicine. Working under the media radar for decades, evolutionary biologists have been busy exploring pieces of the human genome in a concerted effort to discover exactly how humans may have evolved from other animals. Having the entire genome sequence at their disposal has proven to be a boon to their efforts. Researchers can now compare the entire set of genes that humans possess with other animals, such as flies and mice, which also have had their genomes sequenced. The hope is that such efforts may shed light on how things such as the human immune system or the human brain are built from our limited number of genetic building blocks.
While comparing human genes with those of mice and flies has certainly been instructive at some levels, evolutionary biologists have been patiently holding their collective breath for the arrival of the chimpanzee sequence. The reason the sequence has been awaited with such anticipation is that evolutionary biologists widely believe it holds the key to understanding the genetics of what makes humans human.
Physiologically and genetically, humans share more similarities with chimpanzees than with any other living species. In fact, evolutionary biologists believe that chimps and humans split from a common ancestor a mere 5 million years ago, which is the geological equivalent of an eye blink. Since genes are known to change very slowly, the question evolutionary biologists have been faced with is this: How did humans acquire the changes necessary to become such a unique species in a mere 5 million years?
One way scientists have attempted to resolve this dilemma is to suggest that there really is no difference between humans and chimps. In other words, humans are merely hairless chimps who like to drive cars and build cathedrals. While such a position goes against common sense, it was supported by the oft-repeated mantra that chimps and humans are 99% identical at the level of DNA. In fact, it was hoped that once the chimp sequence was completed, researchers could decipher that handful of genes that would unlock the “minor” differences between chimps and their more social cousins. However, with the recent release of the complete sequence of chimp chromosome 22, all hopes of such an easy resolution have been dashed.
Chimp chromosome 22 is analogous to our human chromosome 21. When researchers lined up these two chromosomes, they found that the sequences were 98.5% identical. This number is a bit misleading, though, because there were quite a few places where the sequences didn’t line up properly; either the chimp chromosome had some DNA the human chromosome lacked or vice versa. Such gaps were found a staggering 68,000 times along the chromosome.
Further complicating the picture is the number of genes that have significant variation between the two species. Of the 231 genes on human chromosome 21, at least 47 (more than 25%) show significant difference with their chimpanzee counterparts. So much for easily locating the few minor variations. The reality is that chimps and humans have a great deal of variation at the level of the DNA — much more than most researchers expected.
One might be tempted to ask why researchers wanted things to be simpler, why many academics hoped for much more continuity between chimps and humans when our everyday experience argues against this simplistic view. The answer lies in a desire to remove the line that separates humans from the rest of the animal world, thereby reducing humans to mere material beings.
Way back in the 1950s, Theodosius Dobzhansky, one of the preeminent evolutionary biologists of the 20th century, stated that if man descended from chimps in a purely naturalistic manner, this represented “a reaffirmation of man’s dignity and liberation from spiritual bondage.” Naturalistic evolution is the modern-day apple of the Garden of Eden. Sink your teeth into its fruits, and be liberated from God. Eat it, and you then can decide what is right and wrong.
You can construct a world in which morality is pliable, semi-disposable and utterly convenient. In such a world, concern about our salvation becomes foolish, and attempts to live in accordance with the Judeo-Christian moral code are nothing more than a pathology in need of correction. Such is the “liberation” that Dobzhansky speaks of, and having seen the effects on society, one cannot help but wonder if it is time to put back on the “chains.”
Sharing sequence similarities with chimps is but one in a long line of characteristics we share with the rest of the animal kingdom. This should not be surprising in the least, as we are animals, after all — albeit ones in a unique relationship with our creator. Despite this, it gives many academics a seemingly perverse joy to point out these similarities, one by one, as if this mounting evidence somehow undermines our unique place in the animal kingdom and thereby nullifies our moral and theological dimension. Undermining this is only possible, though, if one simultaneously ignores the elephant standing in the corner — the obvious chasm that separates us from chimps.
Only humans have codified language to the extent that we write poetry, make laws and debate abstract ideas. Only humans act as true teachers, shaping and modifying the behavior of our young. Only humans are born with an innate moral sense of what is right and wrong. Only humans cry at weddings; in fact, only humans have weddings, and only humans have, no matter how disfigured it becomes, a longing for the infinite.
Although there is much in common, our DNA exhibits significant differences with that of chimps. Such results are compatible with the commonsensical view that humans and chimps are profoundly different. It takes a Ph.D. to see it otherwise. Keep this in mind the next time someone comments that we are merely hairless chimps because we share 98% of our DNA. Tell them you’ll take their argument seriously the next time you see a chimp discussing the character development in Moby Dick.
Daniel Kuebler, Ph.D., is an
assistant professor of biology at
of Steubenville, Ohio.
- February 13-19, 2005