The Human Genome Revealed

The Human Genome Revealed

Feb. 12, 2001


The human genome is about to be published, and it has 30,000 to 40,000 genes, compared to 13,600 for the fruit fly. This is much less than the initial estimates of 80,000 to 100,000 genes. The small flowering plant Arabidopsis thaliana has about 25,000 genes. Only about 1.5 percent of the human genome appears to consist of genes, which code for proteins. In addition, it is known that the genes tend to cluster in small regions of the human genome, with large amounts of non-coding DNA in between. Furthermore, humans differ little from each other in their DNA.

What is the significance of these findings for the creation-evolution discussion? First, the comparision with a fruit fly can be misleading. Size does not necessarily correlate with complexity. A fruit fly is actually a complex organism, with a nervous system, a digestive system, a muscular system, eyes, legs, and a kind of external skeleton. In addition, a fruit fly has wings and antennae, which humans do not have. Also, the 13,600 genes of a fruit fly code not only for its organs and structure but also for the basic biology of its cells, which is similar to that of all cells. So 13,600 genes code for a tremendous amount of biological complexity. In addition to all of this complexity, humans have probably over 16,000 more genes! This is enough to code for a tremendous amount of complexity. Perhaps it is surprising that humans have so many more genes than the fruit fly.

Each protein is really a chemical machine that can interact in more than one way and can change its shape depending on its interactions to promote or hinder further reactions. Each gene can actually code for more than one protein; the cell can make certain stretches of DNA contribute to the synthesis or not depending on other substances present in the cell. So a given gene can produce a number of variations of the same chemical machine, as conditions may require. In addition to the proteins, the cells contain other substances (such as bases, ATP, etc.) that are synthesized by the proteins and interact with them. Furthermore, the DNA itself is highly complex and interacts with the proteins. Therefore one can have a high degree of complexity from a small number of proteins.

What about the Arabidopsis? Plants need a highly complex system to create proteins from carbon dioxide, water, nitrogen, light, and trace elements. Animals can get their nutrition mostly ready made from plants, so they can be much simpler. In addition, plants are immobile, and cannot rely on motion to protect themselves. Therefore they need chemical defenses to protect themselves, and this requires more genes. So again, it is not surprising that humans have only a few more genes than the Arabidopsis.

These findings also add a new twist to the DNA similarity between humans and chimpanzees, estimated to be about 98.5 percent. Even if all of the human genes were different from those of a chimpanzee, the DNA could still be 98.5 percent similar if the noncoding DNA of humans and chimpanzees was identical. Of course, human and chimpanzee genes probably are similar, but the degree of similarity cannot be estimated from the overall DNA similarity.

Why is so much of the human DNA non-coding? Perhaps it has some functionality that we do not know. It is also possible that this non-coding DNA provides a place for harmful chemicals to bind and cause damage there rather than damaging the precious genes. This excess DNA may therefore reduce the number of harmful mutations.

The smaller number of genes does make it easier to imagine apes and humans having a common ancestor 5 or 10 million years ago, since the smaller genome can tolerate a higher mutation rate without error catastrophe. But the number of genes may still be too large.

If the number of genes really turns out to be about 30,000, then this can be a testament to the marvelous design of life. Only a genius could create us with so few genes performing so many functions.

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