Humans and chimps share 99 percent gene similarity. So goes one of the most common and seemingly convincing arguments that humans and chimpanzees arose from a common ancestor.1 The fact that chimpanzees and humans possess proteins with similar immunological properties may seem to offer further support, but the striking genetic similarity may be less striking than these particular facts suggest. Nor does genetic similarity necessarily argue for natural-process evolution.
A genome-wide comparison of humans’ and chimps’ DNA has never been made and is currently impossible. While the human genome has been sequenced, work on the chimpanzee genome has yet to begin in any real sense.2 Until a global comparison of all DNA sequences can be made, the declaration of 99 percent similarity must be considered unwarranted. Whole-genome analysis will undoubtedly identify additional similarities between the great apes and humans, but will doubtless uncover important biochemical differences, as well.
Recent separate studies by scientists from the Max Plank Institute in Germany and the University of California, San Diego (UCSD) foreshadow the anticipated discovery of these meaningful differences. These researchers found subtle but significant distinctions between the brain biochemistry of humans and that of chimpanzees.
The German group recently determined that gene expression3 in the brain tissue of humans differs markedly from that in chimpanzees and rhesus monkeys, whereas nearly identical gene expression occurs in the brain tissue of chimpanzees and rhesus monkeys.4 In contrast, gene expression in the liver and blood of chimpanzees, rhesus monkeys and humans show much similarity. According to the team’s head scientist, “Among these three tissues, it seems that the brain is really special in that humans have accelerated patterns of gene activity.”5
Scientists from UCSD identified another important difference in brain chemistry between humans and chimps. Sugars found on the surface of tissue cells vary between the two. 6-10
Chimpanzees, gorillas, orangutans and other mammals produce N-glycolylneuraminic acid (GC-neur), a sialic sugar associated with cell surfaces. Humans, however, do not produce this sugar. GC-neur serves as a binding site for certain pathogens. The absence of GC-neur makes humans immunologically distinct from great apes and other mammals.
In great apes and other mammals GC-neur is plentiful in all body tissues but occurs at its lowest levels in the brain and central nervous system. The lack of GC-neur in humans, specifically in brain tissue and its tissue distribution, signals the intriguing possibility of a relationship between the absence of GC-neur and advanced brain capacity. Experiments are underway to test this hypothesis.11
For those who view life as the work of a Creator, genetic similarity presents no problematic implications. In fact, it would be expected since humans and great apes share so many anatomical and physiological characteristics. The proteins coded by genes are the building blocks used to construct organisms. Why wouldn’t a Creator designing organisms to share physical similarities build them from similar raw materials? Biochemistry’s uniformity throughout the living realm argues against randomness and for design. It is not the building blocks (genes) themselves, but rather the amount and combination of gene products that determine differences among organisms (at least to a first approximation), as the case of chimpanzees and humans demonstrates. As more becomes known about human and chimpanzee comparative biochemistry, scientists will undoubtedly find more subtle, but significant, indicators of divine design and of designed distinctions between humans and the rest of God’s creatures.