Uniquely Human

By Ann Gauger

You’ve probably all heard the statement somewhere that we are 98-99% identical in our DNA sequence to chimps. Although the number has been revised downward as more detailed comparisons are made, a recent estimate still says we are 96% identical [1]. We also have significant similarity to gorillas and to orangutans [2]. 

When we look at the level of physiology, anatomy, reproduction, cognitive capacity, and behavior, though, we are much more different from great apes than these DNA comparisons might suggest. There are numerous traits that distinguish us from great apes, though that is not what the popular science articles emphasize. Care to guess how many?

Would you believe hundreds? In 2005 a partial list of traits that distinguish us from great apes was published [1].  I won’t list them here, but I would like to point out that the differences are not minor. Many of them raise questions about the suitability of great apes as models for human disease. Our organ physiology, biochemistry, and endocrinology are different. Our susceptibility to diseases such as AIDs, malaria, hepatitis B/C and influenza A are different. Our neurobiology is different, not only in brain size, but in density of neurons and synapses. Our reproduction and development are different. For example, human infants require extended care after birth. This is in part because infant brains are still growing rapidly and forming new synapses, then remodeling connections as they learn. Even adult humans can grow new neurons. Most significantly, though, our behavior, cognitive capacity, communication, social organization and culture are radically different from great apes—81 differences listed for these categories alone.

Can Darwinian natural selection account for all this? I have my doubts, for reasons to be discussed.  

1. Varki A, Altheide TK (2005) Comparing the human and chimpanzee genomes: Searching for needles in a haystack. Genome Res. 15:1746-1758.

2. Hobolth A, Dutheil JY, Hawks J et al. (2011) Incomplete lineage sorting patterns among human, chimpanzee, and orangutan suggest recent orangutan speciation and widespread selection. Genome Res. 21: 349-356.