Are Humans More Closely Related to Gorillas or to Chimpanzees?
by Amir Aslam

Are humans more closely related to gorillas or to chimpanzees? This is a question that has been asked by scientists for many years and can be answered through evolution. Evolution is one of the most powerful theories science has ever known. Evolution is a change in the gene pool of a population over a given period of time. The gene pool is the set of all genes in a species or population. One frequently used example of this change is the English moth, Biston betularia. Due to the change in the moths' habitat and the ease of which the birds were able to locate and eat the light-colored moths, a change in the coloring of the moths took place. Since their color is determined by a single gene, the change from light to dark colored genes and therefore a change in the gene pool was by definition, an evolution.

If evolution is a change in the gene pool, then what causes the gene pool to change? Several mechanisms have been discovered that change the gene pool. There are three mechanisms that add new alleles to the gene pool: mutation, recombination, and gene flow. There are two mechanisms that remove alleles: genetic drift and natural selection. With one or a combination of these mechanisms it is possible that in the proper environment, evolution may take place.

In any case, evolution is defined as a change in the gene pool. This means that evolution is a population level phenomenon. Only groups of organisms evolve. An individual organism does not evolve. So when thinking of evolution, it is necessary to view population as a collection of individuals with different traits.

All living organisms use DNA as their genetic material, with some viruses using RNA. DNA is composed of four nucleotides making a double helix. In order to compare the DNA of chimpanzees to humans and gorillas, it is necessary to understand DNA hybridization. DNA hybridization is based on nucleotide sequence similarity. This is accomplished by melting the DNA to single strands and then allowing for the strands to form double strands by slowly lowering the temperature slowly. The difference between humans and chimpanzees in the non-coding region is 1.6%. By contrast, the difference between chimpanzees and gorillas is 2.1%. These results show that chimpanzees are more similar in DNA, therefore evolutionary closer to humans. The extra-nuclear DNA or significant DNA was tested by similar methods and the difference between humans and chimpanzees proved to be 9.6%, while the difference between chimpanzees and gorillas was about 13.1%. These percentages also show that humans and chimpanzees genetically have a closer relationship. (Gibbons 376)

Table 2-1 A Comparison of the Number of Amino Acid Differences in Cytochrome c. (Margoliash, 1967)

Organism Cytochrome c (# Amino Acids Differing from Human)
Human -
Chimpanzee -
Rhesus monkey 1
Rabbit 9
Pig 10
Dog 10
Horse 12
Penguin 11
Moth 24
Yeast 38

Cytochrome c is a common protein in most higher organisms and is used as the basis of amino acid similarity, indicative of the genetic separation between the noted organisms. Cytochrome c, is a respiratory pigment found in mitochondria of eukaryotes. Cytochrome c has changed very slowly during evolution. The amino acid sequence between humans and chimpanzees are identical while between the rhesus monkey, there is a difference of one amino acid in comparison. This table shows that the amino acid sequence compared from humans are more closely related to chimpanzees.

Table 3-1 A Comparison of the Alpha and Beta Hemoglobin Chains Between Humans and Other Organisms. (Klug, 1994
Organism Alpha Chain Beta Chain
Human - -
Chimpanzees - -
Gorilla 1 1
Macaque 5 10
Mouse 19 31
Sheep 26 33
Pig 20 28
Horse 22 30
Rabbit 28 16
Chicken 45 -
Kangaroo 54 -
Carp 93 -
Lamprey 113 -

Table 3-1 is a comparison of the alpha and beta hemoglobin chains between humans and other organisms. A hemoglobin molecule is made up of four separate single chains consisting of two alpha and two beta chains and is an essential protein for the above-mentioned organisms. Hence, the single chains can be compared between species for evolutionary divergence. When analyzing the hemoglobin chains of humans, gorillas and chimpanzees, it was revealed that the differences between humans and gorillas was one amino acid in both alpha and beta chains, and there was no difference between humans and chimpanzees. The differences between gorillas and humans and the similarities between humans and chimpanzees also show that a closer genetic link exists between humans and chimpanzees.

In conclusion, in order to answer the question, "Are humans more closely related to gorillas or chimpanzees?", it is necessary to examine the results of the DNA tests and the extra-nuclear DNA tests and also examine the data from the comparisons in tables 2-1 and 3-1. These results suggest that humans are very closely related to chimpanzees and more distantly related to gorillas. Similarities in the DNA hybridization between humans and chimpanzees (9.6%) and less similar DNA hybridization between chimpanzees and gorillas (13.1%) lead to the conclusion that humans are more closely related to chimpanzees. (Gibbons, 1990) These tests prove that although twenty million years ago humans and monkeys diverged from a common ancestral form that humans have genetic links stronger to chimpanzees than those of gorillas, thus answering the question. (Klug, 1994) It is possible to see this connection through the definition of evolution. While we have progressed from the same genetic form, the change in the gene pool due to mutation, recombination, gene flow, genetic drift, and natural selection has resulted in what we now know as present day humans, chimpanzees, and gorillas.

References
Gibbons, Ann. 1990. Our Chimps Cousins Get That Much Closer. Science 250:376
Klug, William S. and Cummings, Michael R. 1994. Molecular Evolution. Concepts of Genetics 763-766
Margoliash, E. and Finch, W.M. 1967. Construction of phylogenetic trees. Science 155: 279-84