For years, evolutionists have hailed the chimpanzee as "our closest living
relative" and have pointed out that the DNA is 98 to 99 percent identical
between the two. Scientists now say the difference is 4 percent, double
what they have been claiming for years.
The difference between chimpanzees and humans due to single-nucleotide
substitutions averages 1.23 percent, of which 1.06 percent or less is
due to fixed divergence, and the rest being a result of polymorphism
within chimp populations and within human populations. Insertion and
deletion (indel) events account for another approximately 3 percent
difference between chimp and human sequences, but each indel typically
involves multiple nucleotides. The number of genetic changes from
indels is a fraction of the number of single-nucleotide substitutions
(roughly 5 million compared with roughly 35 million). So describing
humans and chimpanzees as 98 to 99 percent identical is entirely
appropriate (Chimpanzee Sequencing 2005).
The difference measurement depends on what you are measuring. If you
measure the number of proteins for which the entire protein is
identical in the two species, humans and chimpanzees are 29 percent
identical (Chimpanzee Sequencing 2005). If you measure nonsynonymous
base pair differences within protein coding regions, humans and chimps
are 99.75 percent identical (Chimpanzee Sequencing 2005, fig. 9).
The original 98.4
percent estimate came from DNA hybridization experiments, which
measured (indirectly, via DNA melting temperature) sequence difference
among short segments of the genomes that are similar enough to
hybridize but with repetitive elements removed (Sibley and Ahlquist
1987). Whatever measure is used, however, as long as the same
measurement is used consistently, will show that humans are more
closely related to chimpanzees (including the bonobo, sister species to
the common chimpanzee) than to any other species.
Note also, though, that evolution has not been uniform throughout the
genomes, so estimates of human-chimp divergence which consider only
part of the genome can give different results (Britten 2002, Chen et
al. 2001).
References:
Britten, Roy J. 2002. Divergence between samples of chimpanzee and
human DNA sequences is 5% counting indels. Proceedings of the National
Academy of Science USA 99: 13633-13635.
Chen, F.-C., E. J. Vallender, H. Wang, C.-S. Tzeng, and W.-H. Li.
2001. Genomic divergence between human and chimpanzee estimated from
large-scale alignments of genomic sequences.
Journal of Heredity 92(6): 481-489.
Chimpanzee Sequencing and Analysis Consortium. 2005. Initial sequence
of the chimpanzee genome and comparison with the human genome.
Nature
437: 69-87.
Sibley, C. G. and J. E. Ahlquist. 1987. DNA hybridization evidence of
hominid phylogeny: Results from an expanded data set. Journal of
Molecular Evolution 26: 99-121.
