It has formerly been held that there is a 98% similarity between humans and chimps based on DNA comparisons. Many believe that more recent advances in science demonstrate an even closer relationship between man and chimp. To them and others who cite this number my advice is to throw away their old high school biology books! The 98% number hasn't been accepted by genetic scientists since 2002. Recent advances in genome sequencing have shown that humans are further removed from chimps than previously realized. In fact, the latest results in counting the DNA cytogenetic differences between us and our furry friends yields a similarity of only 95%. Refer to "Britten, R.J. 2002.’Divergence between samples of chimpanzee and human DNA sequences is 5% counting indels.' Proceedings National Academy Science 99:13633-13635" to verify the more current figures. Now, keep in mind that this number is based on the sequencing and comparison of only 1% of human and chimp genomes to date. As further comparison of the remaining 99% of the genome progresses, it is believed that the number may fall as low as 90% and is unlikely to increase beyond the current 95%.
A surprising find has arisen out of recent DNA studies. DNA sequences in chromosomes 4, 9 and 12 in the human genome are out of sequence from that of chimps. Since reordering of the DNA sequence cannot occur due to mutation, it creates a perplexing problem. How did the DNA sequences in chromosomes 4, 9, and 12 become resequenced following the evolutionary branch from chimps to humans given that progressive mutation doesn't play in? This new find challenges previously held assumptions that man descended from chimps.
To add further questions about our current understandings, more current comparisons of DNA and mitochondrial DNA (mtDNA) show that all people are so similar that scientists generally agree that there is a more recent single origin for modern humans. Previous estimates prior to 2002 held that our most recent common ancestor (or MRCA) was dated to 100,000 to 200,000 years ago, which, through regressive dating, would have placed our divergence from chimps to around 5 million years ago, ignoring the problems with chromosomes 4, 9, and 12 which suggest that we have a different origin than that of apes. However, the new studies all agree that based on mtDNA regression, "Eve" (and it is assumed "Adam" also) came on the scene as early as 10,000 years ago, not 100,000 as previously believed. [See "Heyer, E., Zietkeiwicz, E., Rochowski, A., Yotova, V., Puymirat, J., and Labuda D. 2001. ‘Phylogenetic and familial estimates of mitochondrial substitution rates: study of control region mutation in deep-rooting pedigrees.’ Am J Hum Genet 69:1113-1126."]
It remains a common misconception that recent science demonstrates a closer branching on the evolutionary path between chimps and humans with DNA similarities approaching 98.5% (to be more accurate to the older stats). However more recent science and a better understanding of the relationship of DNA, how it changes, and what constitutes meaningful change discloses some interesting problems that are forcing the science community to rethink our past. The Britten and Heyer studies I mentioned above have been collaborated by at least six other related studies. If they are correct, then there is strong evidence that humans had a more recent and sudden appearance. It also provides some answers to a perplexing problem in the human fossil record. It too shows that humans appeared more recently with no traceable human ancestors that coincide with the former 100,000 year marker.