Greater Than 98% Chimp/Human DNA Similarity? Not Any More ...

Greater Than 98% Chimp/Human DNA Similarity? Not Any More.
Originally published in Journal of Creation 17, no 1 (April 2003): 8-10.
Abstract
A new report in the Proceedings of the National Academy of Sciences suggests that the common value of >98% similarity of DNA between chimp and humans is incorrect.
A new report in the Proceedings of the National Academy of Sciences suggests
that the common value of >98% similarity of DNA between chimp and humans
is incorrect.1 Roy Britten, author of the study, puts the figure
at about 95% when insertions and deletions are included. Importantly, there
is much more to these studies than people realize.
The >98.5% similarity has been misleading because it depends on what is
being compared. There are a number of significant differences that are difficult
to quantify. A review by Gagneux and Varki2 described a list of
genetic differences between humans and the great apes. The differences include
‘cytogenetic differences, differences in the type and number of repetitive
genomic DNA and transposable elements, abundance and distribution of endogenous
retroviruses, the presence and extent of allelic polymorphisms, specific gene
inactivation events, gene sequence differences, gene duplications, single
nucleotide polymorphisms, gene expression differences, and messenger RNA splicing
variations.’3
Specific examples of these differences include:
Humans have 23 pairs of chromosomes while chimpanzees have 24. Evolutionary
scientists believe that one of the human chromosomes has been formed through
the fusion of two small chromosomes in the chimp instead of an intrinsic
difference resulting from a separate creation.
At the end of each chromosome is a string of repeating DNA sequences called
a telomere. Chimpanzees and other apes have about 23 kilobases (a kilobase
is 1,000 base pairs of DNA) of repeats. Humans are unique among primates
with much shorter telomeres only 10 kilobases long.4
While 18 pairs of chromosomes are ‘virtually identical’, chromosomes 4,
9 and 12 show evidence of being ‘remodeled.’5 In other words,
the genes and markers on these chromosomes are not in the same order in
the human and chimpanzee. Instead of ‘being remodeled’ as the evolutionists
suggest, these could, logically, also be intrinsic differences because of
a separate creation.
The Y chromosome in particular is of a different size and has many markers
that do not line up between the human and chimpanzee.6
Scientists have prepared a human-chimpanzee comparative clone map of chromosome
21 in particular. They observed ‘large, non-random regions of difference
between the two genomes.’ They found a number of regions that ‘might correspond
to insertions that are specific to the human lineage.’7
These types of differences are not generally included in calculations of
percent DNA similarity.
In one of the most extensive studies comparing human and
chimp DNA,8 the researchers compared >19.8 million bases.
While this sounds like a lot, it still represents slightly less than 1%
of the genome. They calculated a mean identity of 98.77% or 1.23% differences.
However, this, like other studies only considered substitutions and did
not take insertions or deletions into account as the new study by Britten
did. A nucleotide substitution is a mutation where one base (A, G, C,
or T) is replaced with another. An insertion or deletion (indel) is found
where there are nucleotides missing when two sequences are compared.
A
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Substitution
Insertion/deletion
Figure 1. Comparison between a base
substitution and an insertion/deletion. Two DNA sequences can be compared.
If there is a difference in the nucleotides (an A instead of a G) this
is a substitution. In contrast, if there is a nucleotide base which is
missing it is considered an insertion/deletion. It is assumed that a
nucleotide has been inserted into one of the sequences or one has been
deleted from the other. It is often too difficult to determine whether
the difference is a result of an insertion or a deletion and thus it is
called an ‘indel’. Indels can be of virtually any length.
The Britten9 study looked at 779 kilobase pairs to carefully examine
differences between chimpanzees and humans. He found that 1.4% of the bases
had been substituted, which was in agreement with previous studies (98.6%
similarity). However, he found a much larger number of indels. Most of these
were only 1 to 4 nucleotides in length, although there were a few that were
> 1000 base pairs long. Surprisingly, the indels added an additional 3.4
% of base pairs that were different.
While previous studies have focused on base substitutions, they have missed
perhaps the greatest contribution to the genetic differences between chimps
and humans. Missing nucleotides from one or the other appear to account for
more than twice the number of substituted nucleotides. Although the number
of substitutions is about ten times higher than the number of indels, the
number of nucleotides involved in indels is greater. These indels were reported
to be equally represented in the chimp and human sequences. Therefore, the
insertions or deletions were not occurring only in the chimp or only in the
human and could also be interpreted as intrinsic differences.
Will evolution be called into question now that the similarity of chimpanzee
and human DNA has been reduced from >98.5% to ~95%? Probably not. Regardless
of whether the similarity was reduced even below 90%, evolutionists would
still believe that humans and apes shared a common ancestor. Moreover, using
percentages hides an important fact. If 5% of the DNA is different, this
amounts to 150,000,000 DNA base pairs that are different between them!
A number of studies have demonstrated a remarkable similarity
in the nuclear DNA and mtDNA among modern humans. In fact, the DNA sequences
for all people are so similar that scientists generally conclude that
there is a ‘recent single origin for modern humans, with general replacement
of archaic populations.’10 To be fair, the estimates for a
date of a ‘most recent common ancestor’ (MRCA) by evolutionists has this
‘recent single origin’ about 100,000-200,000 years ago, which is not recent
by creationist standards. These estimates have been based on comparisons
with chimpanzees and the assumption of a chimp/human common ancestor approximately
5 million years ago. In contrast, studies that have used pedigrees or
generational mtDNA comparisons11,12,13have yielded a much
more recent MRCA—even 6,500 years!14
Research on observable generational mutation events leads to a more recent
common ancestor for humans than phylogenetic estimates that assume a relationship
with chimpanzees. Mutational hotspots are believed to account for this difference.15
However, in both cases, they are relying on uniformitarian principles—that
rates measured in the present can be used to extrapolate the timing of events
in the distant past.
The above examples demonstrate that the conclusions of scientific investigations
can be different depending on how the study is done. Humans and chimps can
have 95% or >98.5% similar DNA depending on which nucleotides are counted
and which are excluded. Modern humans can have a single recent ancestor <10,000
or 100,000-200,000 years ago depending on whether a relationship with chimpanzees
is assumed and which types of mutations are considered.