The idea that human beings and chimps have
close to 100% similarity in their DNA seems to be common knowledge. The figures
quoted vary: 97%, 98%, or even 99%, depending on just who is telling the story.
What is the basis for these claims and do the data mean there really is not much
difference between chimps and people? Are we just highly evolved apes? The
following concepts will assist with a proper understanding of this issue:
Similarity (“homology”) is not an absolute indication of common ancestry
(Evolution) but certainly points to a common designer (creation). Think about a
Porsche and Volkswagen “beetle” car. They both have air-cooled, flat,
horizontally-opposed, 4-cylinder engines in the rear, independent suspension,
two doors, boot (trunk) in the front, and many other similarities
('homologies'). Why do these two very different cars have so many similarities?
Because they had the same designer! Whether similarity is morphological
(appearance), or biochemical, is of no consequence to the lack of logic in this
argument for evolution.
If humans were entirely different from all other living things, or indeed if
every living thing was entirely different, would this reveal the Creator to us?
No! We would logically think that there must be many creators rather than one.
The unity of the creation is testimony to the One True God who made it all
(Romans 1:20).
If humans were entirely different from all other living things, how would we
then live? If we are to eat food to provide nutrients and energy to live, what
would we eat if every other organism on earth were fundamentally different
biochemically? How could we digest them and how could we use the amino acids,
sugars, etc., if they were different from the ones we have in our bodies?
Biochemical similarity is necessary for us to have food!
We know that DNA in cells contains much of the information necessary for the
development of an organism. In other words, if two organisms look similar, we
would expect there to be some similarity also in their DNA. The DNA of a cow and
a whale, two mammals, should be more alike than the DNA of a cow and a
bacterium. If it were not so, then the whole idea of DNA being the information
carrier in living things would have to be questioned. Likewise, humans and apes
have a lot of morphological similarities, so we would expect there would be
similarities in their DNA. Of all the animals, chimps are most like humans[1],
so we would expect that their DNA would be most like human DNA.
Certain biochemical capacities are common to all living things, so there is even
a degree of similarity between the DNA of yeast, for example, and that of
humans. Because human cells can do many of the things that yeast can do, we
share similarities in the DNA sequences that code for the enzymes that do the
same jobs in both types of cells. Some of the sequences, for example, those that
code for the MHC (Major Histocompatibility Complex) proteins, are almost
identical.
What of the 97% (or 98% or 99%!) similarity claimed between humans and chimps?
The figures published do not mean quite what is claimed in the popular
publications (and even some respectable science journals). DNA contains its
information in the sequence of four chemical compounds known as nucleotides,
abbreviated C,G,A,T. Groups of three of these at a time are “read” by complex
translation machinery in the cell to determine the sequence of 20 different
types of amino acids to be incorporated into proteins. The human DNA has at
least 3,000,000,000 nucleotides in sequence. A proper comparison has not been
made. Chimp DNA has not been fully sequenced.
Where did the “97% similarity” come from then? It was inferred from a fairly
crude technique called DNA hybridization where small parts of human DNA are
split into single strands and allowed to re-form double strands (duplex) with
chimp DNA [2]. However, there are various reasons why DNA does or does not
hybridize, only one of which is degree of similarity (homology) [3].
Consequently, this somewhat arbitrary figure is not used by those working in
molecular homology (other parameters, derived from the shape of the “melting”
curve, are used). Why has the 97% figure been popularized then? One can only
guess that it served the purpose of evolutionary indoctrination of the
scientifically illiterate.
Interestingly, the original papers did not contain the basic data and the reader
had to accept the interpretation of the data “on faith.” Sarich et al. [4]
obtained the original data and used them in their discussion of which parameters
should be used in homology studies [5]. Sarich discovered considerable
sloppiness in Sibley and Ahlquist's generation of their data as well as their
statistical analysis. Upon inspecting the data, I discovered that, even if
everything else was above criticism, the 97% figure came from making a very
basic statistical error - averaging two figures without taking into account
differences in the number of observations contributing to each figure. When a
proper mean is calculated it is 96.2%, not 97%. However, there is no true
replication in the data, so no confidence can be attached to the figures
published by Sibley and Ahlquist.
What if human and chimp DNA was even 96% homologous? What would that mean? Would
it mean that humans could have 'evolved' from a common ancestor with chimps? Not
at all! The amount of information in the 3 billion base pairs in the DNA in
every human cell has been estimated to be equivalent to that in 1,000 books of
encyclopedia size [6]. If humans were 'only' 4% different this still amounts to
120 million base pairs, equivalent to approximately 12 million words, or 40
large books of information. This is surely an impossible barrier for mutations
(random changes) to cross. [7]
Does a high degree of similarity mean that two DNA sequences have the same
meaning or function? No, not necessarily. Compare the following sentences:
There are many scientists today who question the evolutionary paradigm and its
atheistic philosophical implications.
There are not many scientists today who question the evolutionary paradigm and
its atheistic philosophical implications.
These sentences have 97% homology and yet have almost opposite meanings! There
is a strong analogy here to the way in which large DNA sequences can be turned
on or off by relatively small control sequences.
The DNA similarity data does NOT quite mean what the evolutionary popularizers
claim!
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NOTES AND REFERENCES
1. However, Jeffrey Swartz, an evolutionary anthropologist at the University of
Pittsburg, maintains that man is closer to orangutans in gross morphology. Acts
and Facts, 16 (5):5, 1987.
2. Sibley and Ahlquist, 1987, J. Molec. Evol. 26:99-121). The resulting hybrid
duplex material is then separated from single-strand DNA remaining and heated in
2 to 3 degree increments from 55o to 95o C, and the amount of DNA separating at
each temperature is measured and totaled, comparing it to human-human DNA
re-formed as duplex. If 90% of the human DNA is recovered with heating from the
human-chimp hybrid, compared to the human-human DNA, then there is said to be
90% normalized percentage hybridization.
3. Sarich et al. 1989. Cladistics 5:3-32.
4. Ibid.
5. Molecular homology studies could be quite useful to creationists in
determining what were the original created 'kinds' and what has happened since
to generate new species within each kind. For example, the varieties / species
of finch on the Galapagos Islands obviously derived from an original small
number that made it to the islands. Recombination of the genes in the original
migrants and natural selection could account for the varieties of finch on the
islands today - just as all the breeds of dogs in the world today were
artificially bred from an original wild dog/wolf kind not long ago. It is
interesting that molecular homology studies have been most consistent when
applied within what are probably biblical kinds and contradict the major
predictions of evolution regarding the relationships between the major groups
such as phyla and classes (see ref. [6] regarding the latter).
6. Michael Denton, 1985. Evolution: Theory in Crisis. (Burnett Books, London).
7. Haldane's Dilemma recognizes the problem for evolutionists of getting genetic
changes in higher organisms, especially those which have long generation times.
Due to the cost of substitution (death of the unfit) of one gene for another in
a population, it would take over 7x1011 years of human-like generations to
substitute the 120 million base pairs. Or in 10 million years (twice the time
since the chimp/human common ancestor is alleged to have lived), only 1667
substitutions could occur, or 0.001% of the difference. There has simply been
insufficient time for ape-like creatures to turn into humans. And this
understates the problem by assuming perfect efficiency of natural selection and
ignoring deleterious processes like inbreeding and genetic drift, as well as
problems posed by pleiotropy (one gene controlling more than one characteristic)
and polygeny (more than one gene controlling one characteristic) - most real
genes. See W.J. ReMine, The Biotic Message (St. Paul Science, St. Paul,
Minnesota, 1993), pp. 215-217.