Every subject in the intellectual sphere has its great tropes. Statistics, quotes, even legends and myths that have achieved widespread notoriety throughout the field and have entered into the world of common sense and public knowledge. This sort of knowledge also becomes especially difficult to challenge because it begins to form a sort of foundation of thought upon which all other facts and figures must concur with. If you need help identifying claims like this, just listen for the familiar refrain of, “everyone knows that…”, or, “the concensus is clear that…” when, in reality, very few truths are so obvious.
The world of science is certainly no exception to this trend and the fields of biology, origin-of-life research, anthropology, evolution, and human origins are rife with such claims. We’ve discussed this a bit in regards to evolution beforebut there are many more. A particularly familiar one is that of genetic similarity between chimpanzees and modern humans. Anyone who has studied evolutionary biology or anthropology probably recalls the familiar figure that humans and chimpanzees share something like a 98-99% genetic similarity. Another widely known fact revolves around what is known as “chromosome 2” and that it represents proof of common descent among chimps/great apes and humans.
To the uninitiated, these sorts of claims are almost impossible to engage with or defeat in discussion and, as with other similar truth claims of “mythical” proportion, can lead many into doubting any worldview that might object to those claims. But where do these claims come from? What is their history? How are we to understand them? Are they truly accurate? And is there any reason to doubt their provenance?
Where Do Human-Chimpanzee Similarity Claims Come From?
Given that the field of modern genetics originates less than a hundred years ago, fully kicking in with Watson and Crick in the early 1950’s, the specific claims of genetic similarity are rather young, historically speaking. That is not to say that one cannot make some general observations based on obvious morphological (physical characteristic) similarities. Carolus Linnaeus, whom you may recall as the father of modern taxonomy from science class, grouped apes and humans into a similar category as primates. And Darwin himself is also noted as having made similar observations regarding the features and presumed evolutionary history of the great apes and mankind.
But with the advent of the genetic revolution, scientists sought to study these similarities in a much more quantitative, some might say “scientific” or objective, way. These sorts of comparisons began in earnest in the ’70’s and ’80’s using amino acid/protein comparisons and staining techniques. You may have done similar experiments in school where a dna sample is stained to produce chromosome banding that can be used to identify unique genetic patterns.
One such notable experiment that gave rise to the modern claims of genetic similarity between chimpanzees and humans comes from Mary-Claire King. She was one of the first to perform and publish amino acid sequence experimental results showing on order of 99% percent genetic similarity. But comparing a small sample set of proteins, while promising, was nothing compared to more direct comparisons of dna sequences and chromosomes. These experiments began in earnest in the 1980’s with banding experiments. In those tests, the banding patterns for human and chimp chromosomes were virtually identical.
There were, however, some notable differences. For instance, a number of human chromosomes contained an inversion, or the reversal of a certain segment of DNA within the chromosome. As well, telomeric and centromeric DNA, non-coding structures used to assist in proper cell replication, appeared in different amounts. But the most notable difference was discovered in comparing the chromosome counts between the species. Chimpanzees possess two pairs of 24 genes for a total of 48 while humans possess two pairs of 23 genes totaling 46.
This discrepancy could possibly be explained in that human chromosome 2 appeared to actually be the result of a fusion of two chimpanzee chromosomes placed end-to-end. If this similarity indeed resulted from a fusion of previously separate chromosomes, this would have resulted in one less chromosome per pair, thus reducing the total by two and explaining the difference in counts. As well, the structural DNA features, such as the centromere and telomere sequences, appeared to be consistent with what one would expect were a fusion of two chromosomes to have occurred. This supposed fusion has provided a very compelling example for evolutionists in their claim that humans are indeed descended from a common ancestor with chimpanzees.
Since then, with the advent of more sophisticated DNA sequencing and comparative techniques, scientists have been able to use other means to test genetic similarity in, hopefully, increasingly accurate ways. With technology available into the mid-1980’s and 90’s, direct gene-to-gene comparisons were possible. In 2003, Morris Goodman and colleagues conducted a comparison of 97 genes via 90,000 base pairs (aka the familar A/C/T/G pairs that make up DNA) and found a 98.4-99.4 percent similarity. Additionally, studies have also been done comparing noncoding DNA between chimps and humans. This is presumed to be especially valuable because noncoding DNA does not code for proteins and therefore does not directly influence functional characteristics. Because of this, it is thought to be less susceptible to natural selective changes. A comparison of one such sequence, the beta-globin gene cluster, showed a similarity on the order of 98.4 percent.
As you can see, the results between many different DNA comparisons over time has shown a remarkable consistency. In a world where many scientific disciplines have seen wild changes and recalibrations with technological improvements, the relative stability of chimp-human comparison results are a welcome departure. But while this data may look very promising to an evolutionary paradigm, are there problems with these methodologies? Are there comparison considerations that have been overlooked? And is it indeed most fitting to look at these results as firm evidence in favor of the evolutionary worldview?
Is Genetic Similarity Even A Problem?
One valid point to raise for the Christian is that the Bible actually does expect and predict some degree of genetic similarity to begin with. In Genesis passages that mention the creation of mankind, such as Genesis 1:26 and 5:1, the Hebrew verbs used are telling. The verbs used for “make” and “create”, in the Hebrew, “asa” and “bara”, connote slightly different actions. Asa connotes the use of existing material, or that which has already been created, in the formation of mankind. On the other hand, bara connotes the creation of something entirely new which has never before existed.
So, in a very real way, the Biblical text itself, even at a cursory glance, expects if not predicts a degree of genetic similarity between mankind and other animals. With this in mind, percentages of genetic similarity between humans and great apes that are often used to demean the concept of Biblical special creation should be met with both a healthy skepticism toward future results and a hearty acceptance when it comes to similarities proper.
What About the Differences?
With the advent of more full genome sequences of humans and chimpanzees and the technology available to more directly compare those full sequences, differences have begun to creep in that were not previously detected.
In 2002, the International Consortium for the Sequencing of Chimpanzee Chromosome 22 (who comes up with these names, right?) conducted one of the first studies including a genome-to-genome comparison. DNA fragments from chimps that were able to be directly compared to human sequences continued to show a 98.77 percent similarity. However, around 15,000 of the 65,000 fragments did not align with any human sequence at all, representing apparently unique genetic segments. A subsequent study by the Max Planck Institute showed only a two-thirds match between chimp and human sequence alignment. What we see in these studies is that, of DNA segments that are able to be directly compared, the traditional 98-99 percent similarity indeed exists. But these numbers do not represent full similarity across the genome.
When unique segments are compared, segments that represent insertions and/or deletions (referred to as indels by geneticists), a different number is reached. Studies taking into account insertions, deletions, and substitutions have rendered results ranging from 95 percent to 86.7 percent and many others have noted instances where chromosomal comparisons identified tens of thousands of these indel differences. As well, comparing mitochondrial DNA in this way (which you may recall mentioned in our overview of genetics relating to Adam and Eve) showed a 91.1 percent similarity, not 98-99 percent.
How Much Does Genetic Similarity Even Matter?
But in a very real sense, should genetic similarity be one of the main measures that are looked to for evolutionary proof and does that sort of comparison bear out? On the other side of the coin, now that other species have had their genomes mapped and studied and now that genetic comparisons are far easier and quicker to do, we know, for instance, that humans and daffodils share a rather large degree of genetic similarity, something like 35 percent. Genetic similarity is even higher in mice, where common genes between humans and mice bear around 99 percent similarity. In a very humorous moment, anthropologist Jonathan Marks remarks,
“In the context of a 35% similarity to a daffodil, the 99.44% of the DNA of human to chimp doesn’t seem so remarkable. After all, humans are obviously a heck of a lot more similar to chimpanzees than to daffodils. More than that, to say that humans are over one-third daffodil is more ludicrous than profound. There are hardly any comparisons you can make to a daffodil in which humans are 33% similar.”
So it is becoming more clear that genetic comparison figures like 98-99 percent similarity between chimpanzees and humans, in light of more recent evidence, are no longer accurate. Nor are they nearly as powerful given the marked genetic similarity between humans and other species with even greater obvious, morphological differences.
What About Other Differences?
As well, with this increased focus and study of genetic similarities, studies have also been done that shed light on several small yet marked and important differences and these differences, despite their relative size, represent far more sizable challenges to the concept of common descent.
One such example is that of a cell-surface sugar called N-glycolyl-neuraminic acid, or “GL-neur” (thank God for abbreviations). GL-neur is found widely in mammals, including chimpanzees, but is absent in humans. This absence has been described as having many benefits for humans and could explain quite a bit regarding differences in human immunological and brain development. But how this absence came about, especially within an evolutionary paradigm, is problematic. Put simply, the sort of DNA sequence replacement or loss that is postulated to have taken place is in the vast number of cases catastrophic to an organism. And the important role that cell-surface sugars play in general exascerbates that problem since any change in the nature or presence of those sugars and the DNA that codes them would normally represent a loss of function and would hence be destructive or fatal. So, if such a change were to be derived from the normal natural selection process, such a change, having happened in a “just right” way, against all normal odds, should elicit a skeptical reaction for the scientist.
Another influential example is that of the FOXP2 gene, also known as the language gene. Obviously, one of the most notable differences between humans and the great apes, as well as all other mammals, is that of the faculty of language. The FOXP2 gene actually has many functions within the body from aiding the development of a number of organ systems especially including brain functions related to human language. FOXP2 defects severely affect language ability, and not only the ability to speak but also the ability to actually understand grammar or speech sounds themselves. Because of this key role, it is believed to be very resistant to to mutations and natural selection pressure. So it is quite interesting that there exists a very small difference, only two amino acids difference within the FOXP2 protein between humans and the great apes. And yet, this subtle difference seems to account for a huge difference in language capability and development. As in the GL-neur case, the sort of “just right” circumstances must be at play within the evolutionary paradigm, not only that mutations occurred at the right time and in the right way, but that, at the same time, no other mutations occurred that rendered the population less fit.
And What About That Chromosome 2?
As mentioned earlier, the supposed fusion of human chromosome 2 has also long been tauted as a simple yet compelling example of open-and-shut evidence for common descent. However, despite its ubiquiteness among the annals of evolutionary evidences, there are a number of reasons why this explanation falls a bit flat.
For one, chromosomes are seemingly engineered to prevent just this sort of fusion. During a breakage, chromosomes are said to have what are called “sticky ends”. These ends act kind of like magnets that attract to other broken chromosome pieces but are also resistant to fusion with intact chromosomes. Indeed, the telomeric structures of the chromosome are meant to actively prevent this from occurring. So, in order for such a fusion to have occurred, it would have required a series of increasingly rare events, such as some sort of telomeric fusion or a “just right” fusion of chromosomes that themselves had broken in a “just right” way. As well, not only would the organism’s DNA need to have been mutated thusly, but the sex gametes as well. The reproductive process has its own safeguards to preventing reproduction between organisms with different chromosome counts, ranging from nonviable offspring to infertility.
As well, the evidence for fusion due to genetic similarity is also less compelling than is often communicated. For instance, Cornelius Hunter notes that “the repetitive telomere sequence is far too short and too dissimilar to indicate a fusion event. Furthermore the supposed fusion region is full of genes with the supposed fusion site lying within a highly expressed RNA gene.” Additionally, the mere existence of a fused pair of chromosomes does not explicitly imply any descendant relationship. As Hunter also notes, “such a fusion event would have occurred in, and spread through, an early human population. There is no evolutionary relationship revealed. Even if evolution is true, this fusion event would give us no evidence for it. The fused chromosome did not arise from another species, it was not inherited from a human-chimp common ancestor, or any other purported common ancestor.”
The Bottom Line
If you are still alive after this lengthy discussion containing scientific jargon, let us recap what lessons we have learned. We have learned that genetic similarity between chimpanzees and humans is indeed real and present but that this similarity is not foreign to or in opposition with scripture for the Christian. We have also learned that such similarities can be very much overplayed and selected in such a way as to emphasize the similar at the expense of the dissimilar. That the differences between chimps and humans, while sometimes small, can represent far greater relative significance. And we’ve learned that chromosome 2 fusion, while a popular theory, has some fatal flaws that must be reconciled before any sort of evolutionary conclusion can be drawn.
Hopefully this information has expanded your brain and intrigued you to learn from and converse with those who favor evolutionary arguments with less fear and trepidation. But for now, you deserve a break, so I invite you to use your advanced human characteristics to make yourself a sandwich.