Human Evolution [Part I]
One of the most contentious claims of evolution is that humans are descended from an ape-like ancestor. Although Charles Darwin did not mention the subject specifically in his Origin of Species (1859), the book’s popularity added fuel to the smoldering hopes of some, and the fears of others, that naturalists would remove all barriers between man and beast. After all, if a single or few ancestral forms gave rise to every living thing, as Darwin was trying to prove, then we were no exception.
At least in the Middle Ages, people could admire the beautiful circles of Ptolemy’s astronomy, with the Earth at its very center, and assure themselves that they were the focus of God’s attention. But Copernicus, and centuries of empirical science, undermined the foundations of that comforting position. Still there was Genesis, with man so obviously the crowning glory of the creation week. Surely our art, technology, and language elevated us above the animal world. Yet Darwin allowed no separate, divine creation of man.
For all this effort to show our puny place in a thoughtless world, human evolution represents one of the most active, sensational research programs in science today. Even if our newspapers or popular magazines say nothing about a new subatomic particle, we can count on them to announce the latest tooth or bone fragment belonging to one of our alleged ancestors. Within the field itself, the issues are no less contentious. The subject of human evolution “contains more practitioners than objects for study,” quipped Stephen Jay Gould, “thus breeding a high level of aquisitiveness and territoriality” (1996, 105:16).
ENTER THE ARGUMENT
Evolution, to prove its case, must show a continuity between humans and all other life on Earth. This much, at least, has not changed since Darwin’s day. Part of this process involves teasing out similarities between man and animals, although such observations are not unique to evolutionists (Tattersall, 1995, p. 4). In 1698, English anatomist Edward Tyson noted 47 points of resemblance between men and apes. A few years later, Carolus Linnaeus, the father of our binomial classification system, included both the chimpanzee and orangutan under the name Homo troglodytes, and gave us the name, Homo sapiens. [Today, the term “hominine” refers to members of the genus Homo; “hominid” includes hominines plus our alleged ape-like ancestors; and “hominoid” includes hominids plus gibbons and the great apes (see Figure 1).]
Thomas Henry Huxley led the charge for evolutionists by publishing scientific papers and presenting public lectures on apes and men, culminating in 1863 with his Man’s Place in Nature (see sidebar, “Where Did Owen Go Wrong?”). Darwin’s massive Descent of Man created hardly a stir when it appeared in 1871, such was the pace of change in public opinion and scientific debate. Yet privately, Darwin had been contemplating a common origin for man and animals for over thirty years (Bonner and May, 1981, p. x).
FROM SIMILARITY TO GENEALOGY?
The events surrounding evolution’s rise to dominance highlight the need to address the central claim of human evolution: that there is a genealogical connection between ourselves and a creature, or creatures, with similar features. Any genealogist would appreciate the enormity of this task. Making connections among recent generations is difficult enough, without also having to find ancestors thousands of generations in the past. At least family researchers can compare similar names, although frequently these are unreliable. Even if pictorial evidence is available, physical appearance still would be a tenuous basis on which to claim inheritance in the fortunes of a suspected distant cousin. Documentary evidence, if it exists, must be studied and interpreted carefully before filling in another branch on the family tree. Evolutionists have no such documentation, although they do have access to scientific techniques that any genealogist would envy.
Imagine, for instance, being able to find similar physical features among the remains of potential relatives. This method has had some interesting applications in recent years, including an attempt to track down the final resting place of Butch Cassidy and the Sundance Kid. However, with the passing of years, it becomes increasingly difficult to assign relatedness on the basis of physical similarities.
Imagine, also, being able to compare the DNA of suspected relatives. This “DNA fingerprinting” method is very powerful because everyone has a unique sequence of DNA—except for identical twins, of course. This fact has proved very useful in all sorts of legal applications. In particular, it provides a powerful means of establishing paternity, because every child inherits half of his or her genetic code from the father.
The technique is on less-certain ground in the area of forensics. In this application, geneticists can analyze tiny samples of hair, blood, or other biological evidence left at the scene of a crime. For purely practical purposes, they analyze only small segments of DNA, and estimate the chance of finding all these sequences in an individual selected at random from a given population. Barring sloppy handling, this method can eliminate the innocent, and identify the guilty. As such, it is being used with great effect in rape cases, especially to prevent the indictment of an innocent man. As the well-publicized O.J. Simpson trial showed, however, juries can be reluctant to find a defendant guilty of murder on the basis of DNA evidence. By conservative estimates, the probability of a chance match in this case was one in a highly incriminating fifty-seven billion. Despite that mind-boggling figure, the jurors were able to find reasonable doubt in the prosecution’s case.
To take DNA fingerprinting any further is to skate on very thin ice indeed. Unfortunately, this means that our technology-hungry genealogist could not use DNA reliably beyond parent/offspring and full sibling relationships (Lewin, 1989). Only last year, a circuit court judge ruled against the exhumation of President Lincoln’s assassin, John Wilkes Booth. A great-great-grand niece and a first cousin, twice removed, wanted to know whether the grave really contained Booth’s body. The judge based his refusal in small part on the inappropriate use of DNA fingerprinting to find a match between Booth and his living, but very distant, relatives.
Genealogy based on genetics is, it seems, as limited as genealogy based on physical features. Yet these are the very techniques used by evolutionists to support their claim of a shared ape/human family tree. In the legal example just mentioned, no one is doubting that the petitioners are related to Booth, but proving this forensically is another matter. Similarly, few people doubt that all humans are related to all other humans. After all, we know that there is only one human species; that is to say, we know of no biologically, reproductively isolated human population. We know, also, that there is a fundamental reproductive barrier between chimps and humans. This is not the only way to define a species, but the distinction here is obvious.
THAT ALL IMPORTANT ONE PERCENT
The only solution left for evolutionists is to present unambiguous evidence of shared parentage. High on their list of exhibits is a 99% similarity between human and chimp DNA. At first hearing, that does not sound very ambiguous. How did they arrive at this figure, and what does it mean?
Purely for the purposes of illustration, DNA often is shown as a twisted ladder (Figure 2). Each “rung” of the ladder consists of two complementary nucleotide bases linked together by a relatively weak hydrogen bond. There are a total of four bases—adenine, thymine, guanine, and cytosine—and they are complementary in that adenine always pairs with thymine, and guanine always pairs with cytosine. The DNA in each human cell has about three billion of these rungs or base pairs. If heated to a certain temperature, the bond between the pairs will break, separating the DNA into two complementary strands. If these are mixed, and allowed to cool, the strands will rejoin. However, if the same process is applied to strands taken from two different species, the match will be less than perfect. If the mixture is heated again, the hybrid DNA will split at a lower temperature. The lowest temperature at which the split can occur is used as a guide to the similarity of the two strands (Gribbin, 1985, p. 342). When applied to humans and chimps, the technique infers a match along almost 99% of the two DNA strands.
|Figure 2. Idealized picture of DNA’s “twisted ladder.” The “rungs” consist of two pairs of complementary nucleotide bases (adenine/thymine, guanine/cytosine).|
However, this method is very crude compared with the base-by-base approach of DNA sequencing (Mereson, 1988), which is not yet complete for humans, and has barely started for chimps. Hybridization simply reflects the strength at which two strands can hold together. Large-scale sequencing, however, will decode the entire length of DNA. This approach promises to reveal every gene (i.e., those sections of DNA that encode for proteins and RNA, which is itself involved in protein production). Various methods, including hybridization experiments with human DNA and RNA, have provided a crude estimate of approximately 100,000 genes. This figure could change as closer analysis unveils more genetic secrets (Rennie, 1993; see related articles on “Cracking the Human Genome” [Part I] and [Part II]). Amazingly, these genes occupy less than 5%, and possibly as little as 2%, of the DNA strand. The remainder may serve other purposes not related directly to protein production (e.g., the prevention of copy errors; Moyzis, 1991).
The important point here is to distinguish between DNA and genes. Human and chimp DNA may be 99% the same, but that does not make our genes 99% the same, and certainly it does not make humans and chimps 99% the same. That 1% difference between human and chimp DNA grows in significance when we compare it to the 2% of human DNA dedicated to protein manufacture. Although a gross simplification, we are our genes, not our DNA. It is the proteins that provide the scaffolding of our cells and body tissues, along with the necessary chemical agents needed for life (such as enzymes and hormones). Evolution must work primarily with the genes, not the entire sequence of DNA. Of course, that 1% difference also represents thirty million base pairs. We know that this mismatch weakens hybrid DNA, but it tells us nothing about the nature of those differences. In many cases, a single out-of-place base pair can alter or cripple a gene.
At this point the evolutionists step in to point out the incredible similarities between ape and human proteins, and the genes that code for those proteins. Again, they would argue that these similarities establish a close genealogical relationship. Of course, we would expect some similarities. For example, apes and humans have hair (along with all other mammals), but how many different DNA sequences do we need to assemble the proteins of which hair is made? It is quite a different matter to create a family tree from these similarities. In fact, as anthropologist Jonathan Marks (1994) has shown, the rules of molecular evolution allow the arbitrary insertion of gaps in a gene to produce a “match” in the DNA sequence of different species (Figure 3).
Figure 3. Comparison of human and ape DNA sequences (C = cytosine, G = guanine, A = adenine, T = thymine). Arrangement 1 shows more similarity between chimps and humans (consistent with evolutionary consensus). Arrangement 2 shows more similarity between chimps and gorillas than between chimps and humans. Both arrangements attempt to find the greatest number of matches by inserting artificial gaps. The gray-lettered bases show key points of agreement.
Marks also has highlighted problems in comparing proteins. Take, for example, the well-known A, B, AB, and O blood groups, each of which represents a type of antigen (a protein-sugar “tag”) on the surface of our red blood cells. These figure prominently in everyday medical situations because types A and B are incompatible. In each case, the body’s immune system sees the other type as an unwanted intruder. More significantly, for our purposes at least, geneticists have traced the rules of inheritance for these antigens. Long before the advent of DNA fingerprinting, blood typing was used to rule out paternity or parentage (most dramatically in those classic “switched at birth” cases). As we have seen with other methods, however, the ABO system loses its reliability beyond the closest of suspected relatives. When evolutionists attempt to expand the family tree beyond humans, the system breaks down entirely (Figure 4). Of the great apes, chimpanzees have no B, gorillas have B alone, and orangutans have no O. This haphazard distribution foils any attempt to create a family tree based on ABO antigens.
|Figure 4. Distribution of ABO antigens among humans and great apes (brown text). White lines show evolutionary theory of descent, and black text shows the “random loss” of varieties. The evidence suggests four separate origins (brown boxes).|
An evolutionist could argue that most of the 1% difference occurs, not in the genes, but in noncoding regions (e.g., Gribbin, 1985 p. 343). Of course, this claim must await a complete sequencing of chimp and human DNA. Even in these noncoding regions, however, evolutionists claim similarities. For example, some stretches of DNA resemble genes, but are not used in the production of protein (at least, as far as we know). Some of these “pseudogenes” are similar from species to species, leading evolutionists to propose that they lost their function, or were accidental copies of functional genes, but were carried as stowaways on the voyage of natural selection. However, as we observed in the case of blood groups, several pseudogenes frustrate any attempt to form a clear pattern among humans and African great apes (see Bible-Science News, 1994).
Evolutionists naturally point to other protein and DNA comparisons more consistent with their expectations. Their consensus opinion places chimpanzees closer to humans than to gorillas, but nothing “in their morphology—their form and structure—offers a decisive answer, and the molecular evidence points several ways” (Andrews and Stringer, 1993, p. 225). This disagreement among methods underscores the inherent difficulty in reasoning from similarity to genealogy. In the end, we have advanced no further than Tyson’s observation in 1698 that apes and humans share certain characteristics. Darwin’s chief aim of establishing a common ancestry remains unfulfilled.
Andrews, Peter and Christopher Stringer (1993), “The Primates’ Progress,” The Book of Life, ed. Stephen Jay Gould (New York: W.W. Norton).
Bible-Science News (1994), “Do ‘Pseudogenes’ Prove a Close Human-Chimp Evolutionary Relationship?,” 32:12-13.
Bonner, John Tyler, and Robert M. May (1981), “Introduction,” The Descent of Man by Charles Darwin (Princeton, NJ: Princeton University Press).
Darwin, Charles (1859), The Origin of Species (New York: Avenel Books, 1979 reprint of the 1968 Penguin edition).
Darwin, Charles (1871), The Descent of Man, and Selection in Relation to Sex (Princeton, NJ: Princeton University Press, 1981 reprint of the 1871 edition by J. Murray, London).
Gould, Stephen Jay (1996), “Up Against a Wall,” Natural History, 105:16-18,22,70-73, July.
Gribbin, John (1985), In Search of the Double Helix (New York: Bantam Books, 1987 reprint of McGraw-Hill edition).
Huxley, Thomas H. (1864), Man’s Place in Nature (New York: D. Appleton, 1896 edition).
Lewin, Roger (1989), “Limits to DNA Fingerprinting,” Science, 243:1549-1551, March 24.
Marks, Jonathan (1994), “Blood Will Tell (Won’t It?): A Century of Molecular Discourse in Anthropological Systematics,” American Journal of Physical Anthropology. As quoted in Bible-Science News (1994), 32:12-13.
Mereson, Amy (1988), “Monkeying Around With the Relatives,” Discover, 9:26-27, March.
Moyzis, Robert K. (1991), “The Human Telomere,” Scientific American, 265(2):48-55, August.
Rennie, John (1993), “How Many Genes and Y,” Scientific American, 268(1):16-20, January.
Tattersall, Ian (1995), The Fossil Trail (Oxford: Oxford University Press).
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