New researches in molecular genetics have influenced many disciplines. Its application in Physical Anthropology has led to a better understanding of human evolution. And as such the pre-molecular evidence (based on physical characteristics) has been replaced by post-molecular evidence. The following discussion is related to the latter.
Immunological Techniques
During the early 1960s it was Morris Goodman who developed immunological tests to establish the close genetic relationships among humans, chimpanzees, and gorillas. The technique involved production of antisera by injecting an animal with protein (albumin) from another species. The antisera produced in this way contained antibodies of the foreign protein which was injected. The cross reaction is done between the antiserum and the immunological protein, i.e., homologous antigen. Similarly cross reaction is also done between the antiserum and the protein of other species, i.e., heterologous antigens. It was observed that greater the similarities in the immunological properties of the two species, the greater the reactions are. That is how Goodman showed that immunogically there is greater similarity between African apes and man than between Asian apes and humans.
Molecular Approach
During 1966 and 1967 Sarich and Wilson carried out more elaborate immunological experiments. The results they got supported Goodman’s findings and also enabled them to construct a molecular clock. They injected human albumin into rabbits which produced antihuman albumin. When this antihuman albumin was brought in contact with human albumin the reaction was very strong and same was the case with chimpanzee albumin, while with monkey albumin the reaction was weaker. This shows that the degree of cross reaction depends upon the number of amino acid differences between the homologous albumin (the albumin injected) and the heterologous test albumin. Sarich and Wilson thus established that closer the genetic relatedness of two species, the antigens of one will cross react with the antibody of the other antiserum.
Sarich and Wilson (1971) concluded that man, gorilla and chimpanzee last shared a common ancestor five million years ago. In their further research of 1995, they suggested that chimpanzee and man might have shared a period of common ancestry after the split of gorilla line.
Yunish and Prakash (1983) in their comparative analysis of high- resolution chromosome suggested that the taxonomic scheme of man and apes should be revised. The taxonomists’classification of two families-Hominidae for man and Pongidae for apes be changed to two subfamilies-Hominae for man and large apes and Ponginae for Orangutan. This kind of classification instead of solving the problem generated controversy. The protein-enzyme nucleic acid analysis based biomolecular evidence, showing similarities between man and African apes of Chimpanzee and Gorilla, has been found to be of primitive retentions of earlier inheritance from the common hominid stock as shown by works of Mai (1983), Kluge (1983), Schwartz (1984) and a host of others on the chromosome number and karyotyping variability.
But to suggest the revision of the taxonomic scheme of man and apes on the basis of comparative analysis of chromosome alone is a far fetched idea. It is well established fact that the family Hominidae contains single genus Homo and single species Homo sapiens. There are many characters supporting the influences of the family in the Primate order. Needless to say that “Man the tool maker” is the only culture-creating, culture-retaining, culture-transmitting creature with a complex brain and articulate speech in the animal kingdom.
DNA Hybridisation
Besides the above approaches there is DNA comparison based on hybridization technique. In this technique single stranded DNA of one species is allowed to seek out its complement in the single stranded DNA of another species. DNA strands can be separated and combined in the laboratory. When the DNA sequences of two species are similar, the bonds that develop will be stronger but when the sequences are different the bands will be weak. If the bonded pair is strong the temperature is also high. Examination of the hybrid strand shows that a double strand composed of one human and the chimpanzee strand is 97.5% fit and 2.5% amino acid sequences are different. It indicates that they have descended from a common ancestor and the minor difference in their DNA might have been due to changes since the time of their separation.
Mobile DNA Elements Approach
Mobile DNA elements are distinct DNA sequences that have remarkable ability to transport or duplicate the other regions of the genome. It has been observed that nearly 50% of the primates genome is made up of mobile repetitive DNA sequences such as Alu and LINE elements. The causes and evolutionary consequences of these mobile elements have been studied during the last decade.
Due to their distinctive mutational mechanism, these elements are exceedingly useful in constructing phylogeny particularly human-chimpanzee-gorilla trichotomy as well as that of New World Primates.
Without going into the details of the two different types of mobile DNA elements (DNA Transposons and DNA Retrotransposons), let us examine the role of Alu elements which are primate specific. Alu elements have been extensively used in primate phylogenetic studies.
Human-Chimpanzee-Gorilla Trichotomy
According to Paterson et al. (2006), the relationship among humans, chimpanzees, and gorillas have been a difficult and long standing problem. Several studies have tried to resolve this problem. Though the mtDNA studies by Horai et al. (1965) support chimpanzee as nearest living relative of humans, Satta et al. (2000) who analysed the sequences from 45 nuclear loci found that 60% of the loci support human-chimpanzee relationship. Salem et al. (2000) analysed 117 Alu Ye subfamily and 16 loci from Alu Y sub- family. They found a single most parsimonious tree with high levels of support. The resulting tree clearly clusters human and chimpanzee as a sister clad with gorilla as outgroups