PerspectivesAre you interested in submitting a Perspective Article? Be sure to read The Science Advisory Board's Editorial Guides for Perspective Articles. Click here. Deadly Microbes Turned Some Apes into Humans by Sergey N. Rumyantsev, M.D., Ph.D., DSc The routine study of human evolution has mainly investigated the remains of prehistoric bones (beginning with the first insect eating mammals) and tools (mainly focusing on the final stages of anthropogenesis). This approach discovered some macroscopic evolutionary changes of the skeleton (directly) as well as the brain and muscles (indirectly). However, it could not uncover the intimate moving forces of the process which starts at the molecular level [1]. The investigation presented here, in a very short form, was devoted to trying to fill this gap in knowledge. The research was based on the discovery of relicts of the evolution preceding the inherent immune features of modern humans, and on the assessment of infectious (molecular) selections’ creative influence on different stages of human descent. The evolution of the earliest insect-eating mammals to the descent of the apes (the Tropical forest stage of primate evolution) and then the descent of Homo genus (the Savannah stage of primate evolution) has been traced. Long before the beginning of anthropogenesis, in the Late Cretaceous epoch, i.e. from near 99.6 million to 65.8 million years ago (mya), the tropical angiosperm forests began to spread across the Earth, following a period of global warming. During this epoch, which lasted 33.8 my, some small, insect-eating mammals climbed into the trees, presumably in search of pollen-distributing flying insects (bees, butterflies), as well as ants, termites, their eggs, larvae and corpses. These insects provided the mammals with proteins, carbohydrates, vitamins and minerals. This kind of foraging provided them with the capacity for both intensive self-reproduction and gradual accumulation of random mutations. However, the tropical forest was not a relatively easy place for insect-eating mammals to find and catch food of animal origin. Forces of natural selection (predators, poisonous plants and some infections) preformed a slow transformation on some of the earliest mammals into primitive forms of herbivorous primates. The next stage of human evolution, the descent of the apes, lasted from the beginning of the Tertiary period (from around 65 mya up to 5.3 mya), to the Palaeocene Epoch, when tropical forests had spread over all the continents. The descendants of some insect-eaters came to rely on edible plant parts from the forest, and this change set the stage for the initial emergence of herbivorous primates. As plant foods assumed increasing importance, selection gradually gave rise to the suite of traits which facilitated movement and foraging in trees [2]. Although the proper, and diverse tropical food provided apes with the capacity for both intensive self-reproduction and gradual accumulation of mutations, the rate and intensity of their evolution was restricted by the sluggishness of the selective agents’ multistage action that existed at the time. The lengthy process continued for four or five epochs of the Tertiary period, lasting until about 59.7 my. The selective power of the life-threatening challenges which existed at this time (predators, poisonous plants, insects and infections transmitted by insects) were too weak and slow to perform rapid evolutionary changes on the given human predecessors, and push them toward their next developmental stage. The food of vegetarian origin could not serve as a source of infectious agents dangerous for animal plant eaters [3]. The foraging for vegetative growth generously provided tropical inhabitants with sources of vital energy for intensive self-reproduction. Millions of generations of apes had changed during this long period of primate evolution. Different vegetarian apes began to emerge. Over 100 species of herbivorous apes, including the predecessors of modern chimps, gorillas and Macaques emerged at the end of Miocene, which lasted from 23.8 to 5.3 million years before the present. Among these vegetarian species only one, the predecessor of Australopithecus, was constitutionally prepared to be considered the most probable ancestor of future hominids. The acknowledged ape ancestor of Humankind, Australopithecus, evolved in the tropical forests more than 4.5 million years ago at the beginning of the Pliocene. The Pliocene was the final epoch of the Tertiary period that lasted around 3.5 my, from 5.3 million to 1.8 million years before the present. The descent, worldwide spread and subsequent extinction of Australopithecus lasted 2.7 my (between 4.5 mya and 1.8 mya). Like modern chimpanzees, monkeys and prosimians as well as many apes contemporary to it, Australopithecus was a small-bodied, small-brained bipedal vegetarian hominid. While its brain was not appreciably larger than that of apes today, it was well adapted to find food products provided by tropical plants, and thus obtained adequate nutrition with a certain amount of energy, vitamins and amino acids. All apes of this range actually obtain an estimated 94 percent of their annual diet from plants, primarily ripe leaves and fruits, and supplemented it with insects [2]. Thus like modern chimps, gorillas and Macaques, the members of Australopithecus genus were, in fact, not absolute vegetarians. For instance, today’s macaques are omnivorous, primarily eating roots, herbs, fruits and leaves, occasionally supplemented by some insects and invertebrates [4]. Toward the end of Pliocene, the final epoch of the Tertiary period (5.3 mya), the climate of the Earth changed dramatically. The global cooling dried out tropical woodlands, and as a result, the tropical forests shrank and were replaced by savannah grasslands. The existing primates (over 100 species of herbivorous apes) lost their forest homes and had to adapt to the expanding grasslands. These shifts transformed both the flora and fauna in the relevant geographical areas. Both the gradual and abrupt changes in climate induced sharp transformations of environmental selective conditions for all primate species, including the earliest member of the human family, Australopithecus. The majority of vegetarian apes appeared to be unable to survive in these new conditions. The fauna of the Earth lost 90% of its vegetarian apes within this period of time. Meanwhile, the predecessors of modern chimps, gorillas and Macaques, which probably inhabited the remains of previous tropical areas, avoided the worst influences of global cooling, as well as the subsequent selection holocaust induced by the savannah environment. The primates in the expanding savannah areas must have faced very hard dietary challenges. New ecological conditions forced them to eat whatever was at hand. Instead of the plethora of moist tropical products, the Pliocene hominids had the choice of eating either dry grass, which provided little energy for the former tropical feeders, or the bodies of hunted and dead animals that were extraordinary rich both in easily digested forms of proteins and carbohydrates, as well as in vitamins and minerals. Thus, the former fruit eaters were forced to become the predators and the consumers of carrion. Extraordinary importance of the meat-eating for human evolution has been accentuated by numerous anthropologists [5, 6] It has been stated that evolutionary adaptation of few human ancestors to the food of animal origin has been followed by substantial both physiological and anatomical transformations of all parts of alimentary system [6]. Like the meat-eating diet, the starch diet is also considered an important evolutionary force for humans. It could possibly have supported the growth in hominin brains [7] that occurred some 1.8 million years ago. The data of recent investigations continues to confirm the paradigm. According to the study of fossil records, the consumption of more animal foods with early human ancestors was likely important for its further evolutionary transformation in the genus Homo sapiens [8]. But neither the analysis of anatomical physiological features of both humans and modern primates nor the discovery of fossil records has revealed the intimate moving forces of this process. Besides, one may suppose that in the processes of the bio-molecular evolution there acts regulations similar to the correlation rule [9], according to which any evolutionary change of one organ entails a change in all other organs connected to it. Molecular components of any body as well as its organs are closely connected, both anatomically and functionally. That is why the descent of a new version of a molecule must inevitably entail the conjugated transformations of other molecules. These secondary changes also play a part in the fitness of organisms, thus additionally improving the efficiency of natural selection and subsequent evolutionary transformations of organelles, cells, tissues, organs and entire bodies [1]. It is especially important to note that in comparison to the foregoing stages, the Savannah stage of anthropogenesis was exceptionally short. It included three very important events: the disappearance of 90% of the ape species that had evolved during the tropical stage; the descent, worldwide spread and subsequent extinction of Australopithecus during 2.7 my (between 4.5 mya and 1.8 mya); and finally, the descent of Homo genus (between 1.8 mya 0.1 mya). The Savannah stage took 5.3 million years i.e. it was 11 times shorter then the foregoing descent of apes (59.7 my). What is more, the proprietary descent of Homo genus took nearly 1.8 my i.e. was 35 times shorter than the evolution of its primate predecessors (63.2 my). The rapid tempo of human evolution resulted in the formation of a countless number of unique features, different from the nearest primate relatives. Such very fast and extraordinarily productive evolution was reached by uncompromisingly cruel, but highly intensive, molecular selection. It was predetermined by the forced transition from a herbivorous to a carnivorous diet at the beginning of the Savannah stage. New ways of foraging provided them not only with the best food, but also with a wide range of possibilities for catching various life-threatening infections and for the abrupt intensification of natural selection. The proper quantity and quality of selective agents was provided by repeated epidemics induced by food of animal origin inseminated with deadly microbes. The few survivors reached life-saving victory by being descendants of mutant individuals whose molecular constitution provided them and their offspring with constitutionally inherent immunities to specific infections. Later human migrations substantially expanded both the circle and the quality of microbe species that human predecessors encountered on their way. The subsequent genetic admixture of distinct human populations further increased the number of new protective features of the human molecular constitution, since many thousands of human generations had been subjected to selective infectious pressures. As a result, many traces of foregoing infectious induction of anthropogenesis are now found in the constitutional attributes of modern people [10]. Most of our contemporaries reveal properties of inherent immunity against anthrax, smallpox, botulism, typhus, influenza, meningococcal infection, tuberculosis, etc [11-14]. The discovery of inherent immunity against infectious microbes in anthropogenesis opens a new window on both the evolution of humankind, and the interpretation of modern epidemics. Its results provide a new perspective upon both the molecular timing of the preceding evolution of Homo sapiens, and the evolutionary significance of modern epidemics. In addition, this new perspective includes a revision of both the strategy and routine praxis of protective medicine [15]. Reference List 1. Rumyantsev,S.N. Chemical ecology and biomolecular evolution. Acta. Biotheor. 45, 65-80 (1997). 2. Milton K Diet and Primate Evolution in Becoming Human 22-29 (Scientific American, Special edition , 2006). 3. Burgasov PN & Rumyantsev SN Evolution of Clostridiosis [in Russian](Meditsine, Moscow, 1974). 4. Fossey D Gorillas in the Mist.(Houghton Mifflin, Boston, 1983). 5. Meat-Eating and Human Evolution(Oxford University Press, New York, 2006). 6. Milton K A hypothesis to explain the role of meat-eating in human evolution. Evolutionary Anthropology 8, 11-21 (1999). 7. Perry GH, Dominy NJ, Claw KG, & et al Diet and the evolution of human amylase gene copy number variation. Nat Genet 39, (2007). 8. Leonard WR, Snodgrass JJ, & Robertson ML Effects of Brain Evolution on Human Nutrition and Metabolism. Annu. Rev. Nutr. 27, 311-327 (2007). 9. Cuvier G Recherches sur les ossemens fossiles Paris, 1825). 10. Rumyantsev SN & Gerasimov VK The Origin and Functions of Biodiversity in Infectious and Non-Infectious Diseases in Focus on Biodiversity Research (ed. Schwartz J) 199-300 (Nova Science Publishers , 2007). 11. Rumyantsev S.N., Shabalow N.P., Pyasetskaya M.F., Rogacheva N.M., & Bardakova L.I. Species, population and age diversity in cell resistance to adhesion of Neisseria meningitidis serogroups A, B and C. Microbes and Infection 2, 447-453 (2000). 12. Rumyantsev SN Toward Molecular Level of the "Salmonella-Victim" Ecology, Genetics, and Evolution . The Scientific World JOURNAL 1, 193-199 (2004). 13. Rumyantsev SN Biological Weapon. A Terrible Reality? Profound Delusion? Skillful Swindling?(Vantage Press, New York, 2006). 14. Rumyantsev SN Genetic immunity and influenza pandemics. FEMS immunology 48, 1-10 (2006). 15. Rumyantsev SN. Defend only the Defenseless. http://www.scienceboard.net/community/perspectives.84.html . 2007. ### << Previous Next >> [ View All Perspectives ] |
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