The Scars of Evolution
Page 18
Far less familiar is the most challenging of all these markers. It is known as the ‘baboon marker’. Its existence was first revealed in 1976 by a team of researchers from the National Cancer Institute in Bethesda, Maryland. Their paper was entitled: ‘Baboons and their close relatives are unusual among primates in their ability to release nondefective endogenous type C viruses’, and the authors were G. J. Todaro, C. J. Sherr and R. E. Benveniste. A subsequent article in Nature by Benveniste and Todaro had a more arresting title: ‘Evolution of type C viral genes; evidence for an Asian origin of man’.
The infectious type C virus identified in the first paper belongs, like the AIDS virus, to the class known as retroviruses. When such a virus infects an animal, the RNA of the virus is converted into DNA inside the cells. This means that it becomes part of the genetic make-up of the infected animal and can be genetically transmitted from parent to offspring. Retroviruses can also be passed on and re-integrated into the DNA of other animals of the same species (as with AIDS), and even on rare occasions into the genetic information of distantly related species.
The type C virus is endogenous only in baboons – that is, it is a normal part of their make-up and has no harmful effect on them. But when it crosses the species barrier it has the potential to cause disease in other primates. The Bethesda team was able to establish that the baboon virus must at one time have constituted a threat to all the primates of Africa except the baboons themselves, because every African monkey and ape species they examined contained, in their chromosomes, viral gene sequences closely related to RNA genomes of the baboon virus; these sequences evolved to act as a kind of antibody, a protection against the baboon virus.
One thing we can deduce is that when the baboon virus first manifested itself it was able to cause – in all primates except themselves – a serious and probably life-threatening disease. Every extant African monkey or ape species carries the protective gene sequence in its chromosomes. If any such species failed to develop this resistance, it failed to survive.
The second thing we can deduce is that the virus was highly infectious. Unlike the AIDS virus, it was certainly not spread mainly by sexual contact. It was almost certainly airborne, because baboons are diurnal ground-dwellers, yet the species affected by the virus include not only other ground-dwellers like the chimpanzee and the gorilla, but also arboreal species like the colobus monkey and even small prosimians living high in the forest, like the bush baby and the galago.
Baboons still carry the virus, but it appears to have lost its virulence in the course of time. By now it constitutes no particular threat to other primate species, even those not carrying the protective marker. These are, of course, the South American and Asian primates whose ancestors were never in the vicinity of the baboons when the plague was at its height.
Among primates, then, the gene sequence (the ‘baboon marker’) is a reliable indication of African origin, just as the sickle-cell gene is in humans. Of the ape and monkey species tested, 23 showed the presence of the ‘baboon marker’ – and they were all African. They included the gorilla and the chimpanzee. Seventeen species, including the gibbon and the orang-utan, lacked the ‘baboon marker’ – and none of them were African.
The most remarkable aspect of Todaro’s discovery emerged when he examined Homo sapiens for the ‘baboon marker’. It was not there. All races of Homo sapiens – including the African races – lack the baboon marker.
Todaro drew one firm conclusion: ‘The ancestors of man did not develop in a geographical area where they would have been in contact with the baboon. I would argue that the data we are presenting imply a non-African origin of man millions of years ago.’
His own choice of a non-African site was Asia. His paper implies that, following the split from the apes, some populations of hominids spread into Asia; that they were therefore absent when the baboon plague erupted; that any hominid population remaining in Africa at that time ultimately died out; and that all extant humans are descended from the Asian émigrés, some of whom returned westward and crossed the Suez isthmus back into Africa.
There is no evidence which actually rules out the hypothesis of an Asian origin. (The theory of descent from an ‘African Eve’ is irrelevant in this context; it refers to a population bottle-neck on the continent of Africa millions of years later, around 200,000 years ago.) Todaro’s scenario, involving dispersal to the East followed later by a trek back to the West, was felt by some to be inherently improbable, but no one suggested any other way of accounting for the absence of the ‘baboon marker’ in man.
A non-African site does not necessarily imply Java or Peking. If the baboon plague broke out during the fossil gap when Afar was flooded, man’s ancestors could have been living on Danakil – then an off-shore island miles away – or somewhere on the opposite shore of the proto-Red Sea. In either case, not even an airborne virus could have reached them, and by the time their descendants found themselves on the mainland, the baboon plague would have lost its virulence and they would never have needed to acquire the protective gene sequence.
The Bethesda findings made one thing perfectly clear. The idea that man’s ancestors left the trees and subsequently spent all their time on the baboon-haunted African savannah has to be discarded. As Sarich said about molecular dating: ‘One no longer has the option’ of clinging to that version of events. Todaro knew that his findings would not be welcomed, but he wrote: ‘As I see it, one of our major functions in the area of research is to act as historians – to report what actually happened rather than what we would have liked to happen.’
He was certainly not reporting what savannah theorists like to think happened. Their reaction to the ‘baboon marker’ discovery was more or less the same as to Alister Hardy – the response was nil. Discussion of human evolution continued along the old familiar lines as if nothing had happened.
But there is a fundamental difference between trying to ignore a new hypothesis and trying to close the mind to new data. ‘I don’t wish to know that’ was a favourite line of patter among cross-talk comedians, but no scientist can resort to it and hope to retain credibility.
In recent years the climate of opinion has begun to change. In 1987 an international conference was held at Valkenburg in the Netherlands, where the pros and cons of AAT were publicly debated, and that event represented some kind of watershed. By now a number of scientists are prepared to endorse the theory as a tenable hypothesis. Others, while remaining neutral, have been willing to offer constructive criticism, provide a platform, or suggest additional lines of enquiry. To all of these I owe a permanent debt of gratitude.
As Michael Ruse observed in a different connection: ‘You can always find some way of propping up a crumbling theory but, if you are prepared to stay with science, then there really does come a time when the facts start to bite.’
For the crumbling savannah theory, that time has arrived.
References
ACKNOWLEDGEMENTS
Marc Verhaegen, 1987. The Aquatic Ape Theory and some common diseases, in Medical Hypotheses, 24, 293–300.
CHAPTER 1
Elliot Smith, 1924. Essays on the Evolution of Man. Oxford University Press, p. 78.
Robert Broom, 1953. The Coming of Man: Was it Accident or Design? H. F. & B. Witherby, p. 10.
CHAPTER 2
Roger Lewin, 1987. Bones of Contention. Controversies in the Search for Human Origins. New York: Simon & Schuster.
Richard E. Leakey, 1981. The Making of Mankind. Michael Joseph, pp. 11–18.
Don Johanson and Maitland Edey, 1981. Lucy: The Beginnings of Mankind. Granada, p. 243.
Victor Sarich and Allan Wilson, 1967. Immunological time scale for hominid evolution, in Science, 158, 1200–1203.
Sherwood Washburn, 1984. Quoted in Roger Lewin, Bones of Contention, op. cit.
David Pilbeam, Feb. 1984. The descent of hominoids and hominids, in Scientific American, p.87.
CHAPTER 3
Charles Darw
in, 1871. The Descent of Man, chap. 2.
G. Schmorl, 1981. Quoted in Peter Medawar, 1981. The Uniqueness of the Individual. New York: Dover Publications.
W. M. Krogman, 1951. The Scars of Human Evolution, in Scientific American, 185, (6), 54–57.
Roger Lewin, 1983. Science, 220, 700–702.
CHAPTER 4
David Attenborough, 1979. Life on Earth. Collins, p. 294.
Jack Prost, 1985. Chimpanzee behaviour models of hominisation, in Primate Morphophysiology, Locomotor Analysis and Human Bipedalism, edited by Shiro Kondo, University of Tokyo Press, p. 299.
Michael H. Day, 1986. Origins and Modes, in Major Topics in Primate and Human Evolution, edited by Wood, Martin and Andrews, Cambridge University Press, chap 9, p. 199.
C. Owen Lovejoy, 1981. The Origin of Man, in Science, 211, 341–350.
Graham Richards, 1986. Freed hands or enslaved feet? in J. Hum. Evol., 15, 148.
Russell Tuttle and David Watts, 1985. The positional behaviour and adaptive complexes of Pan gorilla, in Primate Morphophysiology, op. cit.
R. W. Newman, 1970. Why man is such a thirsty and sweaty naked animal: a speculative review, in Human Biology, 42, 12–27.
Peter Wheeler, 1985. The loss of functional body hair in man: the influence of thermal environment, body form and bipedality, in J. Hum. Evol, 42, 12–27.
W. Lawrence Bragg on Wegener. Quoted in The Listener, 19 July, 1984.
Don Johanson, 1981, op. cit. Chapter 2.
Paul Mohr, 1978, Afar, in Ann. Rev. Earth Planet Sci., 6 145–172.
Leon P. LaLumiere, 1981. The evolution of human bipedalism: Where it happened – a new hypothesis, in Phil. Trans. R. Soc. London, B292, 103–107.
Ernst Mayr, 1963. Population, Species and Evolution. Harvard University Press.
J. Hürzeler, 1960. The significance of Oreopithecus in the genealogy of man, in Triang, 4, 164–174.
Oreopithecus is further discussed in papers, 1986, by Eric Delson; A. Azzaroli, M. Baccaletti, E. Delson, G. Moratti and D. Torr; Terry Harrison; Frederick S. Szalay and John Langdon, in J. Hum. Evol., 15, 164–174.
CHAPTER 5
Desmond Morris, 1967. The Naked Ape. Macdonald & Co.
William Montagna, 1982. The evolution of human skin, in Advanced Views in Primate Biology, Springer-Verlag, 35–42.
Ronald Marks, 1988. The Sun and your Skin, Macdonald & Co.
CHAPTER 6
Harry Nelson and Robert Jurmain, 1988. Introduction to Physical Anthropology. West Publishing Co, 4th edition.
Clifford J. Jolly and Fred Plog, 1987. Physical Anthropology and Archaeology. Alfred A. Knop, 4th edition.
V. E. Sokolov, 1982. Mammal Skin. University of California Press.
Louis Bolk, 1926. On the problem of anthropogenesis, in Proc. Section Sciences Kon. Akad, Wetens, Amsterdam, 27, 465–475.
Stephen Jay Gould, 1977. Ontogeny and Phylogeny. Harvard University Press.
Gary G. Schwartz and Leonard A. Rosenblum, 1981. Allometry of hair density and the evolution of human hairlessness, in Am. J. Phys. Anthrop., 55, 9–12.
R. M. Martin, 1977. Mammals of the Seas. B. T. Batsford.
W. Sokolov, 1962. Adaptations of the mammalian skin to the aquatic mode of life, in Nature, 195, 464–466.
CHAPTER 7
J. S. Weiner and K. Hellmann, 1960. The sweat glands, in Biol. Rev., 35, 141–186.
J. S. Strauss and F. J. Ebling, 1970. Control and function of skin glands in mammals, in Memoirs of the Society for Endocrinology, 18, 341–371.
Knut Schmidt-Nielsen et al., 1957. Body temperature of the camel and its relation to water economy, in Am. J. Phys., 188, 188–189.
Derek Denton, 1982. The Hunger for Salt. An Anthropological, Physiological and Medical Analysis. Springer-Verlag.
W. Hancock and J. B. S. Haldane, 1939. The loss of water and salts through the skin and the corresponding physiological adjustments, in Proc. Roy. Soc., B105, 43–60.
W. Montagna, 1972. The skin of non-human primates, in Am. Zool., 12, 109–124.
W. Montagna, 1982. The evolution of human skin, op. cit. Chapter 5.
William R. Keating et al., 1986. Increased platelet and red cell counts, blood viscosity and plasma cholesterol levels during heat stress and cerebral thrombosis, in Am. J. Med., 81, 795–800.
CHAPTER 8
D. B. Dill et al., 1933. Salt economy in extreme dry heat, in Journal of Biological Chemistry, 100, 755–768.
C. L. Evans and D. F. G. Smith, 1956. Sweating responses in the horse, in Proc. Roy. Soc., B145, 61–81.
Sheila A. Mahoney, 1980. Cost of locomotion and heat balance during rest and running from 0° to 55°C in a patas monkey, in Journal of Applied Physiology, 49, 61–81.
John K. Ling, 1965. Functional significance of sweat glands and sebaceous glands in seals, in Nature, 208, 560–562.
R. Fange, K. Schmidt-Nielsen and H. Osaki, 1958. The salt gland of a herring gull, in Biological Bulletin, 115, 162.
P. Shiefferdecker, 1917. Die Hautdrusen des Menschen, in Biol. Zbl., 37, 536–563.
William H. Frey, 1985. The Mystery of Tears. Harper & Row.
CHAPTER 9
Frederick Wood Jones, 1929. Man’s Place among the Mammals. Edward Arnold.
Alister Hardy, 1960. Was man more aquatic in the past? in New Scientist, 642–645.
Caroline Pond, 1978. Morphological aspects and the ecological and mechanical consequences of fat depositions in wild vertebrates, in Ann. Rev. Ecol. Syst., 9, 519–70.
P. B. Medawar, 1955. The imperfections of man. Reprinted in The Uniqueness of the Individual, 1981, Dover Publications.
Caroline Pond, 1987. Fat and figures, in New Scientist, 4 June, 62–66.
P. F. Scholander et al., 1950. Body insulation of some Arctic and tropical mammals and birds, in Biol. Bull., 99, 225–236.
CHAPTER 10
A. Cryer and R. L. R. Van, 1985. New Perspectives in Adipose Tissue: Structure, Function and Development. Butterworth.
A. Häger, 1981. Adipose tissue cellularity in childhood in relation to the development of obesity, in Brit. Med. Bull., 37, (3), 287–290.
B. Larsson et al., May 1984. Abdominal adipose tissue distribution, obesity, and risk of cardiovascular disease and death: 13 year follow up of participants in the study of men born in 1913, in BMJ, 1401–1404.
John Studd et al, March 1985. Brit. J. of Obstetrics and Gynaecology.
CHAPTER 11
Victor E. Negus, 1929. The Mechanism of the Larynx. Heinemann.
Victor E. Negus, 1965. The Biology of Respiration. E. & S. Livingstone.
Christian Guilleminault et al., 1980. Sleep apnea syndrome: recent advances, in Internal Medicine, 26, 347–372.
Edmund Crelin, Can the cause of SIDs be this simple? in Patient Care, 12, 5.
G. A. de Jonge and A. C. Engelberts, 1989. Cot Deaths and Sleeping Position, in The Lancet, 11 Nov., 8672, 1149–1150.
Michael Campbell and Mike Murphy, March 1987. Cot deaths following thaw, in Journal of Epidemiology.
F. Wood Jones, 1940. The nature of the soft palate, in J. Anat., 74, 147–70.
Jan Wind, 1976. Phylogeny of the Human Vocal Tract. New York Academy of Sciences.
M. R. Mukhtar and J. M. Patrick, 1984. Bronchoconstriction: a component of the ‘diving response’ in man, in Eur. J. Applied Physiology, 53, 155–158.
M. R. Mukhtar and J. M. Patrick, 1986. Ventilatory drive during face immersion in man, in J. Physiol., 370, 13–24.
R. van den Berg and J. Wind, 1987. Has man’s upright posture contributed to speech origin by lowering the larnyx? in Clin. Otolaryngol., 12.
Robert Elsner and Brett Gooden, 1983. Diving and Asphyxia. Cambridge University Press.
M. J. H. van Bon et al., 1989. Otitis media with effusion and habitual mouth breathing in Dutch pre-school children, in Int. J. Pediatri. Otorhinolaryngol., 17, 119–125.
CHAPTER 12
R. D. Martin and R. May, 1981. Outward signs of breeding, in Nature, 293, 7–9.
C. S. Ford and F. A. Beach, 1952. Patterns of Sexual Behaviour. Eyre & Spottiswoode.
K. E. Fichtelius, 1988. Contribution to the discussion on bipedalism, in OSSA, 14, 45–49.
Ronald D. Nadler, 1981. Laboratory research on sexual behaviour of the great apes, in Reproductive Biology of the Great Apes: Comparative and Biomedical Perspectives, edited by Charles E. Graham. Academic Press.
B. M. F. Galdikas, 1981. Orang-utan reproduction in the wild, in Reproductive Biology of the Great Apes, op. cit.
CHAPTER 13
Stephen Jay Gould, 1977. Ever Since Darwin. Penguin Books, 160–167.
Max Westenhöfer, 1942. Der Eigenweg des Menschen. Mannstaedt & Co.
Michael Ruse, 1989. The Darwinian Paradigm. Routledge.
Kerstin Schuitema, 1990. The significance of the human diving reflex. Paper presented at a Symposium on Human Evolution – The Aquatic Ape: Fact or Fiction – Valkenburg, Netherlands, 28–30 August, 1987.
Donald W. Rennie, quoted in The Diving Women of Korea and Japan, by S. K. Hong and Hermann Rahn, 1967, Scientific American, 216, (5).