Becoming Human, Becoming Parasitized
It is now generally accepted that Africa was the cradle of humanity. The earliest evidence of hominids, that is, animals ancestral to modern humans and not closely related to other monkeys and apes, is found in Africa. The evidence for this comes from unearthed bones and teeth (fossils). The fossil record shows that one of our oldest ancestors—called Australopithecus—lived in Africa about 4.2 million to 3.8 million years ago. These early hominids, which split from the ape lineage (and were discovered in Kenya in1994), are named A. anamensis, and to judge from the structure of the teeth and the position of the opening where the spinal cord enters the skull, one can conclude that they were apelike humans, not apes. Our ancestor Australopithecus spent time in trees and basically behaved similarly to chimpanzees, or so we believe, since fossils provide no record of behavior. Whether A. anamensis walked on two feet is uncertain, but evidence for erect, upright posture in Australopithecus comes from bones discovered in Ethiopia and Tanzania that are 3.8 million to 3.0 million years old, from a species named A. afarensis. One of these finds, a small female, was discovered and named Lucy by Donald C. Johanson of the University of California at Berkeley. The limb structure and the way the hip joint and pelvis articulate make it clear that Lucy walked on two legs (Fig. 2.2). This was dramatically shown by Mary Leakey and her team, who discovered three sets of fossilized footprints left in wet volcanic ash some 3.2 million years ago. A. afarensis weighed about 75 lb and was not very “brainy,” its brain being no larger than the brains of living African great apes. When A. afarensis descended from the trees and stood upright with two feet firmly planted on the ground, not only did it affect posture, but it dramatically changed lifestyles and diets, and disease patterns began to be altered.
Descent from the trees to the ground placed the australopithecines into a new environment, an ecological niche that was very different from the forest canopy. This freed them from some diseases but allowed for the acquisition of new ones. For example, in the treetops australopithecines would have been bitten by mosquitoes that carried parasites acquired from other animals living in the canopy, but at ground level they would be exposed to other airborne bloodsuckers such as ticks and flies, or they would come in contact with different food sources and contaminated water. Their teeth were small and underdeveloped, as in modern human beings, and the canines, highly developed in existing ape species, were small like ours. We can infer from their teeth that these australopithecines probably chewed fruits, seeds, pods, roots, and tubers. Since no stone tools have been found associated with the fossils, it is believed that A. afarensis did not make or use durable tools or understand the use of fire. They were opportunistic scavengers or vegetarians. The life span of an australopithecine has been estimated to have been between 18 and 23 years.
Figure 2.2 Australopithecus reconstruction of Mr. and Mrs. Lucy.
Courtesy of Ken Mowbry, American Museum of Natural History
Beginning about 3 million years ago, the climate in Africa changed from tropical warm and wet to a more temperate cool and dry one, and as a consequence, the dense woodlands were replaced by more open grassy habitats, a savannah. This climate change presented a challenging environment for the woodland-dwelling australopithecines. Although we do not know whether the climate change triggered it, at about this same time, ~2.5 million to 1.8 million years ago, there appear in the fossil record several different kinds (species) of hominids, with two or three coexisting species in eastern and southern Africa. One of these species was A. boisei, a small-brained vegetarian, and the other was Homo habilis (Fig. 2.3b). The name Homo habilis, or “handy man,” is based on the fact that altered stones and animal remains have been found with the fossil bones. H. habilis was more than a scavenger and a gatherer. H. habilis was also a hunter who made and used stone tools: simple stone flakes, scrapers and “choppers” that were chipped from larger stones (Fig. 2.3a). (These stone tools, first found in Africa’s Olduvai Gorge, are called Oldowan tools.) The fashioning of tools suggests a great leap in human intelligence and begins the technological changes that would forever mark Homo as a tool maker and a tool user. H. habilis used the flake tools to cut up the carcasses of the animals that were killed; these were transported to a home base where the meat was fed upon. H. habilis, with a somewhat larger brain, was “smarter” than A. afarensis, but the fossil finds tell us nothing of the numbers of individuals, whether there was division of labor among males and females, or anything about their behavior. We speculate, however, that there were 50 to 60 individuals in a group living in an area of 200 to 600 square miles. We imagine that H. habilis lived at the edge of shallow lakes and in crude rock shelters.
Figure 2.3a Oldowan tools used by Homo habilis, Courtesy Didier Descouens, CC-BY-SA 4.0
There is no fossil record of the parasites that afflicted H. habilis since their soft bodies have disintegrated over time, but we do know that with meat eating came an increase in parasitism. As these nomadic hunters encountered new prey, they met new parasites and new vectors of parasites. The result was zoonosis; that is, animal infections were transmitted to humans. What were these zoonotic infections? We surmise that the parasites of H. habilis were those acquired from the wild animals that were killed and scavenged. The butchered meat might have had parasites such as the bacteria anthrax and tetanus, the roundworm that causes trichinosis, and a variety of intestinal tapeworms. H. habilis would probably have been bitten by mosquitoes, ticks, mites, and tsetse flies, and probably also had head lice. H. habilis also may have suffered from viral diseases such as the mosquito-transmitted yellow fever, as well as non-vector-borne viruses that cause hepatitis, herpes, and colds, and he may have had spirochete infections such as yaws. It is doubtful, but H. habilis could also have been infected with the parasites that cause sleeping sickness, malaria, and leprosy. They certainly must have been infected with filaria, pinworms, and blood flukes, but probably did not have typhus, mumps, measles, influenza, tuberculosis, cholera, chickenpox, diphtheria, or gonorrhea. At the time when H. habilis roamed the African savannah, the human population was quite small, consisting of about 100,000 individuals, and we expect that rates of human-to-human transmission of parasites were low.
Figure 2.3b Diorama in the Nairobi National Museum of Homo habilis,
CC-BY 2.0, https://www.flickr.com/photos/ninara/17147417090/; CC-BY 2.0 license
Figure 2.3c Acheulean tools used by Homo erectus, Courtesy Didier Descouens
Figure 2.3d Diorama of H. ergaster the “African equivalent” to fossils of H. erectus. Alamy Stock Photo.
