Ecology: The Biology of Interaction. 6.21. (Supplement) Main Stages of Anthropogenesis
For most of the history of our family, several species of humans inhabited the Earth simultaneously, and only recently has a single species remained — our own. The development of our genus likely followed a single pattern: new species form in small populations and then spread widely across the planet...
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6.20. (Addendum) Biological Features of Humans
D. Shabanov, M. Kravchenko. Ecology: The Biology of Interaction Chapter 6. Human Ecology and Nature Conservation
6.22. (Addendum) Should We Fear GMO Products?
6.21. (Supplement) Main Stages of Anthropogenesis Do not say: "Why were former times better than these?" for it is not from wisdom that you ask this. Ecclesiastes Our family belongs to the order Primates, which includes more than 200 living species. The oldest known unambiguous representatives of our order lived 55 million years ago, but their history can be traced to even earlier times. More than 30 million years ago, Aegyptopithecus inhabited northern Africa — a possible common ancestor of African apes and humans. This was a small arboreal animal. Hominoids (representatives of the superfamily Hominoidea, which unites humans and gibbons) appeared approximately 23 million years ago; their first known representative is Proconsul, an African arboreal ape. The lineage leading to gibbons diverged from the family Hominidae 20 million years ago. The subsequent events of interest to us took place within our own family. The key events relating to the emergence of our genus and species occurred in Africa. The lineage leading to orangutans diverged from ours approximately 14 million years ago, that leading to gorillas approximately 10 million years ago, and that leading to chimpanzees only 5–6 million years ago. Among the earliest known representatives of our lineage after its split from the chimpanzee lineage were Sahelanthropus and Orrorin, both living approximately 6 million years ago. Of known species, Ardipithecus — living 4.4 million years ago — is the best candidate for our direct ancestor. This was a small animal that in all likelihood moved bipedally, although it inhabited forests rather than open terrain. Ardipithecus was the ancestor of the fairly diverse genus Australopithecus (meaning "southern ape"), which appeared more than 4 million years ago and inhabited African savannas, where the advantages of bipedal locomotion were fully realized (Fig. 6.17.1). Those australopithecines most likely to have been our ancestors had a cranial capacity (which provides an estimate of brain volume) of approximately 430–450 cm³ (in chimpanzees approximately 400 cm³; in modern humans approximately 1,300 cm³ on average). [IMG_1] Fig. 6.17.1. Genealogy of our closest relatives according to current understanding. As new data accumulate, this scheme may be revised; however, some of its essential features (for example, the existence of distinct evolutionary lineages of humans and of many species belonging to this group) may be considered firmly established. Bold lines indicate intervals in the history of human species documented by known fossil remains. Note: not all human species are shown here! Large descendants of australopithecines capable of consuming tough plant matter thanks to powerful jaws are assigned to the genus Paranthropus (meaning "beside the human"), while smaller, generalist forms — not specialized for any particular food type or foraging method — are assigned to the genus Homo. For a period, these two genera evolved in parallel, a process that manifested itself in, among other things, an increase in brain volume and an elaboration of the tools used. Distinctive features of our genus include the manufacture of stone tools (Paranthropus probably used only bone) and a larger brain — typically, though with some exceptions, exceeding 600 cm³. That said, stone tool use is not exclusive to humans: chimpanzees capable of using stone tools have recently been discovered in Africa! Approximately 2.4 million years ago, the first members of the genus Homo appeared in Africa. They are assigned to the species H. habilis — Handy Man. These were small individuals, approximately 1.5 metres tall, with a brain volume of 670 cm³, who used crude pebble tools. Coexisting with this species was the somewhat larger (and relatively flat-faced) H. rudolfensis (approximately 2 million years ago, 770 cm³), whose remains were first discovered near Lake Rudolf. H. habilis disappeared approximately 1.5 million years ago, leaving behind promising descendants. Chief among these was H. ergaster — Working Man (1.9–1.6 million years ago, 880 cm³). This species was substantially larger than its predecessors (roughly the size of a modern human), manufactured sophisticated stone hand-axes, and markedly increased the proportion of meat in its diet (through hunting and scavenging). It was probably this species that first began to use fire. The evolutionary leap brought about by the appearance of H. ergaster was so significant that some researchers consider it more appropriate to assign the two preceding species to the genus Australopithecus, and to begin the history of our genus with H. ergaster. From this stage, the dispersal of humans beyond Africa also begins. Remains of H. georgicus, dated to 1.8 million years ago, have been found on the territory of Georgia; this species was at a developmental level intermediate between H. habilis and H. ergaster (brain 600–680 cm³, height 1.5 m, crude stone tools). However, 1.6 million years ago H. ergaster gave rise to another species, H. erectus — Upright Man. Originating in Africa, this species colonized South Asia. A representative of H. erectus from the island of Java was described in its time under the name "Pithecanthropus" — "ape-man." It was once imagined as a stooped, misshapen creature more similar to an ape than to a human. It is now clear that this species had a thoroughly human appearance, differing only in its low forehead (cranial capacity 900–1,100 cm³), prominent brow ridges, and receding chin. This species existed for more than one and a half million years (1.6 million – 50,000 years ago) and colonized vast territories. Moreover, as recent discoveries have shown, the "Pithecanthropus" even mastered seafaring. On the Indonesian island of Flores, remains of a dwarf human species, H. floresiensis, have been found; this species was in all likelihood a descendant of H. erectus and existed there between approximately 95,000 and 13,000 years ago. To reach Indonesia, it or its ancestors must have crossed considerable stretches of open sea. H. floresiensis was very small in stature (approximately 1 m tall, comparable to a three-year-old child), and it was probably H. erectus itself that made the ocean crossing. The small brain size (380 cm³) did not prevent the people of Flores from using fire, making stone tools, and hunting small elephants. Approximately 1 million years ago, H. antecessor — Pioneer Man (brain 1,000 cm³) — arose in Africa from H. erectus. This species colonized southern Europe and lived there approximately 800,000 years ago. It was possibly from this species that H. heidelbergensis — Heidelberg Man — arose in Africa, subsequently spreading widely across Europe. One of the technological innovations associated with this species was the throwing of sharpened wooden spears. In outward appearance these humans closely resembled us, differing only in a weak chin prominence and a number of barely perceptible anatomical features. Approximately 200,000 years ago, Neanderthal Man — H. neandertalensis — evolved from the Heidelberg people. Neanderthal humans existed in Europe and western Asia in the interval 200,000–28,000 years ago, including during glacial periods. They were stocky, physically very strong and robust individuals with a cranial capacity equal to or even greater than that of our species. They made complex tools, buried their dead, and possibly even possessed the rudiments of art. Analysis of genetic material (mitochondrial DNA) from Neanderthal remains showed that they were not a subspecies of our species but a separate species that evolved in parallel with ours (and coexisted with it for a considerable period of time). The debate over the possibility of interbreeding between Neanderthals and our species continues, however. In 2006, the study of chromosomal genes yielded indirect evidence that such interbreeding did occur, as well as new evidence for the genetic isolation of these species. In any case, the evolutionary paths of our species and the Neanderthals diverged more than half a million years ago. The extinction of the Neanderthals is linked to the disappearance of the mammoth fauna at the end of the last glaciation, and may also have resulted from competitive exclusion by our species. The oldest known specimen of H. sapiens (Anatomically Modern Human) dates to 195,000 years ago. This is the so-called Omo I skull (its age was previously estimated as somewhat younger). Our species arose in Africa approximately 200,000 years ago. Roughly three-quarters of our history was spent in Africa. Approximately 60,000 years ago, as a result of some catastrophic event, our species came close to extinction: all subsequent humans are descendants of a small group that may have numbered only a few dozen individuals. Having overcome this crisis, our species began to spread across Africa and Eurasia. Our species differs from other species of our genus in its more slender build, higher reproductive rate, greater aggressiveness, and, of course, the most complex and flexible behavior. The ancient African representatives of our species are assigned to the subspecies H. sapiens idaltu; the later ones, originating in Africa and spreading throughout the world, are assigned to H. s. sapiens. Representatives of the latter subspecies who inhabited Europe during the last 40,000 years are customarily called Cro-Magnons. Following the emergence of the modern human subspecies, its evolution has proceeded primarily through cultural rather than biological inheritance. For most of the history of our family, several species of humans inhabited the Earth simultaneously, and only recently has a single species remained — our own. The development of our genus likely followed a single pattern: new species form in small populations and then spread widely across the planet. Since humans occupy an extraordinarily broad ecological niche, the cohabitation of two or more of their species in the same territory contradicts Gause's competitive exclusion principle. Under such conditions, only one species could inevitably remain. One might suppose that the only species capable of successfully sharing an ecological niche with H. sapiens would have been H. floresiensis. Island life had made this species very small and its ecological niche sufficiently distinct from ours. Unfortunately, the habitats of H. floresiensis were destroyed by a volcanic eruption (species with restricted ranges are critically dependent on the preservation of their habitats).
6.20. (Addendum) Biological Features of Humans
D. Shabanov, M. Kravchenko. Ecology: The Biology of Interaction Chapter 6. Human Ecology and Nature Conservation
6.22. (Addendum) Should We Fear GMO Products?