Fig. 1. A graduate of the University of Arizona hut Seyoum (Chalachew Seyoum) found a fragment of jaw oldest member of the human race during field work in his native Ethiopia in January 2013. Photo from azcentral.com
New discoveries have allowed to clarify the understanding of the early evolution of the human race. In the Afar region (Ethiopia) in the sediments of age 2,80-2,75 million years found a fragment of the lower jaw, referred by American and Ethiopian paleoanthropologists to the genus Homo. Until now, the oldest find of Homo considered upper jaw AL 666-1 age of 2.33 million years. Meanwhile, another team of anthropologists from the United Kingdom, Germany and Tanzania pereizuchila type specimen of Homo habilis (OH7, age of 1.8 million years) and came to the conclusion that early Homo still better to refer to three different species (H. habilis, H. rudolfensis and “early H. erectus»), but not to the same polymorphic species, as suggested by scientists studying early erectus in Dmanisi (Georgia). Three alleged species differ in the structure of the jaws and teeth, but hardly distinguishable on such an important feature as the volume of the cranium, which has been extremely volatile in all three. Either way, the new data show that the genus Homo appeared and began to diverge earlier than previously thought.
The results of two major paleo-anthropological studies published in early March in the journal Nature and Science. Both works shed light on the early stages of evolution of the human species (Homo).
The article of the British, German and Tanzanian anthropologist, published in Nature, are considered new, more accurate reconstruction of the type specimen Homo habilis OH7 (age of 1.8 million years), found in 1960 at Olduvai Gorge in Tanzania. Studied material includes a slightly deformed lower jaw with teeth and two fragments of parietal bones. The authors studied the priceless discoveries using X-ray computed tomography. Understand the structure of posthumous cracks and deformations, scientists reconstructed the shape of the jaw and parietal skull with the maximum possible accuracy.
Comparing the reconstructed jaw (Fig. 2) with other known jaws of early Homo and Australopithecus, and modern humans, chimpanzees and gorillas showed that jaw OH7 «primitive», that is, has a number of archaic features, brings it closer to Australopithecus. This applies primarily to the shape of the dental arch (Fig. 3). For jaw OH7 characterized by long, almost parallel rows of premolars and molars. This suggests a strong prognathism. In other words, the jaw of the individuals on the monkey came forward. Meanwhile, the known finds of early Homo, including those older than OH7, whose jaw had a more “human” appearance. For example, the upper jaw AL 666-1 age of 2.33 million years old, which is still considered the most ancient finding Homo, dental arch is shorter and wider and the tooth rows are not parallel but diverge like the more advanced members of the human race.
Fig. 2. The lower jaw Homo habilis OH7. Left – jaw in the initial state. Different colors show fragments, the relative position of which has been changed in the course of reconstruction. In the center – a three-dimensional reconstruction, based on the correction of post-mortem deformation. Right – another reconstruction, in which the right half of the jaw restored as a mirror image of the left, and third molars (“wisdom teeth”) as a copy of the reconstructed second molars. The length of the scale interval of 2 cm. The image of the article under discussion in Nature
Statistical analysis of the variability of the shape of the dental arch in various representatives of humanoid showed that early Homo range of variability for this trait greatly exceeds anything that can be observed within the same species in modern apes, including humans. For example, the jaw KNM-ER 1482, traditionally assigned to the species Homo rudolfensis, different from OH7 almost as much as the jaw of modern man from the jaws of chimpanzees.
After analyzing the pairwise intra- and interspecific differences in dental arch form in different hominids, the authors came to the conclusion that on the basis of early Homo is quite clearly divided into three clusters, which they tend to be interpreted as three different species: Homo habilis, Homo rudolfensis and early Homo erectus (the latter includes, in addition to the African finds, also people from Dmanisi). In this case the shape of the dental arch habilis more “monkey” (almost to a greater degree than in the Afar Australopithecus), while rudolfenzisov and erectus – more “human” (Fig. 3). Thus, the authors of the article under discussion do not agree with David Lordkipanidze and his colleagues, who on the basis of new data on the skulls from Dmanisi suggested to be one of the earliest Homo choppy sea (see Fifth .: Dmanisi skull showed enormous scope of individual variability of early Homo, «Elements “10/21/2013).
Fig. 3. Comparison of the form of the dental arch of the lower jaw in modern and fossil hominoids using principal component analysis. Different colors highlighted areas corresponding to the modern anthropoid: H. sapiens (modern man), Pan (chimpanzees), Pongo (orangutans), Gorilla (Gorilla). The points that fill the space between modern apes and humans, fossil hominids match. By referring to H. habilis specimens referred OH7, OH13 and ER1802. Jaws AL822, AL400, AL288 Australopithecus afarensis belong; D2735, D2600, D211 – early erectus Dmanisi; ER60K (ER60000), ER1482 – members of the species H. rudolfensis; KP29281 – early Australopithecus A. anamensis. Drawing from the discussed article in Nature
Of course, this conclusion should not be considered final. It is based on a small number of finds and morphological characters. In addition, not all the findings of early Homo fit well into the proposed scheme. For example, the authors note that copies OH65 (1,6-1,8 million years) and the aforementioned AL 666-1 (2,33 million years), usually referred to H. habilis, too much different from the type specimen and OH7 They fit into their concept habilis. These instances are also deprived of the specific characteristics of the front part of the skull, characteristic of H. rudolfensis. The authors admit that they may be, must reconcile with the earlier erectus, but abstain from the final conclusions and leave the question open.
The researchers also calculated the volume endocast (inner cavity of the skull) OH7 based on surviving fragments of the parietal bone. The calculations are based on two alternative ways of parietal reconstruction of the skull and two ways of calculating the volume of the brain in the form of this section, with the result that happened four digits. All are in the range from 729 to 824 cu. cm, which significantly exceeds the previous estimates (647-687 cu. cm) Thus, OH7 had a very voluminous (at the time) the brain, which, oddly enough, combined with the powerful, strongly raised “monkey” jaws. This combination of features is not very consistent with the known hypothesis that the weakening of the jaw and chewing muscles in early Homo was an important prerequisite for the growth of the brain.
New data, along with the previously obtained show that early Homo was characterized enormous range of variability in terms of the brain. Alleged ‘species’ early Homo on the basis of indistinguishable: the ranges of variability almost entirely overlap (Fig. 4).
Fig. 4. Two alternative reconstruction of the crown of the skull and estimate the amount of OH7 endocast in various representatives of early Homo. The red color shows the estimates based on new reconstructions OH7 (black – old reconstruction). Drawing from the discussed article in Nature
These results are somewhat changing ideas about the early evolution of the genus Homo. Anthropologists will long debate about the classification of these forms and how you combine them into a single view or share a few. From an evolutionary point of view it is a question not of principle. In any case, one can hardly assume that early humans lived at the same time in the same territory in East Africa, divided into distinct, reproductively isolated groups that never crossed each other. Apparently, we have a typical picture of the initial stages of rapid morphological divergence, like barbs (barbels) Lake Tana (14 shapes formed there in less than 30 000 years, some ichthyologists consider different types, others – a kind) or cichlid large African lakes (see .: The genomes of African fish clarify the mechanisms of rapid speciation, “Elements”, 09.29.2014). Moreover, this divergence was due to start long before the era when he lived OH7. It should, in particular, from the fact that the jaw OH7 more ancient primitive jaw AL 666-1. So, already 2.33 million years ago, most likely at the same time there were representatives of the human race, vary greatly in the form of the dental arch. Apparently, a common feature of all populations (or species) of early Homo was a high variability in the size of the brain: some individuals are almost did not differ in this parameter from the ancestors, Australopithecus, while others were much more brainy.
The assumption of an early start of the divergence of the genus Homo is consistent with the new discovery, described in the article of anthropologists from the United States and Ethiopia (Fig. 5).
Fig. 5. Jaw oldest member of the human race LD 350-1 and a map of the area of the Afar in northern Ethiopia. Locations hominid and stone tools are marked with asterisks. Discussed finding comes from a location Ledi-Geraru. The length scale of 1 cm segments. The images of the discussed items B. Villmoare et al. and A. Gibbons in Science
A fragment of the lower jaw of ancient Homo was found in January 2013 in the region of Afar (Ethiopia), at the seat of Ledi-Geraru, which still did not find fossil hominids, despite diligent search. In the 30-40 km from this place are the famous location Hadar, dikika and Gon, which found numerous fossil remains of australopithecines and early Homo, as well as ancient tools 2.6 million years of age.
The deposits, which are found in the jaw, enclosed between two layers of volcanic tuff, which managed to date by radiometric methods. These dating, along with biostratigraphic and paleomagnetic data allow reliably determine the age of the jaw: 2,80-2,75 million years. Thus, the owner of the jaw later lived past Afar Australopithecus (the youngest finds of A. afarensis have an age of about 3 million years old) and much earlier than the oldest Homo from Hadar (2.33 million years).
Of course, a piece of jaw with six teeth (canine, two premolars and three molars) – it is a little. But the bone and teeth are well preserved, which allowed researchers to more or less convincingly justify their bold decision include the discovery of the genus Homo (rather than Australopithecus). Authors scrupulously sorted differences between their findings, which received the code name LD 350-1, from the Australopithecus (especially from A. afarensis, which find a marked similarity) and Paranthropus. Most of the features that distinguish a copy from the LD 350-1 Australopithecus, brings him to the people.
Fig. 6. Comparison of Australopithecus afarensis jaw AL 822-1 (left) and the oldest Homo LD 350-1 (right). Image of the additional materials for discussion article B. Villmoare et al. in Science
The most important features are shown in Fig. 6 where the jaw LD 350-1 is compared with the jaw A. afarensis. Australopithecus mental foramen (mental foramen), serving for the passage of nerves and blood vessels (indicated by the red arrow), opens up towards the front and at the bottom of recesses on the side of the jaw (edge recess is outlined in yellow dotted line). At LD 350-1 groove is missing, the corresponding portion of a convex surface, and the mental foramen was called back (as many Homo). In A. afarensis branch of the lower jaw (ramus mandibulae) – large angular plate extending upward from the body of the bone – begins opposite the second molar (M2), whereas the LD 350-1 cutting edge branch shifted back and begins in front of the third molars (M3 ). In addition, the height of the jaw LD 350-1 is approximately the same throughout (as in most Homo), while in the most massive bone Australopithecine front (has a greatest height bicuspids) and tapers behind (under its height lower molars). There are other signs that indicate proximity to Homo. These include the nature of the attrition of tooth enamel and the slope of the outer (buccal), the edges of the molars: in Homo these edges are nearly vertical, Australopithecus, usually beveled.
The shape of the dental arch at the LD 350-1, judging from the debris was primitive, about like H. habilis OH7 (but not like older AL 666-1).
Despite the differences from Australopithecus and some resemblance to Homo, jaw LD 350-1 is hardly a typical jaw early Homo. It has archaic features and is different from habilis jaw and rudolfenzisov. According to the authors, this jaw looks exactly as it should look like the jaw of a transitional form between Australopithecus afarensis and later people like habilis or rudolfenzisy. So LD 350-1 could, if desired, be attributed to the genus Australopithecus (and certainly there is no guarantee that other parts of the skeleton of the Undiscovered individuals were just as “human” as the lower jaw). A similar dilemma faced by paleoanthropologists whenever forms are transitional between previously isolated genera and species. Making Choices sometimes have to almost throw a coin, although scientific articles and is not accepted to write about it (see .: Australopithecus sediba – Australopithecus, like the man, “Elements”, 15.04.2010; note that a decisive argument in favor of the classification A . sediba australopithecine was a small cranial capacity, the size of the brain have been the owner of the jaw LD 350-1, unknown). Nothing so vividly and clearly shows no loyalty to the Darwinian idea of gradual evolution, like those suffering paleoanthropologists trying to draw clear boundaries between the transition smoothly into each other’s views.
Apparently, already 2.8 million years ago, some Australopithecus, similar to A. afarensis, began to evolve into a “human” side – at least in regard to the shape of the jaws and teeth (which they had arms, legs, brains and behavior, we do not know). With this idea in agreement previously found scattered teeth of similar age, including eight teeth KNM-ER 5431 (2.7 million years) of Koobi Fora in Kenya.
If this hypothesis is confirmed by new findings, and indeed it appears that early Homo descended from A. afarensis, you have to admit that some similarities with humans, marked by later representatives gracile australopithecines, such as A. garhi especially A. sediba, is the result of parallel evolution.
Judging by the concomitant fossil fauna, the alleged ancient man lived LD 350-1 in an open and fairly dry place, like a modern African savanna, possibly with gallery forests along the banks of reservoirs. This follows from the abundance of herbivorous mammals and the lack of wood. The possible presence of gallery forests indicate bone deinotherium; fossil of fish, crocodiles and hippos show many ponds. These data are consistent with the accepted views on the importance of climate change and the spread of savannah in the origin of man (see .: The influence of climate on human evolution is confirmed, “Elements”, 07.02.2011).