8. Scientific and Philosophical Preliminaries
Chapter 8
SCIENTIFIC AND PHILOSOPHICAL PRELIMINARIES
If the biblical Adam is, or was, a historical person who actually lived, then the obvious question arises: When did he live? Given the mythical nature of the primaeval history of Gen 1–11, it is to modern science that we must turn in the attempt to answer this question. Now in one sense science has nothing to contribute positively with regard to this question, since it does not contemplate the existence of such a person. Nevertheless, contemporary scientists are vitally interested in a question that is empirically equivalent to our question—namely, when did human beings first appear in the evolutionary process? ¹ In this part of the book we seek to summarize briefly the scientific evidence concerning human origins with a view toward determining approximately when human beings first began to exist. The historical Adam may then be located around that time.
The quest of the historical Adam brings together a surprising number of scientific fields united in a common quest of human origins, such as palaeontology, palaeoanthropology, palaeogenetics, palaeoneurology, palaeoproteomics, and, one is tempted to say, palaeoarchaeology (really, really old archaeology!). In order to discuss the question of human origins, we must first set the framework for modern science’s treatment of the subject.
TIMESCALES
We begin by looking at the various timescales involved.
Geological Timescale
In terms of the geological timescale (fig. 8.1), our discussion focuses on the third period of the Cenozoic era known as the Quaternary period, which began around 2.5 mya (million years ago) and continues through the present.
Figure 8.1. Geological ages relevant to our investigation. Based on Stringer and Andrews, The Complete World of Human Evolution, 27.
The Quaternary period is divided into two subintervals, the Pleistocene epoch, dating from around 2.5 mya until around 12 kya (thousand years ago), and the Holocene epoch, dating from the close of the last major glaciation around 12 kya until today. It will be during the Pleistocene epoch that the origins of the human race are to be sought.
Figure 8.2. Glacial and interglacial cycles over the past 450,000 years. Based on Sandy Eldredge and Bob Biek, “Glad You Asked: Ice Ages—What Are They and What Causes Them?,” Survey Notes 42 (2010), https://geology.utah.gov/map-pub/survey-notes/glad-you-asked/ice-ages-what-are-they-and-what-causes-them/.
The Pleistocene is the epoch popularly known as the Ice Age, during which a series of glacial expansions (called glacials) and recursions (called interglacials) occurred, each lasting several thousand years (fig. 8.2).² We are ourselves living in an interglacial within the ongoing ice age, which is actually the most recent of a series of at least five such ice ages in Earth’s history.
The ice age of the Pleistocene epoch periodically covered much of northern Europe and Asia in mile-thick ice, forcing human beings in those regions to adapt to and endure the bitterly cold and harsh climate. The glacial and interglacial periods have been assigned many different names in different geographic locales. Particularly important for our purposes will be the Riss (180 kya–130 kya) and Würm (70 kya–10 kya) glaciations in the Alpine region of Europe.
The timeline of the glacial and interglacial stages is calculated by oxygen isotope samples extracted from the seabed. By comparing the ratio between ¹⁶O and ¹⁸O (oxygen with an atomic mass of 16 or 18, respectively), palaeoclimatologists are able to chronicle the glacials and interglacials, high levels of ¹⁸O corresponding to glacial stages and high levels of ¹⁶O to interglacials. One can thus enumerate successive Marine Isotope Stages (MIS) beginning in the present with MIS 1 and working backward, such that odd-numbered stages represent interglacials and even-numbered stages glacials (fig. 8.3). The MIS timescales are often used in dating events taking place in the Pleistocene epoch.
Figure 8.3. Start dates of the most recent Marine Isotope Stages.
Thus, if archaeologists say that an artifact dates from MIS 6, we understand that they mean between 191 kya and 130 kya.
Archaeological Timescales
To complicate matters further, archaeologists have developed a different framework for prehistory on the basis of the manufacture of various stone tools. These so-called lithic industries record the progression in the sophistication of stone tools over millions of years. Unfortunately, archaeologists have not used uniform terminology to describe the timelines in Eurasia and Africa. In Eurasia and North Africa, the earliest period is called the Palaeolithic, the intermediate period the Mesolithic, and the most recent period the Neolithic. Within this chronological framework the adjective lower is further used to indicate an earlier subinterval, while upper indicates a more recent subinterval—for example, the Upper Palaeolithic. In sub-Saharan Africa, the Palaeolithic is called the Stone Age, which is subdivided into the Early Stone Age (ESA), the Middle Stone Age (MSA), and finally the Later Stone Age (LSA). Moreover, there is only a rough correspondence between the respective periods in Eurasia and sub-Saharan Africa (see fig. 8.4).
Figure 8.4. Comparison of archaeological ages in Africa and Eurasia. Numbers indicate successive modes of toolmaking.
Our interest is in the African Stone Age and the Eurasian Palaeolithic, which run all the way from the earliest appearance of stone tools around 2.5 mya until the end of the Pleistocene epoch. Because invention of tools took place at different times among scattered populations, local tool industries are given geographical place-names. Some of the more well-known, with approximate start dates, include the following:
Upper Palaeolithic (50 kya–10 kya)
Gravettian (33 kya)
Aurignacian (37 kya)
Châtelperronian (43 kya)
Middle Palaeolithic (300 kya–50 kya)
Mousterian (160 kya)
Levallois (300 kya)
Lower Palaeolithic (2.5 mya–300 kya)
Clactonian (300 kya)
Acheulo-Yabrudian Cultural Complex (350 kya)
Acheulean (1.7 mya)
Oldowan (>2.5 mya)
There are five broad modes of toolmaking associated with these periods from earliest to latest: (1) Oldowan: chopping tools (ESA, Lower Palaeolithic); (2) Acheulean: bifaces (ESA, Lower Palaeolithic); (3) prepared core tools (MSA, Middle Palaeolithic); (4) blades (LSA, Upper Palaeolithic); and (5) microliths (LSA, Mesolithic). An important question will be what such stone tools enable us to infer about the cognitive capacities of their manufacturers and users.
PALAEOANTHROPOLOGICAL CLASSIFICATIONS
Having established the chronological framework for our investigation, we now need to say a word about the classificatory framework of palaeoanthropology. Roger Lewin and Robert Foley explain that the new genetics has overthrown the traditional classificatory scheme that subdivided the superfamily Hominoidea into three families: Hylobatidae (gibbons and siamangs), Pongidae (orangutans, gorillas, and chimpanzees), and Hominidae (humans) (fig. 8.5).³
Figure 8.5. Traditional classification of apes and humans.
This classification, claim Lewin and Foley, links together too closely the modern great apes, when in fact chimpanzees are more closely related to humans than to orangutans and gorillas. So the better classification, while leaving the Hylobatidae intact, would subdivide the family Hominidae into the Ponginae (orangutans), Gorillinae (gorillas), and Homininae, which comprises both Panini (chimpanzees) and Hominini (humans) (fig. 8.6).⁴
Figure 8.6. Revised classification of apes and humans.
It would be nice to have English equivalents of these Latin terms. Lewin and Foley refer to the Hominoidea as hominoids, the Hominidae as hominids, the Homininae as hominines, and the Hominini as hominins. We shall adopt this vocabulary.⁵
But an important point of clarification remains. While the genus Homo may include today the only representative of the hominins, in the past there were members of another genus, Australopithecus, bipedal apes that most palaeoanthropologists assume to be hominins, part of the lineage leading to modern humans (Homo sapiens) after its divergence about 5–6 mya from the lineage leading to modern chimpanzees.⁶ Moreover, there were other species of Homo about at various times, such as Homo habilis, Homo erectus, and, perhaps the most well known, Homo neanderthalensis, or Neanderthals. So hominins would include both Australopithecines of various species and various species of Homo.
None of these classificatory categories should be equated tout court with the natural kind human being.⁷ We have therefore avoided translating “Homo” as “human” or “man.” In figure 8.7 we see illustrated various members of the hominin lineage going all the way back to Sahelanthropus tchadensis, an apelike creature near the beginning of our lineage.⁸ The last common ancestor of chimps and humans has not yet been identified.
Notice that the species classed as Homo in figure 8.7 should not be automatically regarded as “humans,” in contrast to early hominins and Australopithecines. Such a designation is simplistic and misleading. Ian Tattersall of the American Museum of Natural History explains that the lumping of fossil forms into either Australopithecus or Homo is the result of historical accident. When Carl Linnaeus formulated the traditional classification, there were no hominids other than Homo, and so when other primitive fossil forms began to be discovered they were classed as primitive species of Homo. The Australopithecines were classed as Homo transvaalensis and thought to have evolved into Homo erectus and finally into Homo sapiens. Tattersall complains, “Lumping this huge variety of hominids into the single genus Homo was an act of systematic extremism that in practice made it impossible to characterize the human genus in either anatomical or behavioral terms. Yet the paleoanthropologists capitulated instantly.” Although palaeoanthropologists came to recognize Australopithecus as a distinct genus, “the problem lay in the attempt to divide early hominids into Homo vs australopiths, rather than admitting that the morphological diversity actually seen way back into the early hominid fossil record would best be organized by recognizing more genera.”⁹ Tattersall points out that the early forms classed as Homo, such as Homo habilis, Homo erectus, Homo rudolfensis, and so on, all have in common remarkably small brains, hardly larger than those of the Australopithecines, in conspicuous contrast to Homo sapiens, which has a brain more than twice the volume. Although some palaeoanthropologists have proposed that Homo be limited only to forms that resemble more closely Homo sapiens than the Australopithecines, this “sage advice has been widely ignored.”¹⁰ The recent classification of Homo naledi, a creature with a brain smaller than that of almost any other claimed Homo, illustrates the problem. “The main lesson naledi has to teach us is the futility of trying to divide what is now a very extensive hominid record between australopiths and Homo. There is a lot more systematic structure—a more complex geometry of species relationships—in this record than can usefully be characterized by bundling the very diverse assemblage of hominids now known into one of two predetermined genera.”¹¹
Figure 8.7. Hominin lineages back to Sahelanthropus tchadensis. Based on Ian Tattersall, The Fossil Trail.
WHAT IS IT TO BE HUMAN?
With the above frameworks in mind, we propose to survey some of the scientific evidence from a variety of fields concerning the most likely date of human origins. But first we must figure out exactly what we are looking for.
We have seen that it would be rash to assume that organisms classified as Homo are ipso facto human beings. Rather, we need to specify certain conditions that are jointly sufficient for humanity. There is, in fact, a noteworthy consensus among scientists as to what these conditions are. We are, after all, familiar with ourselves as human beings and therefore know what a paradigmatic human being is like.
Sufficient Conditions for Humanness
We know, for example, that any putative human being must be anatomically similar to ourselves. While a self-conscious, rational extraterrestrial (or even chimpanzee) would be a person, he would not be a human person. This necessary condition of humanness need not involve an exact anatomical match. There is a range of anatomical differences even between modern and archaic Homo sapiens, as we shall see, that do not count against the humanity of the latter. By contrast, no one thinks that given their significant anatomical differences to modern man, Australopithecines, for example, were human beings, despite their having some shared features with humans.¹² They were bipedal apes of various sorts with tiny brains (around 460 cubic centimeters [cm³]) that could not have supported modern human behavior. The question remains as to the degree of anatomical variation that would be permissible for a human being. For example, brow ridges would hardly seem sufficient to disqualify a species of Homo from being reckoned human,¹³ but a small braincase plausibly would, given the correlation between brain size and cognitive capacity.
On the basis of our paradigmatic examples of humans, we can delineate certain features that, given sufficient anatomical similarity, are sufficient (if not necessary) for human personhood. What are some of these features? Anthropologists Sally McBrearty and Alison Brooks list four characteristics of modern human behavior:
•abstract thinking, the ability to act with reference to abstract concepts not limited in time or space
•planning depth, the ability to formulate strategies on the basis of past experience and to act on them in a group context
•behavioral, economic, and technological innovativeness
•symbolic behavior, the ability to represent objects, people, and abstract concepts with arbitrary symbols, vocal or visual, and to reify such symbols in cultural practice ¹⁴
McBrearty and Brooks observe that the standards for behavioral modernity that they apply “are universally recognized and are frequently repeated in the literature.”¹⁵
It is worth pausing to underline the fact that McBrearty and Brooks are not offering anatomical conditions for biological humanness but philosophical conditions for human personhood. To see the sufficiency of these characteristics for human personhood, one has only to ask oneself whether a mere beast could exhibit all these sorts of behavior. Although some glimmerings of some of these behaviors, such as behavioral and technological innovativeness, might appear among nonhuman animals, they will pale next to the degree to which they are found among modern humans, and the combination of all four behaviors would remain unprecedented. To deny the humanity of past individuals anatomically similar to modern humans who exhibited such behaviors would be problematic because (1) it is implausible to think that such behaviors did not require the cognitive capacities of human beings and (2) to deny the humanity of past individuals exhibiting such behavior would permit one similarly to deny the humanity of people living today who share such behavior, which is not only implausible but morally unconscionable.
The more difficult question is whether we can discern when such behaviors first appear in the prehistorical record. Even if we can, it is useful to remember that signs of such behavior give us only the latest date at which humanity came on the scene, not the earliest, and provide an indication of only the minimum level of cognitive capacity of persons exhibiting that behavior, not the maximum level of their cognitive ability.¹⁶
Terminus a Quo and Terminus ad Quem for Humanity
We can set boundaries of our quest for human origins by establishing a terminus a quo and a terminus ad quem for the first appearance of human beings. How far back can the first appearance of humans be extended? Palaeontological evidence continues to push Homo sapiens further and further into the past. The hominin fossils of Jebel Irhoud in Morocco are the earliest fossils of Homo sapiens discovered to date.¹⁷ Layer 7 of the excavation contained the remains of at least five individuals (three adults, one adolescent, and one child). The brain volume of these individuals was large, between 1,300 and 1,400 cm³, comparable to that of modern man (1,100–1,500 cm³). With an age of 315 ± 34 thousand years (as determined by thermoluminescence dating), Jebel Irhoud is the oldest and richest MSA hominin site to document early stages of the Homo sapiens lineage in which key features of modern morphology were established. Although there are differences in the cranial shape of these archaic humans compared to modern humans, specifically their elongated braincase and heavy brow ridges, the excavating archaeologists emphasize that already 300 kya “their facial morphology is almost indistinguishable from that of R[ecent] M[odern] H[umans], corroborating the interpretation of the fragmentary specimen from Florisbad (South Africa) as a primitive H. sapiens tentatively dated to 260 ka.”¹⁸ Moreover, mandibular and dental morphology, as well as the slow pattern of dental development, also align the fossils of Jebel Irhoud with anatomically modern humans. The contemporaneous presence of similar individuals at two ends of the African continent implies that Homo sapiens had become widespread by that time and so may have originated a hundred thousand years earlier. While such skeletal remains alone may not prove the humanity of such individuals, they make it at least possible that human beings date back to over 300 kya.
But what shall we say about earlier forms of Homo? Despite being classified as Homo, so-called Homo habilis was, as mentioned, almost certainly not human, given its brain size of 550–687 cm³.¹⁹ Many palaeoanthropologists would have it renamed Australopithecus habilis. Since it is the earliest species of Homo, dating to around 2 mya, we already have a terminus a quo for the origin of humanity. Human beings, according to the evidence, do not date as far back as Homo habilis. The same can probably be said with respect to the poorly attested Homo rudolfensis, a contemporary of Homo habilis that had a brain size estimated at 526–700 cm³ and that may not even be a distinct species.
Louise Humphrey and Chris Stringer caution that the diversity of hominin fossil remains dating around 2 mya complicates the question of human origins. “Are we defined by our small jaws and teeth, our large brain, our long legs, habitual tool-making and meat-eating, or some combination of these or other traits?” they ask. “If we require the combined presence of several traits to recognize a fossil as human, many of these early Homo specimens are simply too incomplete to make a confident diagnosis, and that is true overall until we arrive at the more complete remains and behavioral evidence of Homo erectus.”²⁰ So long as we have fossil skulls of specimens of early Homo (and Australopithecus), however, the incompleteness of the skeletal remains does not prevent a negative diagnostic judgment excluding a specimen as human on the basis of inadequate brain size.
When we come to Homo erectus, the picture becomes less clear, especially given the lengthy history and geographical spread of this particular hominin. Specimens have been found throughout Asia and Africa over a span of nearly one and a half million years from around 2 mya, thus permitting a plethora of identifiable subspecies. It is possible that some late-developing member of the species might be arguably human, even if more primitive members are not. For example, the very early fossils of Homo erectus from Dmanisi, Georgia, have a brain volume of only about 600 cm³, whereas later specimens from Java reach 1,100 cm³, touching the lower bound of modern Homo sapiens (1,100–1,500 cm³). By the time we get to Homo heidelbergensis and Homo neanderthalensis, brain sizes are large enough (1,100–1,400 cm³ and 1,200–1,750 cm³, respectively) to support human personhood, the brain volume of Neanderthals in fact exceeding that of Homo sapiens, whose brain size has actually been shrinking over the last ten thousand years. So Homo erectus provides a terminus a quo for the origin of human beings.
As for a terminus ad quem, the beautiful cave art from the Upper Palaeolithic found, for example, at Lascaux (17 kya) (fig. 8.8) and Chauvet (30 kya) (fig. 8.9) in France was undoubtedly created by human beings.
Figure 8.8. Cave painting of a horse from Lascaux, France. Photo courtesy of N. Aujoulat, Ministère de la Culture et de la Communication, France.
Figure 8.9. Cave drawing of a pride of lions from Chauvet, France. Photo courtesy of N. Aujoulat, Ministère de la Culture et de la Communication, France.
Indeed, there is a numinous quality about these paintings that takes one’s breath away. Viewing these paintings, we sense ourselves standing in the presence of a “thou,” someone who is one of us. The hand stencils, which are among the oldest forms of cave art yet discovered (fig. 8.10), seem almost to be reaching out across the millennia to touch us.
It is universally recognized that the persons who produced such art possessed symbolic thought so as to be able to represent real animals and scenes via painted images. Any attempt therefore to date the origin of human persons later than the earliest time of such cave art is excluded, thus giving us a terminus ad quem for the origin of humanity.²¹
Figure 8.10. Hand stencils from Sulawesi, Indonesia, dated 35–40 kya. Photograph by Cahyo Ramadhani. Representations of animals are also found nearby.
SUMMARY AND PROSPECT
Human beings, in the full sense of organisms anatomically similar to ourselves and capable of abstract thought; deep planning; behavioral, economic, and technological innovativeness; and symbolic behavior, therefore originated on this planet sometime between the Lower and Middle Palaeolithic (or ESA and MSA). By pushing these boundaries inward, if we can, we now want to try to determine the point of this origin more closely. We shall begin with the evidence of palaeoneurology concerning brain size and development among ancient hominins and then turn to an examination of some of the most noteworthy archaeological discoveries bearing on the origin of modern cognitive capacities.
1. Francesco d’Errico and Chris B. Stringer report, “The question of the origin of the attributes that define us as humans is the subject of a lively debate among scholars from disciplines such as primatology, archaeology, paleoanthropology, genetics, evolutionary psychology and linguistics” (“Evolution, Revolution or Saltation Scenario for the Emergence of Modern Cultures?,” PTRSB 366, no. 1567 [April 12, 2011]: 1060).
2. These are thought to follow so-called Milankovitch cycles, which are determined by the coincidence of changes in the shape of the earth’s orbit, the tilt of the earth’s axis, and the earth’s distance from the sun. These cycles correlate with the Marine Isotope Stages mentioned in the text.
3. Roger Lewin and Robert A. Foley, Principles of Human Evolution, 2nd ed. (Oxford: Blackwell, 2004), 211.
4. A somewhat different classification distinguishes between Hominini (chimpanzees and humans) and Hominina (humans).
5. But it deserves to be emphasized just how biologically uninformative such a classificatory schema is. On this schema, to be a hominin is to be on the lineage eventually leading to modern man, whereas to be a paninin is to be on the lineage eventually leading to modern chimpanzees. The two lineages are thought to have diverged from a last common ancestor about 5–6 mya.
If the divergence is just the separation of two populations (divided by the Rift Valley, for example), and it was only much later that there was any actual change in the morphology, then a hominin would be indistinguishable in the fossil record from the last common ancestor. In other words, if the divergence did not involve a substantial evolutionary change, then a hominin would remain invisible in the fossil record for as long as it takes for drift or selection to produce novelties that we now associate with humans—and there is no reason why this might not have occurred only several million years later. (Lewin and Foley, Principles of Human Evolution, 253)
Worse, on this scenario a hominin may be literally the same sort of organism as one living on the other side of the valley that is not a hominin, which seems perverse. The two organisms are perfectly similar, and all that distinguishes them is the future destiny of their lineages.
So Lewin and Foley muse that “a more practical approach” is to say that a hominin can be recognized from its having present-day (or derived) hominin features such as bipedalism, large brains, small faces, reduced canine teeth, and so on. Now all of these derived features or characters are unlikely to have evolved simultaneously. So bipedalism, as a very complex adaption, is currently thought to be the most diagnostic and significant evidence for the presence of the hominin lineage. On this view bipedalism or other derived characters serve merely as evidence of an organism’s being a hominin but do not constitute it a hominin. But Lewin and Foley report, “The current position is therefore that hominins are defined by bipedalism, and this is the feature to seek traces of in the fossil material. But if it is not present, that would not … necessarily mean that the fossil is not a hominin, merely that we have yet to define what the earliest changes were” (Principles of Human Evolution, 253). This position is unfortunately self-contradictory. If hominins are defined by bipedalism, rather than merely identified by it, then it is impossible that a nonbipedal organism was a hominin. Thus, we seem stuck with the perverse consequences of the current classificatory schema and must accept that early paninins and hominins may actually be the same organisms and so accept the invisibility of early hominins in the fossil record. Lewin and Foley note that the problem becomes even more intractable because there is evidence that bipedalism may not be unique to hominins but may have evolved independently more than once, which undermines even its diagnostic value.
6. The expression “human ancestors” is thus ambiguous and may be misleading. Australopithecines may be said to be human ancestors in the sense that they are (nonhuman) ancestors of humans, but they are not human ancestors in the sense that they are among our ancestors that were human.
7. Ian Tattersall notes that “human” can be taken in either an exclusive or inclusive sense. The inclusive sense (used by Lewin and Foley) means “being related to us by descent”; the exclusive sense applies only to creatures with all the qualities that distinguish us from the rest of the living world. Tattersall muses that these two senses of the word are clearly in conflict. An early member of our lineage need not have possessed any of the qualities of the mind that we see as unique to ourselves (Ian Tattersall, The Fossil Trail: How We Know What We Think We Know about Human Evolution, 2nd ed. [Oxford: Oxford University Press, 2009], 70). Although Tattersall says that the inclusive sense of “human” requires that an organism possess only one or two of the anatomical novelties that Homo sapiens has acquired, Lewin and Foley’s scenario in the earlier note (see note 5) reveals that even that much is not required.
8. Cf. Louise Humphrey and Chris Stringer, Our Human Story (London: Natural History Museum, 2018), 18–19, for a similar chart.
9. Ian Tattersall, “The Genus Homo,” Inference 2, no. 1 (February 2016), https://inference-review.com/article/the-genus-homo.
10. Tattersall, “Genus Homo.” Tattersall has reference to Bernard Wood and Mark Collard’s proposal that membership in Homo requires that any candidate species (1) is more closely related to Homo sapiens than it is to the Australopiths; (2) has a body mass closer to Homo sapiens than to the Australopiths; (3) has reconstructed body proportions that match those of Homo sapiens more closely than those of the Australopiths; (4) has a postcranial skeleton consistent with modern humanlike bipedality; (5) has teeth and jaws closer in size to Homo sapiens than to Australopiths; and (6) shows a modern humanlike extended growth and development life phase. They deny that Homo habilis and Homo rudolfensis should be classed as Homo (Tattersall, Fossil Trail, 271). Having rejected this advice, “scientists are still arguing vehemently over which ancient fossil human relatives should be included in the genus Homo. And they are doing so in the absence of any coherent idea of what the genus that includes our species Homo sapiens might reasonably be presumed to contain” (Tattersall, “Genus Homo”).
11. Tattersall, “Genus Homo.” Schwartz and Tattersall conclude, “If we want to be objective, we shall almost certainly have to scrap the iconic list of names in which hominin fossil specimens have historically been trapped, and start from the beginning by hypothesizing morphs, building testable theories of relatedness, and rethinking genera and species” (Jeffrey H. Schwartz and Ian Tattersall, “Defining the Genus Homo,” Science 349, no. 6251 [August 28, 2015]: 932).
12. The presence of shared physical features (so-called characters) cannot in any case be assumed to indicate even an evolutionary connection between hominin forms, much less their humanity, for environmental factors could drive the independent evolution of certain features—for example, of reduced dentition or gracile skeletal structure—so that the similarities are homoplasies (similar features resulting from convergent evolution). According to Robert Foley, among hominids “very large numbers of characters evolved convergently in different lineages, both closely and distantly related,” so that convergence is “a common and normal part of the evolutionary process for hominids” (“Striking Parallels in Early Hominid Evolution,” TEE 8, no. 6 [June 1993]: 197; cf. Randall R. Skelton and Henry M. McHenry, “Evolutionary Relationships among Early Hominids,” JHE 23, no. 4 [October 1992]: 309–49, who construct a phylogenetic tree of hominin evolution on the basis of seventy-seven traits that are frequently homoplastic; John G. Fleagle, “Beyond Parsimony,” EA 6, no. 1 [1997]: 1, who complains that Ockham’s razor is pretty dull when the most parsimonious tree has 45 percent homoplasy). For example, Australopithecus sediba shares humanlike features in its lower body and hands that “are likely to have developed independently of the processes that produced early Homo in East Africa, showing that selection may have been driving the evolution of ‘human’ traits in different species at this time” (Humphrey and Stringer, Our Human Story, 94; cf. Andrew Du and Zeresenay Alemseged, “Temporal Evidence Shows Australopithecus sediba Is Unlikely to Be the Ancestor of Homo,” SA 5 [May 2019], eaav9038, https://doi.org/10.1126/sciadv.aav9038). What is important with respect to determining humanity is that a certain minimum brain size is a necessary condition for a hominin to be counted as human.
13. The fossil skulls discovered at Muhharet es-Skhūl, Israel, are regarded by most experts as essentially modern, despite their having distinct brow ridges (Tattersall, Fossil Trail, 82). Even contemporary humans may have brow ridges, and they differ from archaic Homo sapiens in this respect only by having a tiny notch in those ridges called the superorbital foramen—hardly grounds for disqualification from the human race!
14. Sally McBrearty and Alison S. Brooks, “The Revolution That Wasn’t: A New Interpretation of the Origin of Modern Human Behavior,” JHE 39, no. 5 (November 2000): 492.
15. McBrearty and Brooks, “Revolution That Wasn’t,” 534. Francesco d’Errico questions the criteria Brooks and McBrearty used to find these criteria. He expresses concern that the criteria are inspired by African MSA and European Upper Palaeolithic material culture, thus courting “the danger of creating a theory that fits one’s expectation” (“The Invisible Frontier: A Multiple Species Model for the Origin of Behavioral Modernity,” EA 12, no. 4 [August 5, 2003]: 188–202, https://doi.org/10.1002/evan.10113. But d’Errico conflates McBrearty and Brooks’s sufficient conditions of humanness with the archaeological signatures of such behaviors (to be discussed below). Only the latter are based on Upper Palaeolithic and LSA features; the modern behaviors they identify are surely not culture-specific but universal. In any case, d’Errico uses these same criteria to show that the African MSA material culture and the contemporary material culture left by Neanderthals in Europe and the Near East exhibit “no dramatic differences … between the two records,” thereby rendering his expressed hesitations academic.
16. Thus, we should not interpret McBrearty and Brooks to be endorsing what Kim Sterelny calls a “simple reflection model,” according to which modern human cognitive capacity is immediately reflected in the archaeological record; rather, their results are consistent with a “niche construction model,” according to which the archaeological signatures of modern human behaviors do not emerge until humans have so shaped their environment that such signatures become selectively advantageous (Kim Sterelny, “From Hominins to Humans: How sapiens Became Behaviourally Modern,” PTRSB 366, no. 1566 [March 27, 2011]: 809–22, https://doi.org/10.1098/rstb.2010.0301). According to Lewin and Foley, for an increasing number of archaeologists, the evidence reveals a gradual emergence of modern human behavior. Once it passed a certain threshold, that behavior appears to have exploded, producing the rich fabric of social complexity associated with the Upper Palaeolithic and LSA. “That explosion was a cultural change, however, not a biological one” (Lewin and Foley, Principles of Human Evolution, 439). For more on niche construction, see Kevin N. Laland, Darwin’s Unfinished Symphony: How Culture Made the Human Mind (Princeton: Princeton University Press, 2017), chap. 9: “Gene-Culture Coevolution”; Agustín Fuentes, The Creative Spark: How Imagination Made Humans Exceptional (New York: Dutton, 2017).
17. J. J. Hublin et al., “New Fossils from Jebel Irhoud, Morocco and the Pan-African Origin of Homo sapiens,” Nature 546, no. 7657 (June 8, 2017): 289–92, https://doi.org/10.1038/nature22336. See also Daniel Richter et al., who call the remains associated with Jebel Irhoud “the oldest reported for H. sapiens” (“The Age of the Hominin Fossils from Jebel Irhoud, Morocco, and the Origins of the Middle Stone Age,” Nature 546, no. 7657 [June 8, 2017]: 293–96, https://doi.org/10.1038/nature22335).
18. Hublin et al., “New Fossils from Jebel Irhoud.” For a striking photo array of Homo sapiens skulls dating from 300 kya to 100 kya and exhibiting a marked variety of shapes and sizes, see Humphrey and Stringer, Our Human Story, 137.
19. Its classification as Homo was due to the historical accident that its discoverer, Louis Leakey, was enamored with Kenneth Oakley’s notion of “Man the Toolmaker,” a notion now abandoned by palaeoanthropologists in view of Australopithecine (not to mention modern apes’) manufacture and use of tools. Homo habilis is associated with Oldowan tools.
20. Humphrey and Stringer, Our Human Story, 94. They note the further complication that the different supposed “Homo” lineages “could … have evolved in parallel from separate australopith-like ancestors,” in which case the members of these lineages “cannot all justifiably be assigned to the one genus Homo” (94). Humphrey and Stringer implicitly reject polygenesis of the human race, as do most scientists today, given the enormous improbability of multiple origins of the same interbreeding species.
21. To see these and other stunning cave paintings in color, go to https://images.google.com and search for “Lascaux cave paintings,” “Chauvet cave paintings,” or “cave art from Sulawesi.”