Hominids, Homonyms, and Homo sapiens
How’s the story of human evolution hanging together these days? There’s no better place to look than the Annual Review of Earth and Planetary Sciences. In the yearly issue released this month, Ian Tattersall and Jeffrey Schwartz gave a pretty thorough overview of the “Evolution of the Genus Homo.”1 Their account is fraught with controversy, confusion and convoluted ideas from the very first sentence.
The controversy does not revolve around whether evolution is true. There is not a hint of idea that anybody anywhere believes that man was created – a belief of the vast majority of Homo sapiens. This is the story, after all, of the evolution of the genus Homo – assuming from the outset that human beings, with all their unique capabilities, are the end result of a mindless, directionless process of natural selection acting on animal ancestors. Does the story cohere? Are scientists in agreement on the big picture? Is the story supported by the available fossil and archaeological evidence? Those are good questions for readers to ask, because the scientific community, by and large, assumes the evolutionary perspective without asking such questions.
The abstract hints that a lot of controversy is about to be revealed. [Note: kyr = thousands of years, myr = millions of years].
Definition of the genus Homo is almost as fraught as the definition of Homo sapiens. We look at the evidence for “early Homo,” finding little morphological basis for extending our genus to any of the 2.5?1.6-myr-old fossil forms assigned to “early Homo” or Homo habilis/rudolfensis. We also point to heterogeneity among “early African Homo erectus,” and the lack of apomorphies [traits restricted to a single species] linking these fossils to the Asian Homo erectus group, a cohesive regional clade that shows some internal variation, including brain size increase over time. The first truly cosmopolitan Homo species is Homo heidelbergensis, known from Africa, Europe, and China following 600 kyr ago. One species sympatric with it included the >500-kyr-old Sima de los Huesos fossils from Spain, clearly distinct from Homo heidelbergensis and the oldest hominids assignable to the clade additionally containing Homo neanderthalensis. This clade also shows evidence of brain size expansion with time; but although Homo neanderthalensis had a large brain, it left no unequivocal evidence of the symbolic consciousness that makes our species unique. Homo sapiens clearly originated in Africa, where it existed as a physical entity before it began (also in that continent) to show the first stirrings of symbolism. Most likely, the biological underpinnings of symbolic consciousness were exaptively acquired [i.e., co-opted from other bodily changes] in the radical developmental reorganization that gave rise to the highly characteristic osteological structure of Homo sapiens, but lay fallow for tens of thousands of years before being “discovered” by a cultural stimulus, plausibly the invention of language.
The article got bogged down in nomenclature and classification from the get-go. “To understand where we stand on this matter today requires briefly looking at the long history of hominid taxonomy,” they said. They began with the man who first put man into a taxonomic scheme: Carolus Linnaeus. The father of taxonomy put Homo sapiens into the Homo genus with the great apes, but by the 19th century, these were divided into their own separate genera. Who’s in the Homo clade, and who’s out? Surprisingly, the history of human-primate taxonomy has undergone repeated reversals by lumpers and splitters (i.e., those who desired large inclusive categories vs. those who preferred tighter organization). In 1856, Homo neanderthalensis was added to our genus. Controversies have flared up ever since with each new fossil, debating whether it belongs inside or outside of Homo (whatever is meant by that flexible category).
A major paradigm about human evolution emerged about the time of the neo-Darwinian synthesis: the lumpers and progressivists carried the day. Tattersall and Schwartz revealed some inside information about the movers and shakers of this paradigm, and what beliefs moved and shook them:
The prewar superabundance of names ultimately led the ornithologist Ernst Mayr (1950) to propose a radical revision of hominid taxonomy, in which he reduced the entire hominid fossil record to a mere three species. In Mayr’s view, the three fell into a single time-transgressive lineage, and all were classifiable within the genus Homo: H.transvaalensis (for what we often nowadays call the australopiths—the early bipedal apes), H. sapiens (including the large-brained Neanderthals and their like), and H. erectus (everything in between). A further motivation for Mayr’s dramatic cleaning up of hominid taxonomy was a theme he had picked up from his fellow evolutionary theoretician, the geneticist Theodosius Dobzhansky (1937, 1944). This was that the hominid ecological niche was simply too “broad” to permit more than one species of the family to exist at any one time: competitive exclusion just would not allow it. English-speaking paleoanthropologists of the period—whose freewheeling tendency to create a fresh name for almost every new fossil that came along had not been underpinned by any noticeable theoretical framework—rapidly capitulated to Mayr’s onslaught, propelled additionally by their wholesale conversion to the tenets of the Evolutionary Synthesis. The Synthesis was a reductionist view of the evolutionary process that was then sweeping Anglophone evolutionary biology, and both Mayr and Dobzhansky were principal architects of its central notion that evolutionary change could be ascribed in virtually its totality to slow generation-by-generation change in population gene pools, under the constant supervision of natural selection.
So one year, a plethora of fossils each have their own genus; the next, they are all lumped into a “catch-all” category called Homo erectus, which is defined as everything in between bipedal apes and modern humans. That paradigm influenced a generation of paleoanthropologists who “capitulated” to the progressive picture of human evolution, but, alas, it was not to last; Louis Leakey “broke the taboo” by naming Homo habilis in 1964, and then came Homo rudolfensis and Homo ergaster. Some cautiously called their fossil finds “Homo sp.” which means “genus Homo, species uncertain.” Tattersall and Schwartz are unimpressed by some of these. “A recent review (Schwartz & Tattersall 2005) has indicated that the australopith resemblances of all of these specimens have quite likely been underestimated; and at best these ‘early Homo’ specimens make up a very motley assortment.” Paleoanthropologists still disagree over what constitutes the genus Homo. Tattersall and Schartz take a narrow view, using six criteria outlined by Wood & Collard. “Effectively, they concluded anything currently known that was more primitive than Homo ergaster … had to be excluded from Homo for the genus to make morphological and phylogenetic sense. We accept this conclusion,” they said. The first entrant they claim for Homo was “Turkana boy,” they said—a fossil “absolutely without precedent” that was the basis for their claim (below) that “our genus was born in a short-term event” with no clear indication why or how. Strangely, “One might reasonably expect that this radically new physical structure would have been accompanied by changes in lifestyle,” they said, yet “The archaeological evidence available to us does not, however, suggest much change at all.” Didn’t Turkana Boy and his parents realize the time had come to invent culture?
Within the article, which invoked the words controversial and debate six times, Tattersall and Schwartz carved out their own opinions. These include (their words in blue):
- None of the bipedal apes before Homo erectus belong in the genus Homo, and there is such a sharp break between them, the change seems almost miraculous: As far as can be told at present, our genus Homo was born in a short-term event, probably involving a modification in gene regulation, that had cascading effects throughout the architecture of the body.
- There is no obvious connection between body or brain size and culture or cognition: Despite a significant increase in average hominid brain sizes compared to the bipedal apes, there is no immediate signal in the record of any major cognitive improvement with the advent of the new body form. Intuitively, this may seem surprising, but in fact, it is a dramatic example of a theme that is found repeatedly throughout the long history of human evolution: that biological and cultural innovations tend not to occur concurrently (Tattersall 1998, 2004). See the 03/02/2009 entry.
- They don’t believe Neanderthals or anyone prior was truly human: “all claimed evidence for symbolic activities among the Neanderthals is highly debatable,” but they only cited references from 1996 and 1999 (cf. 09/23/2008, 08/26/2008, 05/06/2008, 03/18/2008). They also said, Among the Neanderthals, all claimed instances of early symbolism are strongly disputed (Klein 1999), and for Homo erectus, there are no specific claims of this kind at all (although see Holloway et al. 2004 for a general argument for an early establishment of the basis for modern cognition).”
Having carved out their turf among the controversies, they surveyed the fossil evidence for the early bipedal apes, the broad class of Homo erectus, the Neanderthals, and the truly modern humans.
Homo erectus is particularly controversial, because it is such a broad classification. Tattersall and Schwartz find no clear connection between the Asian, European and African specimens lumped into this class. “In his 1950 review, Ernst Mayr placed all of these forms firmly within the species Homo erectus,” they explained. “Subsequently, Homo erectus became the standard-issue ‘hominid in the middle,’ expanding to include not only the fossils just mentioned, but others of the same general period….”. They discussed the arbitrariness of this classification:
Put together, all these fossils (which span almost 2 myr) make a very heterogeneous assortment indeed; and placing them all together in the same species only makes any conceivable sense in the context of the ecumenical view of Homo erectus as the middle stage of the single hypervariable hominid lineage envisioned by Mayr (on the basis of a much slenderer record). Viewed from the morphological angle, however, the practice of cramming all of this material into a single Old World-wide species is highly questionable. Indeed, the stuffing process has only been rendered possible by a sort of ratchet effect, in which fossils allocated to Homo erectus almost regardless of their morphology have subsequently been cited as proof of just how variable the species can be.
By “ratchet effect,” they appear to mean something like a self-fulfilling prophecy: i.e., “Let’s put everything from this 2-million-year period into one class that we will call Homo erectus.” Someone complains, “But this fossil from Singapore is very different from the others.” The first responds, “That just shows how variable the species Homo erectus can be.”
After discussing the variations in Homo erectus from Asia, they said the variation in Africa is even worse: “The various African fossils attributed at one time or another to Homo erectus show less morphological homogeneity than we see in eastern Asia, span a very substantial amount of time and space, and fail to exhibit significant morphological similarities with their counterparts in Java and China.” Do these even belong in the same class, or do they perhaps indicate that upright-walking humans were a diverse lot? In their effort to distance themselves from Mayr, Tattersall and Schwartz reveal their own bias:
The most recent entrant in this category is a hominid braincase (KNM-ER 42700) from Ileret, dated to 1.55 myr ago, that was attributed to Homo erectus by its describers (Spoor et al. 2007). However, this braincase is small and lightly built, and possesses none of the major hallmarks that make the Trinil holotype of that species so distinctive. Instructively, Spoor et al. simultaneously described a penecontemporaneous maxilla, also from East Turkana, as belonging to Homo habilis; and they concluded that multiple species of the genus Homo thus coexisted in the Turkana Basin during the earliest Pleistocene. Yet allocating the Ileret specimen to Homo erectus could only conceivably make sense in the context of the view that Homo erectus is the middle grade of a single, worldwide, variable, and gradually evolving lineage of Homo through the Pleistocene. Ironically, this was precisely the construct that these same authors were busy rejecting in adjacent paragraphs—reminding us just how difficult paleoanthropologists are finding it to shake off Mayr’s linear legacy.
What makes sense to one may not make sense to another. Tattersall and Schwartz continued on, discussing other Homo contenders up to and including the one they felt was the first “cosmopolitan” hominid, Homo heidelbergensis – another group with a “good deal of variation” within that designation. Trying to make sense of the evidence for tool use and its advancement over time, they mentioned the “disconnect between biological and cultural innovations already noted.” What does it mean to find evidence of controlled use of fire, carefully shaped spears used as javelins, and even shelters made out of saplings and stones, if these were not human beings with human-like cognitive abilities? “Clearly, in the heyday of Homo heidelbergensis we encounter evidence of a cognitively much more complex hominid than any known in the earlier record—although, significantly, there is no artifact known in this time frame that can unambiguously be interpreted as a symbolic object.” Another scientist might respond that absence of evidence is not evidence of absence. How many artifacts from modern hunter-gatherers would remain over the passage of time?
From their section on Homo erectus, they went on to discuss the “out of Africa” consensus, the Neanderthal phenomenon, and the subsequent domination of modern humans. Tattersall and Schwartz denied again that Neanderthals were in full possession of the cognitive skills of modern humans: “They were clearly complex beings with a subtle relationship to their environment (and presumably toward each other), but they evidently did not relate to the world around them in the way in which we do.” They base this on scanty evidence otherwise. “None of this implies, however, that the Neanderthals were not complex and resourceful beings.” But were they human beings? or just animals, as resourceful as squirrels or crows? To think so raises the question of human nature itself. What led to the explosion of cognition and culture that has characterized the beings who invented agriculture and civilization? The question provided another opportunity for a jab at Mayr:
Apart from the advocates of the multiregional hypothesis, who find evidence for the origins of today’s regional groupings of mankind deep in time (e.g., Smith 1984, Wolpoff et al. 1984, Wolpoff & Caspari 1997), there is more or less complete consensus among paleoanthropologists that Homo sapiens originated relatively recently, somewhere in Africa. And certainly, it is in Africa that we find the first hints not only of hominids with modern anatomy but also (significantly, rather later in time) of hominids showing stirrings of the unique cognitive pattern that makes Homo sapiens so remarkable today. Today’s single surviving hominid species is strikingly derived in many features that range from its globular cranium and retracted face to its barrel-shaped thorax; but discussion of the origin of this distinctive entity has alas been muddied by a post-Mayr tendency among paleoanthropologists to admit to Homo sapiens virtually any reasonably recent and large-brained hominid, regardless of its morphology.
Who is calling whose views muddied? It is conceivable that the pendulum of consensus could swing either way again. Some future day, a writer for Annual Review might bemoan the post-Tattersall tendency to define Homo sapiens too narrowly It is not clear on what basis Tattersall and Schwartz can make an incontrovertible judgment.
One thing is clear from the above paragraph: they have disavowed, again, any connection between the anatomy of humans and their cultural abilities – both in time and space. They just said that the “stirrings” of human cognition appeared significantly later in time once their fully human anatomy had evolved. What clicked to “turn on” the uniquely human mind? “Clearly, in Africa, a great deal of innovation was occurring in the genus Homo during the late Pleistocene, and it was out of this ferment that Homo sapiens was born,” they claim, “but the sketchy nature of the fossil record currently at hand makes it possible to glimpse only very dimly the context out of which our species emerged.” So the human mind, with all its talents, just “emerged”? How did that happen? We need only read the next section, “The Emergence of Cognitively Modern Humans.”
Unusual though Homo sapiens may be morphologically, it is undoubtedly our remarkable cognitive qualities that most strikingly demarcate us from all other extant species. They are certainly what give us our strong subjective sense of being qualitatively different. And they are all ultimately traceable to our symbolic capacity. Human beings alone, it seems, mentally dissect the world into a multitude of discrete symbols, and combine and recombine those symbols in their minds to produce hypotheses of alternative possibilities. When exactly Homo sapiens acquired this unusual ability is the subject of debate (contrast Tattersall 1998, 2004 with McBrearty & Brooks 2000). How, exactly, this ability was acquired is even more controversial (contrast Deacon 1997 with Wynn & Coolidge 2004). Symbolic and nonsymbolic cognitive states are clearly separated by a qualitative gulf: The former is not simply an extension of the latter, a little bit more of the same. How that gulf was bridged in the evolution of Homo sapiens, and what the neural mechanisms are that permitted it, remain unclear. Still, by looking for evidence of expressly symbolic activities in the archaeological record of early hominid behaviors, it is possible to sketch, at least tentatively, the context in which this astonishing transition took place.
All they can promise is the where and when, not the how, in other words. They claim evidence for increase in cranial capacity over time among multiple hombres: Homo erectus, Homo neanderthalensis, and Homo sapiens. “What it was that propelled such independent increase is unknown, and is something that will have to be understood if we are ever to develop a full account of the evolution of human cognition.” Maybe it was dark matter or dark energy. Whatever it was, by the end of the trend, human cognition was in evidence – about 100,000 years ago in Africa, they claim, though “The earliest such evidence is highly inferential….”
We can reasonably take evidence of the kind just quoted that the unique human sensibility had begun to stir in Africa—and possibly beyond—in the period beginning approximately 100?80 kyr ago; and we can be sure that the human creative impulse had bloomed fully by approximately 40 kyr ago, because once in Europe, the Cro-Magnons produced a dazzling record of creativity that included cave paintings, engravings, sculptures, annotated plaques, musical instruments, and much other evidence that they were entirely modern in the cognitive as well as in the physical sense (Marshack 1985, 1991; White 1986, 1989). But even at 100 kyr, we are well beyond the origin of Homo sapiens as an anatomical entity.
They have just claimed that Homo sapiens spent 60,000 years as virtual zombies in terms of human intellectual and cultural ability. They had bodies indistinguishable from ours. What happened 40,000 years ago? Here, they suggest it was distant latent ability – a proclivity – waiting silently for up to 160,000 years for the right occasion to explode:
Alternatively, though, it is possible to suggest that the potential for symbolic thought was born in Africa, possibly as much as 160?200 kyr ago, in the major developmental reorganization that also gave rise to Homo sapiens as a distinctive anatomical entity (Tattersall 1998, 2004, 2007). That potential then lay unexpressed until it was discovered through a cultural (nonbiological) innovation, as was suggested by Randy White as early as the 1980s. Plausibly this behavioral innovation was the invention of language, the ultimate symbol-dependent activity. Language also has the advantage in this context of being an externalized possession (Tattersall 2007), rather than an internalized one such as theory of mind, another capacity that has been proposed as the essential underpinning of complex human consciousness (see review by Dunbar 1997).
Within this framework, we can see in expressions such as those of Blombos the initial explorations of a preexisting capacity. The new proclivity could then have been spread culturally via contact with, rather than replacement of, neighboring populations of Homo sapiens. It may even be that its possessors discovered their new behavioral potential independently in multiple places. Whatever the case, the unique human capacity was in full flower by Cro-Magnon times—and the subsequent history of mankind has essentially been one of its ongoing exploitation.
We think of a teen-ager saying “whatever” in a droll voice as an expression of apathy or laziness. Is this intellectual laziness here, to relegate to “whatever it was” as the best scientific explanation for the remarkable flowering of the human mind? Whatever.
Nevertheless, Tattersall and Schwartz congratulated themselves on offering a scientific theory of the origin of the human mind, not by divine creation, but by evolution (if you’ll pardon the dissing of Darwin):
In light of all this, we can see the origin of our unique form of consciousness not in an improbable process of long-term fine-tuning by natural selection, but rather as the result of a routine evolutionary event of exaptation (Gould & Vrba 1982), and its unusual dimensions as a function of emergence, whereby a long accretionary evolutionary history had culminated in a small modification that gave rise to an entirely unanticipated level of complexity (Tattersall 2004, 2007)
In their view, latent abilities are a “function of emergence” (the unexplained appearance of unanticipated properties from pre-existing materials). These latent abilities sit idle for sometimes hundreds of millions of years, till after a “long accretionary evolutionary history,” some unknown and unanticipated event switches that potential on. The latent ability is “exapted” (i.e., adapted without foresight) and evolutionary history takes a new turn. For a stinger, what do they call the best evidence that modern man had finally arrived? He wiped out all the contenders: “the spread of symbolic Homo sapiens around the Old World was accompanied everywhere by the rapid demise of resident hominid species. This, as much as cave art that is as powerful as anything ever wrought since, speaks for the emergent and absolutely unprecedented nature of symbolic Homo sapiens.” Yes, man the genocidal maniac had finally arrived.
The authors end with a Disclosure Statement: “The authors are not aware of any biases that might be perceived as affecting the objectivity of this review.”
The authors may not be aware of their biases, but we sure are. Look, folks: if you for a minute think that this hodgepodge of guesswork, ad-hoc speculation, and dogma masquerading as knowledge deserves to be blessed with the appellation of science, you need a serious deprogramming session. We don’t have to prove it. We just have to quote what they said, and allow them to prove their own inanity by their own words. Look: they appealed to mystical forces, happenstance, chance, luck, lack of evidence and lack of knowledge, debate, controversy, dogma and naturalistic miracles to state their case. This is no better (except for the prestige of the journal in which it got published) than some late night talk show host telling us space aliens planted the human mind in an ape’s body. Understand this: fossils are real, skulls are real, cave paintings are real, and continents are real – but they do not interpret themselves. What did these guys just tell us? They did not appeal to scientific facts or evidence so much as to a “framework” (a crystal ball, a tool of divination), in which it becomes possible to “glimpse very dimly” the “light” of mystical understanding.
When the exceptions outnumber the rules, you should be alert that something is seriously wrong. Let’s reinforce the sense of how much rationality you would have to jettison to accept Tattersall and Schwartz’s belief system. You have to first distance yourself from other eminent evolutionists, like Ernst Mayr (the ornithologist styling himself an expert on human origins), and all the other paleoanthropologists who disagree with them. Then you have to look at an assemblage of human fossils from all over the world and make arbitrary judgments about who’s in and who’s out (a kind of historical racism). Then you have to accept uncritically a dating framework that was set up to glorify Charles Darwin. Then you have to accept the validity of arguing from silence, as well as tossing out the evidence you don’t like. Then you have to make arbitrary judgments and distinctions about what kinds of bodies are more primitive or advanced (their euphemism is “derived”). Then you have to separate in your mind any necessary connection between morphology and intelligence, or brain size and intelligence. Then you have to call your fellow men and women zombies – your equals or superiors in physical fitness – but who, for unknown reasons, for nearly two million years, though talented enough to make spears and hunt wooly mammoths with team effort (could you do that?) couldn’t figure out that their tongues and throats and brains were designed for language, and their hands for art, and their minds for understanding. Then you have to accept the premise that chance “proclivities” can lay fallow for millions of years, only to be “discovered” by Charlie the cobbler after Tinker Bell zaps some unspecified gene with her mutation wand, producing a whole cascade of effects that produces an instant Homo sapiens. Then you have to wait for another 35,000 years for your fully modern, clear thinking, artistically-proficient, music-making brethren to think hard enough to realize that they might save a lot of time and energy by learning how to ride a horse, invent a wheel and plant seeds. On top of all this, after relegating scientific explanation to “whatever it was” that just “emerged” from some unspecified “proclivity” that also just emerged, and telling us they have no bias, they have the gall to tell us what makes sense. Jargon or no jargon, skull measurements or no skull measurements, this whole belief system is pathetic. Calling this science is sick. It is evidence for the decline of the human mind starting around 1859.