Selected elements of the theory described in Death from a Distance and the Birth of a Humane Universe are synopsized in a chapter in this book. The critique below by the editors of this volume refers specifically to this chapter; however, the questions raised also have broader relevance.
“We note that [this] proposal is controversial in various respects. The claim that elite throwing was the core innovation responsible for separating late prehumans from their hominoid ancestors clashes directing with recent work on the evolution of hominin shoulder morphology (Larson, 2007), which indicates elite overhand throwing to have been a more recent development, post Homo erectus. The latter view is supported by Rhodes and Churchill (2008), who date the appearance of long-range projectile weaponry in the human tool kit to no earlier than 80,000 years ago. It is also interesting to note that modern humans display a strong sexual dimorphism with respect to elite overhand throwing: various differences in males versus females conspire to make the former much more effective overhand throwers than the latter. Studies (reviewed in Chimes, 2001) show, moreover, that these differences emerge quite early, in children as young as five years old, and steadily increase thereafter. This trajectory differs sharply from that of natural language, which shows no stable, sex-related differences in the acquisition process, and no persisting differences in adults. A natural conclusion from these results is that, far from being a core innovation in the human lineage, elite throwing was in fact a late evolutionary arrival, and one more probably correlated with specialized male social functions (hunting) than with human society generally.”
Quoted from The Evolution of Human Language (pg 13; edited by linguists Larson, Deprez and Yamakido)
Our response to these authors’ objections:
This critique is illuminating about one class of common theoretical misconceptions regarding cause and effect. When we fail to recognize the central role of the conflict of interest problem in the evolution of elite communication (including language), we are prone to underestimate the crucial importance of the solution to this problem before elite human language can arise. Specifically, the exchange of contingent (potentially false) information is a social enterprise fraught with the potential for individually self-interested hostile manipulation. Only when this problem is controlled can elite exchange of information (including human language, in the narrow sense) evolve.
The underestimation of the conflict of interest problem that centrally limits animal and human communication has been one of the most systematic barriers to insight the linguistic enterprise has yet to overcome. This limitation, in turn, makes it difficult to put the relevant empirical information in perspective. The above critique suffers from this limitation. We rebut each of these objections as follows.
First, Susan Larson’s (2007) analysis of early Homo fossil shoulders is invoked as potentially falsifying the claim that early members of Homo (ca. 1.8 million years ago) were elite throwers, a claim our theory requires to be true (Chapter 5; Death from a Distance and the Birth of a Humane Universe or DfaD, for short). Note that evidence from other fossil Homo structures (including feet, hands and pelves) strongly supports our view and contradicts Larson’s more narrow perspective, focused on a single anatomical structure (Chapter 7; DfaD). Larson’s argument is that the size and placement of shoulder elements (especially the clavicle length) constrain the early Homo shoulder from moving backward beyond the plane of the torso during an overhand throwing motion. She goes on to suggest that the earliest members of our genus may not have been capable of elite modern-like human throwing as a result.
It remains to be independently confirmed that Larson is correct on the details. No other professional anatomists have yet explored this issue, as far as we are aware. However, even if the details of early Homo shoulder anatomy are essentially as Larson claims, her conclusions about elite throwing are open to serious question. The modern human throwing motion yields high projectile velocity from the powerful torque generated by massive leg and trunk muscles (Chapter 7; DfaD), NOT from specific arm angles or positions. Humans throw with similar elite skill using the side-arm and submarine throwing motions. These motions may be less constrained than the overhand motion on Larson’s interpretation of the early Homo shoulder.
More importantly, even contemporary humans have some difficulty bringing their arms behind the plane of the torso in the overhand position. [Stand at attention and try to bring your fully extended natural throwing arm directly overhand behind your head.] Yet the muscle-tendon-ligament structures stabilizing the shoulder joint have sufficient elasticity that the violent torsional movement of the trunk during the elite human throwing motion causes the arm to be very briefly “left behind” in a rearward position only to spring violently forward a few instants later in the throwing motion. [A Google image search under power pitchers from American baseball like “Sandy Koufax”, “Randy Johnson” or Dwight Gooden” produces some useful illustrations of this phenomenon.] The early Homo shoulder joint might have behaved similarly to this modern deployment, perhaps from a slightly different starting position.
Moreover, strong evidence has been found for caching of throwing sized stones (manuports) in large numbers by Homo at least by the 1.8 million year old site at Dmanisi in Central Asian Georgia (R. Ferring and P Rightmire, personal communication). It is difficult to interpret this evidence as other than an indication that elite throwing is already highly evolved by this very early stage in the emergence of Homo.
In summary, the shoulder evidence in isolation is almost certainly ambiguous and too narrowly interpreted. Moreover, the evidence for early elite throwing from manuports and from fossils of anatomical structures other than the shoulder (Chapter 7; DfaD) is extensive and robustly redundant. Thus, this objection by these authors is not a very compelling attempt at falsification of our theory, in our view.
Second, Larson, et al., claim that Rhodes and Churchill’s (2009; there appears to be a typographical error in the reference to this paper in Larson, et al.;see below for correct reference) data should be interpreted to indicate that elite human throwing might be relatively new (ca. 80,000 years old rather than at least 1.8 million years old as our theory requires). What Rhodes and Churchill’s data actually suggests (these authors are appropriately restrained in their interpretation of their data) is that fully modern upper Paleolithic humans may have, on average, a higher level of asymmetric retroversion (unilateral twisting) of the dominant arm humerus (upper arm bone) than Neandertals. This subtle change in structure is expected to be produced by strong, consistent use of the arm in specific ways during life. Contemporary professional American baseball pitchers tend to show this same humeral twisting, for example.
Larson, et al. suggest that this humeral change means that elite throwing is relatively recent. This objection would then presuppose that Neandertals did not throw with the elite skill obvious in contemporary humans. This interpretation is highly questionable on its face, independent of concerns about sample size and other issues (raised by Rhodes and Churchill). The kind of use-related structural change in question typically happens when individuals engage in chronic, unusually intense repetitions of a behavior to which the skeleton is already adapted – again, analogously to contemporary professional baseball players. Though all contemporary humans are born with the potential to throw with elite skill, only those wishing to hypertrophy their skills develop this skeletal signature.
Rather than suggesting that elite throwing is new to modern humans, Rhodes and Churchill’s data are equally well interpreted to indicate the rise of some new cultural function for elite throwing – presumably not baseball. A likely candidate for such a new function comes with the introduction of the atlatl or spear-thrower. This novel weapon is apparently invented at the same time and in the same population where Rhodes and Churchill find evidence for possible enhancement of humeral retroversion (Chapter 11; DfaD). Chronic use of the atlatl (which exploits and amplifies the elite human throwing motion) is an excellent candidate for the origin of the cultural behavior-based bone changes suggested by Rhodes and Churchill’s data. These data certainly do NOT convincingly demonstrate that elite human throwing is only 80,000 years old. Indeed, again, the paleoanthropological record in aggregate strongly suggests a much earlier origin (above; Chapter 7; DfaD).
Third, it is argued that the development of a sexual dimorphism in throwing ability in young contemporary children suggests a very recent origin for throwing behavior. This is not an appealing interpretation. Elite male-dominated societies are probably a relatively recent aberration in the human story (Chapter 13; DfaD) from which we are still emerging. These elite male-centered societies do, indeed, impose various strong sexual dimorphisms on culturally transmitted public behaviors; however, we should not conclude from this that the wearing of blue by some young contemporary boys (for example) tells us much about the 2 million year evolution of human apparel.
Likewise, “throwing like a girl” is quite likely to be a recent, idiosyncratic, culturally imposed sexual dimorphism. Human skills at any behavior, including those to which we are genetically/anatomically adapted, are highly contingent on concordant culturally transmitted information (Chapter 10; DfaD). [Linguistics itself offers an especially power and accessible illustration of this point. We speak English instead of Japanese, say, because of our cultural heritage, not our genetic properties.]
As expected on our theory, the current “Title IX” generation of young American women who grew up playing baseball throw much better than their mothers and grandmothers, on average. [A Google search of ‘throw like a girl Title IX’ is enlightening, for example.] Moreover, any small residual ancestral sexual dimorphism in throwing proficiency would most likely be insignificant given the enormous square-law reductions that elite throwing provides to the costs of coercive social ostracism (Chapter 5; DfaD).
In conclusion, if our theory is confirmed, it will likely prove to be a vital tool going forward in the further understanding of linguists for all interested thinkers and researchers. When our existing biases lead us to potentially “falsify” a correct new theory on the basis of a narrow and superficial interpretation of the evidence, we run the risk of damning everything we do to ultimate irrelevance.
The Evolution of Human Language (Cambridge University Press; 2010; Larson, RK, V Deprez and H Yamkido, eds.)
REFERENCES:
Bingham, PM and Souza, J (2009) Death from a Distance and the Birth of a Humane Universe. BookSurge Press. Charleston, SC.
Larson, SG (2007). Evolutionary transformation of the hominin shoulder. Evolutionary Anthropology 16(5): 172-187.
Rhodes, JA and SE Churchill (2009). Throwing in the Middle and Upper Paleolithic: inferences from an analysis of humeral retroversion. Journal of Human Evolution 56(1): 1-10.
Tags: chapter 10, chapter 11, chapter 13, chapter 5, chapter 7, chapter 9
