Re: [Marxism] So it's not the opposable thumb, after all?

[Rod Holt <rholt@xxxxxxxxxxxxxx>]

Brian Shannon wrote:

> News
> Published online: 17 November 2004; | doi:10.1038/news041115-9
> Distance running 'shaped human evolution'
> Michael Hopkin
>
> Our African ancestors may have been talented endurance athletes.
>
> Long-distance running was crucial in creating our current upright body
> form, according to a new theory.

(snip)

Although I am no expert, I found a substantial difference between the
article by Bramble and Lieberman and the one quoted from the same
magazine by Michael Hopkin.

> Mike Friedman (11/18/04) was certainly correct to say, “I don't buy
> the argument that long-distance running ‘was crucial in creating our
> current upright body form.’” Fortunately, the excellent article by
> Bramble and Lieberman did not make such a claim. Rather, they
> presented anatomical evidence to show that the abilities of humans to
> run rapidly for long distances should be included in any discussion of
> human evolution. Throughout, they assume that pre-Homo genus all
> walked exclusively upright.
> The entire paper is well worth reading, particularly in light of the
> articles on Homo floresiensis published 2 weeks earlier in Nature
> (vol. 431, October 28, 2004).
> The paper concerning endurance running is much too long to put in
> Marxmail and the illustrations are essential. Since one needs to be a
> subscriber to Nature to obtain the article on line, I present excerpts
> below with footnotes, references and illustrations removed, and my
> remarks in square brackets. I include the author’s last paragraph
> which carries their perspective fairly enough. The body of the paper
> is devoted to an extensive review of biomechanics, fossil evidence,
> and an evaluation of other established evolutionary hypotheses.
> -rod
> Nature, vol. 432, pages 345 - 352 (18 November 2004)
> Endurance running and the evolution of Homo
> By Dennis M. Bramble and Daniel E. Lieberman
>
> [Their first paragraphs.] Striding bipedalism is a key derived
> behavior of hominids that possibly originated soon after the
> divergence of the chimpanzee and human lineages. Although bipedal
> gaits include walking and running, running is generally considered to
> have played no major role in human evolution because humans, like
> apes, are poor sprinters compared to most quadrupeds. Here we assess
> how well humans perform at sustained long-distance running, and review
> the physiological and anatomical bases of endurance running
> capabilities in humans and other mammals. Judged by several criteria,
> humans perform remarkably well at endurance running, thanks to a
> diverse array of features, many of which leave traces in the skeleton.
> The fossil evidence of these features suggests that endurance running
> is a derived capability of the genus Homo, originating about 2 million
> years ago, and may have been instrumental in the evolution of the
> human body form.
> Most research on the evolution of human locomotion has focused on
> walking. There are a few indications that the earliest-known hominids
> were bipeds, and there is abundant fossil evidence that
> australopithecines habitually walked by at least 4.4 million years
> (Myr) ago. Many researchers interpret the evolution of an essentially
> modern human-like body shape, first apparent in early Homo erectus, as
> evidence for improved walking performance in more open habitats that
> came at the expense of retained adaptations in the australopithecine
> postcranium for arboreal locomotion. Although the biomechanics of
> running, the other human gait, is well studied, only a few researchers
> have considered whether running was a mode of locomotion that
> influenced human evolution. This lack of attention is largely because
> humans are mediocre runners in several respects. Even elite human
> sprinters are comparatively slow, capable of sustaining maximum speeds
> of only 10.2 m s-1 [23 mph] for less than 15 s. In contrast, mammalian
> cursorial specialists such as horses, greyhounds and pronghorn
> antelopes can maintain maximum galloping speeds of 15–20 m s-1 [34-45
> mph] for several minutes. Moreover, running is more costly for humans
> than for most mammals, demanding roughly twice as much metabolic
> energy per distance traveled than is typical for a mammal of equal
> body mass. Finally, human runners are less maneuverable and lack many
> structural modifications characteristic of most quadrupedal cursors
> such as elongate digitigrade feet and short proximal limb segments.
> However, although humans are comparatively poor sprinters, they also
> engage in a different type of running, endurance running (ER), defined
> as running many kilometers over extended time periods using aerobic
> metabolism. Although not extensively studied in non-humans, ER is
> unique to humans among primates, and uncommon among quadrupedal
> mammals other than social carnivores (such as dogs and hyenas) and
> migratory ungulates (such as wildebeest and horses). Here, we review
> the evidence for and impact of ER in human evolution. We begin with a
> discussion of the mechanical differences between walking and running,
> and how well humans perform at ER compared to other mammals. We then
> review what is known about the key structural specializations thought
> to underlie human ER capabilities, the extent to which they may be
> features that evolved originally for bipedal walking, and the evidence
> for their appearance in the hominid fossil record. We conclude by
> outlining some hypotheses for why ER capabilities initially arose in
> the genus Homo, and the significance of this behavior for human
> evolution.
> --------
> …Average ER speeds for recreational joggers range between 3.2–4.2 m
> s-1 [9 mph].From an evolutionary perspective, it is important to note
> that human ER speeds are exceptional compared to non-human primates.
> Apes such as chimpanzees, and other primates, such as patas monkeys,
> can sprint rapidly, but they do so rarely and only for short
> distances. No primates other than humans are capable of ER.
> … Human ER speeds exceed the preferred trotting (3.1 m s-1) and the
> trot–gallop transition (4.4 m s-1) speeds of ponies (110–170 kg)
> [240-375 lb.], and even the preferred trotting speed predicted for a
> 500-kg quadruped. … Most cursorial quadrupeds such as zebra,
> antelopes, and African hunting dogs trot when running long distances, …
> … human ER speeds are quite comparable to the preferred galloping
> speeds that cursors use over longer distances and times. Minetti has
> shown that sustainable galloping speeds in horses decline considerably
> for runs longer than 10–15 min, accounting for the average daytime
> speed of 5.8 m s-1 [13 mph] at which long-distance postal horses were
> consistently run for millennia. Wildebeests ( 100 kg) prefer to canter
> at 5.1 m s-1. Well-conditioned human runners exceed the predicted
> preferred galloping speed for a 65-kg quadruped and can occasionally
> outrun horses over the extremely long distances that constrain these
> animals to optimal galloping speeds, typically a canter.
> … This is not to say that humans can outdistance specialized
> quadrupeds. Some horse and dog breeds, for example, can be made to run
> more than 100 km day-1 while carrying or pulling a human. Such extreme
> and human-induced feats, however, should not detract from the fact
> that humans can and do run long distances well, despite a primate
> ancestry.
> --------
> The ER capabilities of Homo raise several additional questions, the
> first being whether long-distance running was an important behavior in
> human evolution or merely the by-product of enhanced walking
> capabilities. Traditional arguments have favored the latter
> hypothesis; several of the derived features of Homo in Table 1 are
> proposed as adaptations to improve long-distance walking performance
> in more arid, open habitats. These features include relatively longer
> legs, larger hindlimb and vertebral joint surfaces, narrower waists
> and shorter toes. Yet walking alone cannot account for many of the
> other derived features because the mass-spring mechanics of running,
> which differ fundamentally from the pendular mechanics of walking,
> require structural specializations for energy storage and
> stabilization that have little role in walking. …
> -------
> Considering all the evidence together, it is reasonable to hypothesize
> that Homo evolved to travel long distances by both walking and
> running. New fossils and more detailed analyses of the existing fossil
> record are needed to test whether these two locomotor capabilities
> emerged concurrently or whether ER evolved after selection for
> long-distance walking. An even more difficult task is to determine
> what behaviors selected for ER in the first place. Why would early
> Homo run long distances when walking is easier, safer and less costly?
> One possibility is that ER played a role in helping hominids exploit
> protein-rich resources such as meat, marrow and brain first evident in
> the archaeological record at approximately 2.6 Myr ago, coincident
> with the first appearance of Homo.
> …
> Additional research will help to clarify and test when and how ER
> capabilities evolved in humans, and to examine more thoroughly their
> implications for human evolution. For example, it is known that major
> increases in encephalization occurred only after the appearance of
> early Homo. The hypothesis that ER evolved in Homo for scavenging or
> even hunting therefore suggests that ER may have made possible a diet
> rich in fats and proteins thought to account for the unique human
> combination of large bodies, small guts, big brains and small teeth.
> --------
> Correspondence and requests for materials should be addressed to
> D.M.B. (bramble@xxxxxxxxxxxxxxxxxxx) or D.E.L. (danlieb@xxxxxxxxxxxxxxx).
>
>
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