Re: Savanna mammals

Another savanna fanatic who thinks that become a few humans today run after
kudus out ancestors 2 Ma ran after kudus:


Op 21-01-2008 06:17, in artikel 47942AFD.9A3F6F37@xxxxxxxxxxxxxxx, Rich
Travsky <traRvEsky@xxxxxxxxxxxxxxx> schreef:

Marc Verhaegen wrote:
Op 14-01-2008 05:15, in artikel 478AE1CC.43B97BEC@xxxxxxxxxxxxxxx, Rich
Travsky <traRvEsky@xxxxxxxxxxxxxxx> schreef:
Marc Verhaegen wrote:
Op 31-12-2007 08:32, in artikel 47789AFF.AF2BAABC@xxxxxxxxxxxxxxx, Rch
Travsky <traRvEsky@xxxxxxxxxxxxxxx> schreef:

http://www.verticalblue.net/team.php

:D
"William descended to a depth of 82m on one breath of air, without
fins, weights or any other form of assistance."

So?

Kududs swim 82 m under water, you mean?

What are you babbling about? Kudu are on land where humans live.

My litte boy, nobody doubts we live on land.
Point is: were our ancestors 2 Ma kudu runners or waterside omnivores?
Think a bit:
- kudus are on land
- humans can dive tens of metres
Got it?

Being at the waterside doesn't mean you can dive. On the other hand:

Long distance running is one of the great skills of humans when compared to
other species. Although a horse is far faster in a sprint or a short gallop,
a well-trained human can outrun a horse if the distance to be traveled is
greater than 15 kilometers, or about 10 miles (Bramble 2004). Based on the
anatomy of fossils, the current thinking is that the capability for extended
running appears to be a relatively late development. Many features related to
this ability are seen in Homo habilis at 2.5 million years ago, and virtually
all of them are seen in Homo erectus at 1.8 million years ago...

I'm not interested in just-so opinions, I'm interested in serious arguments.
Bramble and Lieberman (2004), in a much-discussed review article in Nature,
cite a number of derived Homo features they claim to be adaptations for more
efficient endurance running in arid, open habitats. However, while some of
these supposedly ?cursorial adaptations¹ appear first in the fossil record
in H. habilis, others appear first in H. erectus, and others still in H.
sapiens, suggesting a much more complex story than proposed by Bramble and
Lieberman. Their conclusions are reached without systematic comparisons
with other animals (including endurance runners) and with general
comparisons restricted to fossil hominids and Pan. Since convergent traits
are strong indicators of evolution in similar environments (Bender 1999), a
systematic comparison with a broad range of animals with a variety of
locomotor strategies would have been more informative.
In addition, discussion of possible locomotion styles is restricted to
walking and running, with no consideration at all given to activities such
as wading, swimming or underwater foraging, yet humans are regular waders
and more accomplished swimmers and divers than other primates. Most of the
list¹s ?adaptations¹ for walking could just as easily be explained by
wading. One of the frequent ?explanations¹ in the list is ³stress
reduction², a reference to the vertical posture of humans with the weight
resting on two legs. But this says nothing about endurance running, with
standing, wading, walking or short distance running all using a similar
posture, and therefore all requiring stress reduction. Other ?explanations¹
include ³counter rotation², ³thermoregulation² and ³stabilization², but no
comparative data to corroborate these interpretations are provided. In
other words, their ?explanations¹ are ad hoc suppositions, applied to one
example (human ancestors) without any consideration as to whether these
supposed adaptations are seen in other animals, which means their
?explanations¹ are statistically invalid (n=1). Long legs, and possibly
shortened forearms, could be seen as running adaptations, but these are just
as typical of wading and swimming species compared with runners (Hildebrand
1974: 584, Bender 1999).
In a waterside scenario, wading and swimming would be preadaptative to the
humanlike ?vertical¹ locomotion that Bramble and Lieberman (2004) believe to
be a direct adaptation to endurance running. In our view, frequent
terrestrial locomotion, whether for walking or for (relatively slow)
running, was more recent (Homo sapiens) and could not be derived directly
from an ancestral locomotion in forests, whether on the ground or in the
branches, because in that case a more baboon-like locomotion would be
expected (the ?baboon paradox¹).
Most of Bramble and Lieberman¹s ?adaptations¹ are not what we would expect
in a cursorial (running) animal. For example, their list includes ³enlarged
posterior and anterior semicircular canals², but there are no comparisons
with, for instance, giraffes (heads high above the ground), gibbons (fast
and versatile locomotion), kangaroos (cursorial bipeds), or swimming or
diving species. It is conceivable in fact that the frequent change of
posture seen when diving for seafood (descending and ascending) required a
different labyrinth structure, and that the larger Homo erectus labyrinth
was adapted to terrestrial walking and running as well as to wading,
swimming and diving locomotions.
There is no indication that an ³expanded venous circulation of neurocranium²
had anything to do with thermoregulation, but there is long-standing
evidence of expanded venous networks in diving species (Slijper 1936).
More balanced heads and short snouts are not seen in cursorial species,
whether bi- or quadrupedal, and low shoulders are to be expected in wading
and underwater swimming.
What Bramble and Lieberman refer to as ³narrow body form², ³narrow thorax²
and ³narrow pelvis² is not clear to us: compared to most primates, humans
have a relatively broad thorax and pelvis (laterolaterally), and this was
even more so in the case of australopithecines. In our opinion, the
combination of ?flared¹ iliac blades and long and relatively horizontal
femoral necks as seen in Homo erectus indicates well-developed ad- and
abduction, which is obviously not an adaptation for running, but would not
be unexpected and indeed would be advantageous for a species that had to
regularly wade, tread water, swim or climb. In Homo sapiens the pelvis
(bi-iliac diameter) did become narrower and the femoral necks shorter and
more vertical, and we agree with Bramble and Lieberman that this could be
related to more frequent terrestrial locomotion.
Plantar arches, enlarged tubera calcanei, close-packed calcaneo-cuboid
joints and short toes are not seen in cursorials, whether bi- or quadruped,
to the contrary: running species are typically unguli- or digiti-, not
plantigrade, and typically have elongated toes.
In conclusion, comparative data suggest that none of the features described
by Bramble and Lieberman (2004) are typical either of savannah dwellers or
frequently running animals, whether slow or fast. Until the features are
considered in the context of swimming and wading as well as terrestrial
movement, their interpretations should be considered with extreme caution.
As it is, there is no obvious reason why any of the features cited could not
have been of advantage in a littoral environment. We do not deny that
humans today are adapted to terrestrial locomotion including walking and
moderate running, but in our opinion the peculiar human anatomy is not
directly derivable from a typical primate ancestor who moved from closed to
more open, arid habitats.


.

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