Re: Chimp/Human Lines And Bipedalism


First published in Aug. 2002

curtad...@xxxxxxx (CurtAdams) wrote in message
<news:20020821024126.02305.00001906@xxxxxxxxxxxxx>...
jimmcg...@xxxxxxxxx writes:
curtad...@xxxxxxx (CurtAdams) wrote
The Sahel (the savanna just south of the Sahara) is the focal
point of human diversity. This indicates that that savanna

It wasn't a savanna back then. It had a much more significant rainy
season. It had much more extensive forests, which is where our
ancestors resided.


Nope. Quite the reverse. Africa's quite a bit *drier* during
ice ages,



You obviously don't know what you're talking about. We now have a lot
more data on the climate going back 10mya than we did even 5 years
ago. For example, did you know that the current drier savanna only
appeared about 2.x mya in Africa. For more detail see the following.

**********
In the interval between 4 mya and 3 mya the climate
took another shift back to a warmer wetter period
similar to the early to mid miocene. "The peak phases
of warmth during the Pliocene were mostly during the
interval between 3 and 4 million years ago (the
mid-Pliocene), although almost all of the Pliocene was
warmer than today's world."


http://www.esd.ornl.gov/projects/qen/pliocene.html


The late miocene and early pliocene (4 to 6 mya) was
cooler (and presumably drier and more seasonal) than
the above mentioned mid-Pliocene. But certainly not
as cool and dry as the last 3my. Thus the habitat that
produced the transition of apes to hominids--seasonal,
patchy, forested, with numerous lakes, streams, rivers,
and other sources of perrenial water--that existed from
about 6mya up to about 2.8 mya (possibly returning to
more or less of a rainforest in the interval between 4.0
mya and 3.0 mya) has largely disappeared in Africa
over the last 2.8 million years.


On a grander scale the determining factors of
seasonality have to do with things such as the level of
Co2 in the atmosphere, the flow of ocean currents.
The occurrence of significant winters (and eventually
glaciation) in the southern and northern extremities.
The abridgement of North and South America may
have had the most significant effect in that it shut off the
flow of equatorial waters that otherwise would flood the
coast of northern Africa. This seems to have occurred
during the late Miocene--about 5 million years ago.


The proximate mechanism of this seasonal dessication
is well known. It can most directly be attributed to
increased albedo (reflection of sunlight out of the
atmosphere) as a result of snow remaining unmelted on
the surface of landmasses at these northern and
southern extremities during the low sun months (winter
in the northern hemisphere; summer in the southern
hemisphere). This produces cooler ocean waters in
the northern and southern extremities. Ocean currents
are the transport mechanism that brings these
significantly cooler waters from the northern and
southern extremities to the western coast of Africa
which significantly reduces the amount of evaporation,
thus resulting in seasonal dessication to any regions to
the east of these cold water zones. (Note: since ocean
currents are not the fastest transport system we might
expect there to be a lag such that the actual season of
dessication would have been toward the latter part of
the low sun months [late winter, early autumn for the
northern hemisphere; late summer, early august in the
southern hemisphere]).


Jim
jimmcg...@xxxxxxxxx


The following passages are not my words. They were
cut and pasted from the links that follow:


During the late Miocene, the diversity of large apes began to decline
as
tropical and subtropical habitats of Europe and Asia began to contract
and
become concentrated closer to the equator.


At the end of the cenozoic epoch we see yet another cooling event,
related
to the expansion of the ice *** that covered Antarctica. Ocean
levels
dropped in response to the formation of ice on land, which resulted
repeatedly in the drying and catastrophic refilling of the
Mediterranean
Sea.


http://www.mnh.si.edu/anthro/humanorigins/faq/gt/cenozoic/miocene.htm


7. World-wide drop in sea level in late Miocene (6
mya)-->Atlantic-Mediterranean channel pinched off, Mediterranean basin
dries
up (refilled 3-2 mya); glaciation begins in Southern Hemisphere


http://oak.cats.ohiou.edu/~ballardh/pbio475/Diversification/Diversifi....
htm


By the mid-late Miocene the climate started to dry as highlands formed
becoming increasingly seasonal with fragmented forest areas.


http://www.arts.auckland.ac.nz/ant/201/anth201-6.htm


Jacobs, B.F., and Deino, A., 1996, Test of climate-leaf physiognomy
regression models, their application to two Miocene floras from Kenya,
and
40Ar/39Ar dating of the Late Miocene Kapturo site, Palaeogeography,
Palaeoclimatology, palaeoecology.123(1):259-271.


Jacbos, B.F., Estimation of rainfall variables from leaf characters in
tropical Africa, Palaeo3, in review.


Jacobs, B.F., Kingston, J., and Jacobs, L.L., Origin of
grass-dominated
ecosystems. Conference Proceedings, The origin of modern terrestrial
ecosystems: fossils, phylogeny and biogeography, Special issue, Annals
of
the Missouri Botanical Garden, in manuscript.


http://www.geology.smu.edu/~vineyard/bjacobs.html


These are the first quantitative estimates of climate for the Miocene
of
East Africa. The seasonally dry climate inferred for Waril may
indicate that
the Asian monsoon was established by about 9-10 Ma. Alternatively, the
seasonally dry climate may reflect local topographic changes caused by
rift
valley development. However, the plant localities suggest that,
although
progressive drying may have been a trend during the Tertiray, there
was not
a unidirectional change from forested to open environments in the
Kenya rift
between 12.6 and 6.8 Ma, the time interval just prior to the origin of
hominids.


http://www2.smu.edu/statistics/Jacobs%20Abstract.htm


If not ancient, then when (and why) did the diversity evolve?


Summer drought the key factor.


Circum-polar Antarctic current evolved in (late?) Miocene - spin-off
the
Benguela cold current.


Upwelling triggered by Benguela creates stable summer conditions and a
fire
climate in late dry season.


Demise of the forest communities results.


http://www.google.com/search?q=cache:90lPmKqSy-4C:www.egs.uct.ac.za/c...
egs314/lect14-1.ppt+late+Miocene+africa+seasonal&hl=en&start=7&ie=ISO-8859-­1


the Miocene hominoids (Miocene apes)
- Kenyapithecus, Oreopithecus, Dryopithecus, Sivapithecus, etc.
- general trend seems to have been towards more chewing -- eating
harder or
more fibrous foods
- presumably in response to the drying, more seasonal climate
- which would have encouraged woodier, tougher plants compared to the
tropical rainforest


http://www.google.com/search?q=cache:P8gRqIOpDgUC:members.aol.com/ant...
101s13.doc+late+Miocene+africa+seasonal&hl=en&start=37&ie=ISO-8859-1


**********


I think most theorist get too lost in trying to pick out which of
three
habitats, savanna, forest, or water, our species first began to
evolve.
Instead they should concentrate on a more explicit understanding of
the
habitat that we know did exist at the time hominids emerged.


Accordingly, up until about 6mya the whole of Africa was closed canopy
rainforest. Then starting about 6mya a new elements started showing
up,
seasonal dessication. (At the end of this post I have pasted another
post,
entitled The Late Miocene Origins of Seasonal Dessication in Africa,
wherein
I discuss the environmental and climatic factors that produced the
seasonal
dessication that emerged on our planet. [It is an element that had not
existed on this planet up until this time.]) This resulted in a very
dramatic dry season with some very unique implications.


Before I touch upon these unique implications it's important that it
be
understood how distinctively different was this habitat. Currently
there
exists nothing like it on this planet. In terms of moisture it was
like a
rainforest habitat for part of the year, and a desert the rest of the
year.
The rainforest itself would have largely disappeared having been
replaced by
patches of forest that persisted near sources of perrenial
water--streams,
rivers, lakes, ponds, etc. Our ancestors, of course, would have
inhabited
these well watered, still treed, localities in the greater
environment.


One implication of this new habitat would have been the seasonal
influx of
multiple species into these well watered, still treed, localities
during the
dry season (kind of a larger version of the watering hole phenomena
that
still continues on the african savanna). How would such have appeared
from
the perspective of our earliest chimpanzee-like ancestors? During the
rainy
part of the years they resided in a veritable garden of eden. Then,
during
the dry season not only would their sources of food begin to become
more
scarce but suddenly there comes an influx of other animals, refugees
of
widespread dessication, including other bands of chimps.


What adaptations might we expect to arise in our chimpanzee-like
ancestors
given the implications of this annual influx? I contend that one of
the
adaptations would have involved a networked (communicative) type of
territorialism, a kind of communal territorialism that would have
effected
the preservation of communal resources so that our earliest ancestors
that
produced this networked communal territorialism. It might have been a
peculiarly effective kind of territorialism in that it might have
enabled
our ancestors to effectively surround or circumscribe these well
watered,
still treed, localities, and thereby effect the preservation of the
resources at these locations and thus facilitate their own survival
through
the dry season.


Could our earliest ancestors have effected the communal territorialism
that
would have preserved the resources in these well watered, still treed,
localities? And if they did how would the selective benefits of this
activity--the benefits being the ability to survive through periods of
seasonal dessication--be focussed primarily upon those that produced
the
behavior rather than those that don't? In order to answer these
questions
it's important to be aware of what a serious selective factor this
seasonally recurring dessication would have been. It was a true grim
reaper. Those that for whatever reason did not have access to
resources
during the dry season died of starvation, thirst, as well as general
vulnerability to other factors, such as predators. These grim
realities, I
contend, make it clear that those that lacked some concept of the
value of
undepleted territory would be the first victims of seasonal
dessication and
those that survived would have been those that came to set up property
claims and defend them. Accordingly, I theorize that--in a manner
similar
to that of extant chimps--bands of our chimpanzee-like ancestors would
have
divied up the acreage of these well watered, still treed, localities.
These
property claims became the domain of the individual bands and also set
the
stage for continual conflict and sometimes cooperation between them.


But how did community consciousness emerge? It might seem obvious
that if
the sum effect of their territorialistic behaviors could reduce the
seasonally dessication inspired influx of other species by even 10%
that
this would be a tremendous advantage in light of the fact that other
well
watered, still treed, localities would now have 10% more influx to
deal
with. Accordingly, community sites that were occupied by bands that
displayed such behavior might thrive and come to colonize (and
disenfranchise) community sites occupied by bands that don't display
such
behavior. Over thousands of years we might, therby, envision all
community
sites becoming occupied by such communally territorialistic animals.
But
this still leaves open the question as to how an animal that was
capable of
defending it's own bands territorial claims could also come to evolve
the
ability to come to the assistance of other neighboring bands in the
same
community when these claims were challenged by those external to the
community (including other bands of chimps)? Are there theoretical
obstacles (ie. Darwinism) to the supposition that the selective
benefits of
such cooperative behavior would be focussed on those that perform this
activity rather than those that don't? It seems it would involve
selection
at the level of the community. And doesn't Darwinism tell us that
selection
at the level of the community is not possible? Or might there be
aspects of
this habitat--specifically the geographic isolation of these well
watered,
still treed, community sites--that allow us to overcome or dismiss
such
theoretical obstacles? And what other adaptations would we expect to
emerge
for an animal that begins to be selected for its communally oriented
territorialistic abilities. Might we expect the emergence of
adaptations
that would facilitate informational precision so that the members of
one's
commununity can better decide what actions are called for? And might
we,
therefore, also expect the emergence of adaptations that facilitate
communicativeness over long distances. And might bipedalism be such
an
adaptation by way of employing the body as a means of conveying
emotional
and information rich messages? Might bipedalism also be advantageous
in the
context of this scenario by way of enabling a collective rock throwing
behavior that would be effective in dissuading potential trespassers?


I think we can understand the emergence of humans from chimps. But
first we
have to start with an explicit understanding of their habitat and the
implications thereof that could have facilitated this emergence.


**********



Vignaud et al write of the section in which the hominid was found (p
153 para 1) ... "This water circulation between dunes represents the
first manifestation of a northward lake transgression, which
implicates episodic flooding and draining in a desert environment. The
anthrocotheriid unit (their name for the section) corresponds to a
shallow perilacustrine environment, subject to frequent inundation due
to to recurrent lateral excursions of the shoreline. For the present
day Lake Chad, such excursions may reach several tens of kilometres
over one or two decades. In this vegetated perilacustrine belt,
numerous environments coexists, from aquatic habitats in the lake and
along the shore, to very dry situations on the edge of the desert. The
wide variation in paleocurrent direction suggests the interdigitation
and coexistence of lacustrine, perilacustrine and desert
environments."


<snip>

. . . we'd be better off
bringing together all of the environmental factors indicated above in
Vignaud et al to try to paint a more comprehensive picture of the
environment/habitat. Toward that end:


From what is stated in Vignaud et al the following seem apparent to
me:
1) The environment/habitat was much wetter than it is currently:
This seems evident based the the observation that the lake was
much
larger (how much larger?) than it is currently.
2) The climate was highly variable with respect to precipitation
This seems evident based on the observation that, firstly,
the size
of the lake seems to have fluctuated: "This water circulation between
dunes
represents the first manifestation of a northward lake transgression,
which
implicates episodic flooding and draining in a desert environment."
Secondly, precipitational variation seems evident based on the
observation
that a treeless "desert" habatit existed nearby. Given the high
overall
wetness of this environment/habitat (as indicated in #1), this last
mentioned observation can, I contend, only be explained by the
existence of
extended and severe dessication as a factor in the climate. If this
was not
the case then this "nearby" desert could only have been forested.
Putting
1) and 2) together, I contend that the best way to describe this
climatic
variation is with respect to alternating between periods of high
rainfall
and periods of little or no rainfall.


Next we can ask ourselves how we can more precisely describe the
periodicity
of the above theorized climatic variation in precipitation. Although
the
possibility exists that this climatic periodicity could have been
dictated
by global changes that themselves might be best characterized by
changes in
rates of advancing or retreating glaciation, I think this is unlikely.
The
timescale of this kind of fluctuation is either too long, on the scale
of
thousands of years, or too short, one to ten years (as when triggered
by
geologically catastrophic events, meteor impacts, volcanoes, and
resulting
nuclear winters). The gradualness of the first leaves us unable to
explain
the close proximity of desert habitat. The brevity of the second
makes it
too improbable that we would just happen to find fossils of such a
narro
slice of geologic history. Given these assumptions (the validity of
which
will, to some degree, depend on the degree the above mentioned
description
in Vignaud et al represents a snapshot in time or a longer duration) I
think
it's more likely that the "episodic" element indicated in Vignaud et
al is
seasonal. Putting it all together, I think the environment/habitat
can be
described as having been different than it is currently, maybe even
dramatically different, in that it contained a distinct and very wet
rainy
season. But, I suspect, it was also similar to the environment that
we find
currently in Toros-Menalla in that it also contained a distinct and
very
severe dry season. More to the point, the climate may not have been
unlike
the monsoon climate that we currently find in India or, possibly, a
more
extreme version thereof.


With this picture of a monsoon-like environment/habitat in mind, I
don't
think there is any reason to imagine our ancestors either being "on
the
savanna" as suggested by Rich or "wading" as suggested by Algis. I
think it
is pretty obvious where our earliest ancestors resided. They were
"perilacustrine" (which I think translates from latin as, "close to
lake.")
And I think it's pretty obvious why they were close to the lake (or
close to
any similar source of perennial water: ponds, springs, streams, or
even
sources of high ground water), this is where the trees were.


These were chimps. And as such an open and relatively treeless
savanna
holds no potential for them. Nor does a desert. Nor does anything
much
closer than 50 feet from incessantly crocodile infested waters. Their
niche
in the greater habitat was well defined by the momentum of millions of
years
of evolution. And although their preferred habitat could be said to
have
been under assault for the last 2 to 4 million years as the global
climate
shifted to being cooler, drier and more seasonal, their habitat had
not
completely disappeared. Patches of their wooded habitat still existed
at
these "vegetated perilacustrine belts," and other similar belts of
vegetation near rivers, streams, ponds, and other sources of perennial
water. But there was a caveat, the environment now contained a
significant
left hook, this being seasonal dessication, an element which must have
been
the source of considerable hardship for any and all of the once
exclusively
rainforest dwelling species that now co-occupied these perilacustrine
sites.


An element introduced in this last sentence above--other
species--brings to
mind a question that I've been harboring for a couple of months.
Because
they were so completely dependent on the existence of forested habitat
our
ancestors had little or no choice but to reside in these "vegetated
perilacustrine belts," at all times of the year. But the same would
not
have been true, or as true, for many of the other species therein.
Especially not for those species to whom for which trees were little
more
than a nuisance. They may have only needed to be "close to the lake"
during
the dry season. This indicates multi-species migration toward these
well-watered locations during the dry season and back out again with
the
onset of the rainy season. Now here's the question: does anybody know
if
any scientists/researchers have done any theoretical thinking,
investigating, and/or hypothesizing on the implications of seasonal
inmigration/outmigration by multiple species at these forested,
perilacustrine locations? Specifically, I'm wondering about any such
implications in the context of scenarios on the earliest years of
hominid
evolution.


**********


which cover most of the time of sapiens habitation.



So much so that the rainforest shrink to small refuges.
The Sahel was wetter from about 10 kya to about 1 kya
but that's not much compared to 100 - 10 kya and it wasn't
forest even then.


Get your facts straight.

Jim



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