Re: Faithful Ancestors was Re: Doesn't ANYONE have anything new to say?

rmacfarl wrote: 

Lorenzo L. Love wrote:

rmacfarl wrote:

...
"Plavcan and his colleagues determined the relationship between various

skeletal measures and body mass for 658 people from eight populations
in
different parts of the world. With those correlations, the team made
new
calculations of femur-head size and body mass for seven A. afarensis
specimens not in the First Family and assigned sex on the basis of
size.

This work reveals sex differences considerably greater than those in
people and approaching those in gorillas, according to Plavcan's team."


"and assigned sex on the basis of size."
That's the same circular reasoning McHenry used, Plavcan just confuses
the matter by using femur-head size instead of overall size. It's still
separating the bones into two piles based on size, arbitrarily assigning
the big bones as male and the little bones as female. All you really
have is two piles of bones, sex unknown. Maybe most of the big bones are
male but there's likely to be a few Gabriele Reese in there and maybe
most of the little bones are female but there's likely to be a few Danny
DeVitos in there. Every misidentified bone inflates the dimorphism amount.



Firstly, I don't understand how you deduce from the article that
Lovejoy's methodology was any less arbitrary than Plavcan's or
McHenry's.

Secondly, Gabriel Reeses or Lauren Jacksons (a plug for the Aussies if
we're talking giant wimmin who "got game"), or Danny DeVitos, don't
appear once in every 22 individuals.

Thirdly, in nature pathological giants & midgets generally have poor
survival &/or reproductive success, all else being equal.

We're not talking about pathological conditions, just the outside edges of the bell curve. It only takes one misidentification to throw the results off. Note Plavcan only used seven specimens.


Does any one know: is there a reasonably clear distinction between the
large & small fossils? Jason - any comments?


The proper methodology would be to determine sex first by indisputable
anatomical structure, not gross size, then measure the comparative sizes
of the two sexes. Disregard any bones who sex can not be determined
without regard to size. That's not going to happen because there just
isn't enough intact pelvises around. There is still disagreement over
Lucy's sex because her's or his pelvis was so badly busted up. The
assumption is she's female because she's so small, but it's just an
assumption not a fact.



...

An orangutan can only monopolize one female at a time. One after another
maybe if he's got the stuff, but just one at a time. A gorilla, in
theory, can monopolize several females at once. And so very different
social structures in spite of similar levels of dimorphism. Chimpanzees
and bonobos as you note have different social structures but similar
levels of dimorphism. So what does dimorphism tell us about social
structures? Not a lot.



Not so. It's been a while since I read Birute Galdikas, but as I
recall, what the big orang males do is monopolise the best bits of
forest, & specifically the best fruiting trees. They do use size to
keep the rival males away, they do attract a disproportionate
percentage of females, and they do attract a highly disproportionate
percentage of successful matings.

No matter how big an orangutan's territory is, they don't form harems but go from one isolated female to another. One at a time.


Sexual dimorphism between males & females is no accident. In most
vertebrates, & as far as I know all primates, males are bigger than
females, and there is a correlation between the degree of dimorphism
and the level of competition between males for reproductive success. It
tells us a lot.
...

It tells us zip about social and sexual behavior as the similar dimorphism between gorilla and orangutans and the very different social and sexual behavior shows us.



Occam's razor tells me that when you have 2 great apes who are
morphologically as similar, with lifestyles as radically different, as
chimps & bonobos, you postulate early hominids' behaviour at your
peril...


...

That's right, behavior is so fluid and changeable, especially sexual and
social behavior that it will probably alway be a mystery but physical
characteristics like dimorphism can be determined with sufficient data
(which we don't have yet). It just won't tell us much about behavior.

Meanwhile Occam's Razor tells us the default assumption should be that
afarensis probably had similar levels of dimorphism that the species
most closely related to them have. McHenry and Plavcan's contorted
analysis not withstanding.



Considering how close temporally the split between Pan & Gorilla is to
Pan / Homo, and how far either is temporally from Lucy, Occam's Razor
ought to tell us that the default assumption or the null hypothesis is
too close to call. Pan & Gorilla evolved in different directions
socially & morphologically, & P troglodytes & P paniscus in different
directions socially, within the same time timespan. The odds of the
LCA, or any individual species of Australopithecus, showing high or low
dimorphism are darn-near equal on my reading.

The First Family is (probably) a rare case of a statistically
significant sample size of a single species at a single moment in time.
It ought to tell us much more than Occam on this occasion. It's just
that you & I, & Lovejoy & Plavcan, aren't reaching the same conclusions
from the same data set.

Note that Plavcan didn't like the data he got from the First Family so he threw them out and used other specimens. Not from a single moment in time and only seven individuals.


And somehow I suspect that it is much more likely to be Lovejoy or
Plavcan, or some of their proteges, who are much more likely to resolve
this question clearly one way or the other, than either of us are.

Which shouldn't, however, inhibit us in any way from arguing about
it... :-)

Ross Macfarlane


Lorenzo L. Love
http://home.thegrid.net/~lllove

“Facts are meaningless. You can use facts to prove anything remotely true.”
                            Homer Simpson


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