Spearthrower wrote:zoon wrote: You say there is a situation where “afarensis are employing tools which already suit their morphology reasonably well”, and appear to be dismissing the possibility that a mutation may arise which enables them to employ those same tools a little better?
Employing the same tools a little better doesn't mean it helps them employ other entirely different tools. I'm afraid this is another one of JJ's misleading ideas that might have snuck under your radar; it might be useful to consider tool use as an abstract in comparative terms between species, but tools are not abstract, they have very specific functions and very particular uses which don't automatically translate to other functions or other uses. I've made it clear already that expanding tool use versatility, and particularly tool manufacture, is predominantly cognitive, not anatomical. So I think it's worth remembering the Hopeful Monster notion where multiple mutations all need to occur concurrently in order to get the desired notional 'adaptation'.
zoon wrote: Such a mutation would be selected for, and after a few such mutations are fixed in the population, and after a few such mutations are fixed in the population,...
For me, that doesn't stand to reason. How much of a selection pressure is there on that particular tool use?
Take those chimpanzees cracking nuts. How many chimpanzees actually crack nuts in that manner? How often do they use that kind of tool to crack a nut? How much of their routine nutrition do they get from cracking nuts? How much actual benefit in nut-cracking can a notional mutation offer? Does that mutation carry any other costs associated with it?
Even more obviously beneficial mutations don't automatically become fixed; there needs to be strong selective pressure to drive an adaptation to fixity.
zoon wrote: the possibility of using a new tool with the new morphology might arise?
Like I said: it's an abstracted tool.
Let's imagine my population gets continually adapts over generations to get better at smacking nuts with a hand-axe stone, how did this eventually offer me any benefit in using a completely different tool in a completely different manner?
It might let me use a similar tool in a similar manner, but then why couldn't my population already do that?
A different tool in a different manner is not something that is innovated by anatomy, but by cognition.
zoon wrote: Isn’t this the way natural selection works, for any trait?
I am not a strong adaptationist. This is a massive discussion that wouldn't be easy to do justice even if we had a thread specifically focused on it and time to delve into it deeply.
If you'd like to read up on the opposite position - which I am not saying I am firmly encamped in - then you'll find this paper gives you a great foundation:
https://faculty.washington.edu/lynnhank ... wontin.pdfThe Spandrels of San Marco and the Panglossian Paradigm: A Critique of the Adaptationist Programme. Gould & Lewontin, 1979
To answer your question though: the usage of the word 'trait' is problematic. If by 'trait' you mean an adaptation, then yes of course that trait has been selected for... that's kind of definitional, but traits aren't all adaptive - most traits are highly variable in any given population, so it's hard to see how they could
all be adaptive yet also be
mutually exclusive. There are plenty of tools and techniques employed for determining whether a given trait is adaptive or not, but we're moving outside my ability to talk knowledgeably about it and I can only refer you to discussion papers. I studied Human Evolution, not Evolutionary Biology.
zoon wrote: You say “there's no innovation in tool manufacture or usage in most species, afarensis included”, but presumably at some point a sub-population of afarensis evolved into africanus, which has a different hand and wrist morphology (if I’ve understood your post
#4214, requoted in
#4235), better suited to manipulation, is this not innovation?
Woof... there's a lot to unpack in there!
First, let me just nitpick something: there is no 'point' at which X population evolves into Y population except in a Platonic taxonomic sense: in reality, there's a chaotic mess of DNA representing a pool of a wider population, some of that pool is being pulled one way, some may be being pulled another way, but traits are aggregates. Assuming africanus evolved from afarensis, then there'd be an as-yet undiscovered intermediary possessing some of the traits associated with africanus retained among traits possessed by afarensis... but that individual fossil would represent only a single snapshot of a wider population possessing variable traits.
Second, to go back to an earlier point, I think it's vital to remember that there are ways particular anatomy can be employed and many types of tools and means of using those tools, so a given range of functions might (through grip and precision) open up the ability to use old tools in better ways, use old tools in new ways, or use completely new tools, but that doesn't mean any of them are automatically going to be used in any of those ways - it certainly doesn't mean that the tools need to 'evolve'. For me, the missing ingredient here is the cognitive aspect of tool use - it's not just hand anatomy, or wrists, or bipedality... there's a fundamental cognitive component here that can't be overlooked while focusing solely on morphology.
Thirdly, I refer back again to the problems of adaptationism. How much benefit accrues from a given trait being selected for to become adaptive? I think the use of any particular anatomical feature has to be considered holistically. A hand isn't just being used to hold a branch and therefore climb a tree, it is also being used to pick a fruit, to peel spines off of it, to break that fruit into manageable pieces, to carry that fruit, to place that fruit into the mouth... the hand is also being used to groom one's fellows and oneself, to grab insects etc. etc.... in short, to perform a range of functions, all of which may be presenting competing selective pressures as particular anatomy may be preferable one way for one function, but another for another use. So then we'd perhaps need to look at which is offering the most survival benefit, if the trait is meant to be seen as adaptive. Which is the most important for the possessor of it to succeed in passing its DNA onto the next generation. I think what we would typically expect is some kind of Frankenstein - a hand suited to all of them, but not specialized in any to the detriment of the others. Across a population, the variability here may mean some individuals are better at peeling while others are better at smashing and others are peerless climbers, but a constrained range of anatomy has to support all these mild specializations.
Finally, I think to really dig in here, we need to look very closely at the technology being discussed because I think it's not necessarily the case that everyone's familiar with it. For example, I've already pointed out that chimpanzees can accidentally create flakes while bashing hammer and anvil stones. Chimps can then also use those flakes for other purposes. This isn't quite as sophisticated as Oldowan technology, but it is very close - Oldowan industry is extremely crude, and it doesn't change for a million years; there are perfectly respectable arguments made that it is cognitively equivalent to the haphazard, unplanned results of chimps bashing rocks, that Oldowan as a method is basically ex tempore fortune and really not a manufacturing process at all. Acheulean technology is a little more sophisticated, but then again doesn't change for a million years. There is no apparent innovation occurring here - the techniques stay largely the same across vast tracts of the world for hundreds of thousands of years. So again, we're not seeing innovation - that comes later with Mode III tools which are clearly superior versions of Mode II - they're obviously worked, they are obviously planned, and they are obviously innovations, and consequently we see massive variability in tools and tool use explode at this point.
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