Re: A critique of the BBC aquatic ape programme and the transcript.



JAE wrote:
> Algis Kuliukas wrote:
>
>
> > So, having exposed my error, Jason, can you now explain to me why drift
> > is the best explantion for humans' relatively superior swimming
> > compared to chimps but not our walking efficiency and not chimps'
> > greater climbing and hand-to-hand fighting abilities? If you can, then
> > I'll happily doff my cap to you and eat an even bigger slice of humble
> > pie than I'm choking on now.

Well. I'm certainly doffing my cap to you after this, Jason, but I'm
not quite ready for more pie! Thanks, also, for resisting the easy
target of gloating at my error here. Much credit to you for that too.

> I think the best way to think about this is not to try to say "drift
> explains it" or "selection explains it" because indeed in isolation,
> neither statement is going to be wholly true nor sophisticated enough
> to have much meaning on its own.

Fair enough.

> To show what I mean, I'm going to use something that we understand
> better, the "climbing" as you've put it which, in this sense seems to
> involve a whole lot of things, but things that we've got a better
> handle on than either bipedal locomotion or swimming. This is true for
> a number of reasons: there are more climbing animals than there are
> bipeds; we have a much better idea of what features make for a good
> climber as a result and have a longer fossil trail indicating climbing
> primates going way, way back while our form of bipedalism is a recent
> advent, confined today to one lineage and without good analogs to work
> with. Swimming involves another problem--more later.
>
> The short answer as to why chimps can climb is more or less because
> gibbons can climb, macaques can climb, cebus monkeys can climb, and
> lemurs can climb. Chimps have a number of anatomical features that
> make them better at climbing than we are. They've got opposable big
> toes, though this is a primitive feature. They've got longer, curved
> digits, though again, this is a primitive feature. They share with us
> the brachiationist's shoulder and arm, again a primitive feature that
> is coupled with greater musculature, again, seemingly a primitive
> feature. More or less all of what makes a chimp a better climber was
> most likely present in the last common ancestor of chimps and humans.
> It isn't something that selection "gave" chimps since the split. It's
> more indicative of what we lost. I don't think your simple "selection"
> answer appreciates this distinction, though it's terribly important.

This all makes perfect sense.

> Why we don't have these features is almost certainly a complex
> combination of selection for other features (e.g. the adducted big toe
> that makes our foot a better balancine lever to walk with) and drift
> eliminating traits that aren't under strong enough selection to make
> sure they are maintained. Relax or remove selection and evolution
> proceeds but in a manner difficult to predict and sometimes difficult
> to make sense of when you look at anatomical traits. I suspect some of
> our reduced upper body strength was part of this once better tools and
> a more terrestrial existance made it superfluous. Possibly, it was
> somehow more "expensive" to maintain, though this isn't by any stretch
> necessary.
>
> Could we be effective bipeds and still have the curved phalanges and
> greater musculature? Apparently so because the earliest bipeds showed
> this pattern. But when we didn't need these features, they began to
> disappear as is absolutely predicted though random drift, no NEED to
> invoke selection, something that's dreadfully difficult to actually
> demonstrate in this case.

Now this is where I may need a little more help. To my, perhaps naive,
mind when drift removes features because they are no longer "needed"
and therefore not positively selected *for*, isn't it short-hand to say
they were 'selected against'? Isn't *lack* of selection 'for', exposing
it to the erosion of drift, still 'selection'?

> [Could we be effective climbers with our
> feet? Possibly, as those modern cultures who rely on climbing to get
> resources seem to do quite well at it. It's tough to really say how
> much of an impediment this would be to an otherwise chimp-like body,
> but I'm inclined to think that this change for bipedalism probably made
> climbing somewhat less efficient while making terrestrial movement
> somewhat more profitable and this change in lifestyle allowed the rest
> to start to fade away without selective consequence one way or
> another.]

> Consider this: Chimps climb better than us, but they don't climb as
> well as orangs or gibbons. If there's a better climbing common ancestor
> of all apes (likely given the fossil record and the comparative
> outgroups among old world monkeys) what seems to have happened is that
> our lineage lost climbing abilities both before and after the split
> with chimps. We just lost more because we prospered without it. Once
> the split happened, chimps stopped losing abilities (or were losing
> them slower than we were) because selection wasn't relaxed as much as
> it was for us. This is very different than selection favoring the gain
> of an ability.

Jason, from where I'm standing saying "selection wasn't relaxed as much
[in chimps] as it was for us" is still saying that "selection did it."
I'm not wedded to the idea that selection has to be positive. Removed
negative selection is still some kind of selection.

> Which brings us to swimming since it seems to be what you argue when
> you talk about swimming--it was something we gained, some sort of
> selection FOR the ability.

Not necessarily. Less selection aginst, is still selection in my book.

> To actually look at this, we need a starting point. Whether or not we
> can swim better than chimps *isn't* the only comparison that matters if
> you want to talk about how selection shaped our particular form and you
> are arguing that swimming was responsible for X, Y or Z. There's the
> possibility that the traits we have that allow us to learn to swim as
> proficiently as some of us do are related to other causes. The full
> mobility of our shoulder that allows for the Australian/Polynesian
> crawl is something we share with all apes and is clearly related to a
> brachiationist ancestor. Arguing that it's a result of swimming--not
> saying you did this, but if you did--isn't necessary because the trait
> has another use that much better explains it and explains why we see it
> in gibbons, orangs, and the African apes, none of whom seem to swim
> this way.

Ok, so we could be better swimmers by proxy of other traits which were
selected for other things. Ok. That's possible.

> We DON'T know if the LCA could swim, but I'd not be at all surprised if
> it could given that the majority of mammals can, that apparently, given
> the right incentives, chimps and gorillas can, gibbons can, and many
> many other primates can.

Now I must interject here. Gorillas can, agreed. Orang-utans,
apparently cannot. The evidence for Pan is almost (but not wholly)
totally 'cannot'. For Gibbons, it is more 'cannot' than 'can'. I think
you're stretching it a bit here. The Hominoid LCA would appear to be
less likely to swim than the LCA of all primates and the LCA of all
mammals. If you were right here, if there was better evidence that the
LCA of all hominoids could swim, I'd be much happier to agree with your
general argument.

> With some great questions about chimps and
> consequently the starting point from which we diverged, we've got to
> widen the field and when we do so, swimming seems to be much more often
> the rule whether or not the creatures practice it regularly. We don't
> know what sort of abilities this creature had to determine what was
> gained or lost in which lineage but it seems likely to me that if
> chimps don't swim well, it was because they lost something, not
> necessarily that we gained some ability through selection FOR that
> ability.

Ok. But no matter what the LCA could do, chimps diverged from humans in
terms of swimming ability. It make have been a positive gain in humans
or a negative loss in chimps, either way something changed in relative
swimming abilities. Drift alone can't explain that without the subtle,
but essential, addendum 'because it was no longer needed' in one.

> It's uncertain certainly. With this much uncertainty, we have to be
> careful and conservative with our hypotheses and we have to be mindful
> of the reality that drift is always working and as such, it's the null,
> it's what we have when we've got nothing else confirmed with which to
> reject the null.

But didn't you say yourself that drift is only expected to remove a
trait when it's not needed - hence not selected for?

> So we need to stick with what we can actually look for selection for
> and examine these things rather than the nebulous "we swim more" which
> DOESN'T explain much at all even if entirely true.

This is another area where I think you don't do the idea justice. "We
swim more", unlike "we walk more" and even unlike "we climb more" is
much more likely to result in death. The selection for such traits that
help swimming are likely therefore amplified.

> On its own it
> doesn't explain hairlessness (not that we're hairless and expecially
> not so given that there's already a trend towards less hair in some
> other apes). It doesn't explain breath control because it's not clear
> that this is something unique to us. We DON'T know that there was ever
> selection for "diving" but we're not the only primate to do this and
> the adoption of the behavior has been witnessed in macaques as a
> learned behavior that showed up quickly and got passed on to other
> monkeys who observed it.

I don't want to argue about all these points again here.

> It doesn't explain why some people can swim
> very far either as in general we're good endurance creatures and it's
> not clear that this is anything more complex than taking a generally
> favorable trait that could have been acquired for anything (like
> walking a long way) and applying it to something that we could already
> do (like swimming) without selection pairing the two for any particular
> survival ability.

That's a good point.

> Without strong reason to invoke swimming (e.g. strong evidence that it
> actually happened; that it was super-favorable to do so; that the
> analogy for a particular trait is strong enough to make us believe that
> water was the primary selective force--an analogy that can't be drawn
> without looking at creatures who actually swim, who are actually
> aquatic in their lifestyle and adaptations) swimming is superfluous.

I just don't agree with that. Why does it have to be
'super-favourable'? Why not only 'a bit favourable'? Surely if humans
were exposed to the risk of drowning more than chimps *at all* then
that would bve *enough* to have some effect, even to prevent some of
that drift.

> But the paricular evidence really isn't there yet by any stretch and it
> won't be there continuing to argue a generality like "we swim better."
> Since swimming isn't unusual in mammals at all--it tends to be the
> rule--without some clear indication that we evolved from a
> "couldn't-swimmer" that it's not something we gained, only something
> that we elaborated on given a form that was changing, but not
> necessarily changing *because* we needed to swim better--something that
> can't be established just because of the observation of the end point.

Again if we had better evidence for the LCA of the apes being good
swimmers I'd agree with this point. But AFAICS all but the gorillas are
non-swimmers and humans are even better than gorillas.

> If there was a big change such that chimps have a limited ability (not
> willingness, but ability--again something that isn't clear) to swim, it
> could well have been the chimps who changed and there's no need to
> invoke selection here. Take a creature out of water long enough and
> the ability can disappear by drift without needing to invoke selection.

Again this appears to me to be 'selection-by-stealth' rather than drift
per se.

> There may or may not have been selection for us to maintain the
> ability. Perhaps. It doesn't seem expensive for a terrestrial to have
> some abilities in the water so there doesn't need to be much selection
> to favor keeping it. It's so widespread that I suspect that in most
> creatures there's a widespread, slight pressure to maintain the
> ability. If this is what you mean by "water influenced us more than it
> did chimps" then it's entirely plausible, but it's also entirely boring
> and damn near entirely useless in explaining our phenotype, our
> behaviors, our lifestyle since the divergence with the LCA.

Great! I agree, it *is* entirely boring... but I don't agree that it's
necessarily useless in explaining the human condition. I think we
overestimate how much selection is required to make profound effects.
Just look at the skin colour of humans and how it's, presumably,
changed so markedly from the LCA condition in less than 200ky. Just a
little more xposure to skin cancer - it stays dark, just a little less
Vit-D production and it goes light.

> The changes in our lineage don't need to be explained by swimming and
> most clearly have solid explanations that do the job on their own.
> There's no need to invoke paddle feet to explain rather ineffective (by
> any real aquatic standard)) paddles when selection for them as the
> balancing lever for a bipedal stride wholly accomplishes the task and
> we know that the creatures walked bipedally because it's our primary
> means of getting around still. The parsimonious reasoning here is to
> not invoke two causes when you only need one. The aquatic cause is
> the superfluous one since we're not terribly aquatic and the traits
> have to function on land first and foremost since this is where we live
> first and foremost. There's no need to invoke swimming for our
> "linear" build if similarly this build is explained again as an
> adaptation to a more effective bipedal gait for a creature with
> expanding home and day ranges who traveled farther and showed greater
> energetic efficiency and endurance than other creatures, something that
> appears to be true in us, swim or no swim.

Look, I agree with much of that but I think it's a bit binary. I'm not
saying there was exclusive aquatic pressures and no other. The fact
that we can swim better than chimps simply makes me think that whatever
went on in the last 5-7my since the LCA probably involved some mild
pressure for swimming, that's all.

> The short answer is that drift may not be the answer and it's not a
> terribly satisfying one either, but the onus on ANY adaptationist
> explanation is to explain the adaptation. It isn't the null and it's
> especially not the null when we consider moving both towards a trait
> and away from a trait.

So do I take it that your answer to my question was...

Climbing - largely selection.
Walking - largely selection.
Swimming - largely drift?

Algis Kuliukas

.

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