The evolution of bipedalism

[Gerrard Farrell]

Just wondered what people thought of the "ground up kinetic " theory of the origins of bipedalism . Basically, what I am saying in this thread on Podiatry Arena (below) is that bipedalism was selected for because of the enormous forces that a biped can develop in a hand held object , by a leg driven , uncoiling action of the body .

The evolution of bipedalism | Podiatry Arena

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Any thoughts ?

[Musa Audu]

Re: The evolution of bipedalism

An addition to the discussion will be the interesting and cogent issues raised by Prof. Latimer in his article "The Perils of Being Bipedal" which appeared in Annals of Biomedical Engineering, Vol. 33, No. 1, January 2005. pp. 3–6. Musa.

[Gerrard Farrell]

Re: The evolution of bipedalism

Hi Musa , many thanks for the note and reference . Professor Latimer does raise some interesting points in his article and for early bipedal apes there would have been many downsides to this phenotype and , in my opinion ,only one very distinct advantage ,tool use , and in particular , high energy kinetic energy tool use . No other animal can summate the forces produced by the entire body as well as we can ,and then deliver them into a hand held object . It defines us physically .

[Edmund Cramp]

Re: The evolution of bipedalism

Evolution is always so much clearer in retrospect - I wonder what the future holds for us?
human-evolution.jpg

[Drew Smith]

Re: The evolution of bipedalism

Great picture, Edmund, but I think the image on the right is wrong: it should be looking down at the smartphone in its hand, oblivious to the fact its about to fall off a cliff!

[Edmund Cramp]

Re: The evolution of bipedalism

Great picture, Edmund, but I think the image on the right is wrong: it should be looking down at the smartphone in its hand, oblivious to the fact its about to fall off a cliff!

Actually I was thinking more along the lines that the questions in this forum are often more interesting than the answers - which is not to say that the answers are not interesting, it's that the questions make me think much harder. I think that Gerrard makes an excellent argument, although I'm slightly skeptical that evolution is quite so directed ... maybe we evolved to bipedalism simply to escape being another animals lunch? If Gerrard is correct, where does the future lead us since his evolutionary thrust no longer exists in our modern world?

[Ross Miller]

Re: The evolution of bipedalism

My uninformed backseat-evolutionary-biologist opinion is that there are so many theories on specific things that drove our evolution from an ancestor who was ostensibly more like a modern chimp than a modern human, most of them having some merit, that it was likely a combination of things more than any single specific overwhelming benefit.

Given that it now seems clear chimps can and do use tools in the wild, I sometimes wonder if freeing up the hands for use of tools/weaponry was a major driving factor or more of a nice side-effect.

Ross

[Gerrard Farrell]

Re: The evolution of bipedalism

People look at the modern chimp ,pick out tasks that the chimp performs in an upright , bipedal stance ,and then suggest that this behaviour or group of behaviours ,combined in the last common ancestor ,led to bipedalism . The problem with this type of argument is that modern chimps can easily perform bipedal tasks whilst retaining the advantages of their present phenotype and this was also probably true of the last common ancestor . Evolving into an obligate biped limits options and would only be selected for if it also produced abilities that are not available to chimps . In the first instance ,before an effective running phenotype evolved ,this would have been ground up ,high speed , high kinetic energy tool use .

[Gerrard Farrell]

Re: The evolution of bipedalism

Edmund, perhaps a good question ,which I have never seen asked ,might be what abilities would an animal with a chimp like phenotype lose ,or have to a lesser degree , if it evolved into an early obligate biped ? .
Also , what would happen if a group of newly evolved bipeds ( newly evolved from a chimp like ancestor ) found its self in direct competition for territory and food with a group of knuckle walking quadruped chimp like animals ?

[Drew Smith]

Re: The evolution of bipedalism

I think it is very important to consider how much climate and climate change influenced so many adaptations: if the climate changed such that forests became savannahs over a relatively short period of time, then spending more time on hindlimbs surveying above the grasses may have helped to give early warning to approaching dangers, for instance. Being able to take advantage of upper limbs being free to manipulate tools may have just been an added bonus but not the driving force behind bipedalism.

[Gerrard Farrell]

Re: The evolution of bipedalism

Hi Drew
Standing tall ,cautiously , every now and again to see what's about may be a good idea but being permanently upright has been proposed as an a disadvantage in high grasses . This is because if you are head and shoulders above the level of the grass your location would become obvious to predators from long distances .These would then stalk you by remaining low ,in a crouch , below the grasses , as lions etc do .


With regard to the enormous advantages that tool use can provide you might be interested in the extract (below) which I wrote some time ago -( I take the earlier point about modern chimp tool use but to actively hunt in the way described below an ape would have to stand tall and carry a stick along with it . No point in finding prey and then looking for a stick . )

EXTRACT
So is there any consensus between the scientists in the various fields of science involved in studying evolution on the driving forces behind the development of bipedalism in hominids that eventually led to homo sapiens ?

Well my take on it , for what that is worth , is as follows -

The introduction of “biological clock” studies has now puts the split between the lines leading to chimpanzees (pan ) and us (homo) as happening between 10-7 million years ago . It has to be said that some confusion exists over the speed at which this clock ticks ,but lets go with that figure .
So how did our ancestors split away from the lineage of the genus pan and how did bipealism develop ?

Some authorities think that bipedalism developed among a subgroup of great apes involved in brachiation in forest trees with our early ancestors having a gibbon like phenotype ( note they do not say we descended from gibbons but that later more advanced apes became gibbon like through convergent evolution ).

A large amount of work has been carried out on the anatomy of gibbons and the biomechanics of gibbon movement and it does seem plausible that our ancestors developed similar bodies which encouraged bipedal locomotion .
But if such a creature leaves the trees and becomes more terrestrial what evolutionary factors continue to select for bipedalism .
Many ideas have been forwarded for bipedalism and some are listed here -

1 Bipedalism frees up the hands for tool use (Darwin )

2 Hands freed up for males to take collected food back to a chosen location to feed a female and their offspring

3 Seeing over tall grass the better to see predators

4 More energy efficient locomotion

5 Radiation avoidance - a upright stance might reduce heating of the brain

Etc

When considering the first of these proposals ,that bipedalism frees up the hands for tool and weapon use there seems to be a tendency among those discussing the subject to point out that the use of stone tools started only about 2.5 million years ago and that only stick use by early upright hominids might be a possibility . Thereafter in such discussions tool use ( sticks) seems to be rejected in favour of some of the other alternative suggestions for bipedalism .

However I would argue that a gibbon like ape armed with a sick is a totally different proposition than a a gibbon like creature without a stick .

With its bipedal agility and large opposable thumb , a slightly more neurologically advanced gibbon like ape would be able to take a longish stick of suitable weight and , by incapacitating previously unapproachable prey species with the stick, begin to occupy an ecological niche not open to the other great apes .

Such new prey species might include large arachnids ,reptiles and even small mammals .

For example animals such as large spiders and scorpions ,which adopt a static , threatening posture when they themselves feel threatened ,would cease to be food items too hard to tackle and instead become easy to kill with a couple of whacks with a stick .

Its also worth noting that in some parts of India urban rats are still hunted with a simple stick showing how effective this method can be .

Even poisonous snakes ,normally a complete no go for a 10kg ape might be on the menu .

So in summary then early hominids might have evolved a gibbon like phenotype through brachiation and then progressively moved to the ground there hunting with a stick gave them a great advantage over other animals and which allowed bipdalism to continue to be selected for .

[Gerrard Farrell]

Re: The evolution of bipedalism

For those interested here are another couple of posts from the same thread as the one above . They explore the way in which the unshod forefoot functions to provide grip and the causes of the pathological changes seen in the foot when the intrinsic muscles become atrophied . I have included a link to the full thread at the end of this post .


EXTRACT 1
Following on from the posts above perhaps the chimpanzee -human last common ancestor gave rise to a gibbon like phenotype which eventually became terrestrial once more leading to the extant Homo (human) genera of homini . Us

If this happened then the foot of our brachiating ancestors would need to evolve from a grasping structure to something that functions in a quite different way since in my opinion human toes cannot be said to grasp the ground but act to allow traction by remaining straight other than flexing around the metatasophalangeal joints.

Provided at the end of this post is a link to a fossil footprint made about 1.5 million years ago ,possibly by Homo Erectus . You can see that there is a mound of material left between imprints of the toes and the ball of the foot . To me this clearly indicates that even on slippery surfaces the toes of this almost human foot , do not curl but stay straight to maintain traction . The toes do not grasp the ground they remain as straight as possible and presumably hinge around the metatarsophalangeal joints . If the toes curled then the material between the toes and ball of the foot would be extruded giving less grip not more .

Any thoughts

Gerry

https://www.theguardian.com/world/2009/feb/27/earliest-human-footprint-found

Earliest human footprints found in Kenya | World news ...
www.theguardian.com
Footprints found on a sandy plain in eastern Africa have been hailed by scientists as the earliest evidence of modern upright walking. The footprints, dated to ...


EXTRACT 2

Surely with regard to traction the interaction between the substrate and the standing foot is about more than just friction .After all, on a yielding soil imprints are created and within these imprints we find ridges and depressions .
To me this indicates a gravity driven ,passive grip system in the forefoot and also helps to explain the vital role of toe nails in substrate /foot interaction .

The grip system I have in mind will only work optimally if the toes remain straight as the heel of the standing foot lifts from the ground leaving only the ball of the foot and the toes in contact with the ground .

So why do some toes curl during locomotion ?

In brief, in my opinion, the toes will adopt the position of maximum mechanical advantage, for given strength levels in the musculature, when called upon to bare load /produce force during standing or locomotion .

In groups with well developed foot musculature I would predict that the toes will generally remain straight when called upon to perform work. However ,when a foot with weak musculature is called upon to perform work the toes will collapse into hammer or claw toe type positions since it is only these shortened positions that weak toes can perform their roles during gait .

In summary, weakened toes will collapse into the position of maximum mechanical advantage for given strength levels when challenged with load .

In fact I believe this may true of the entire foot with people suffering from pathologically driven atrophy of the intrinsic musculature developing shortened feet with high arches and proximally/dorsally migrated metatarsal /phalangeal joints .

It may be worth noting that this collapsing/shortening of foot structure will ,in my opinion , be most obvious in feet which become weakened but which continue to be subjected to normal loads . If and individual with severely weakened feet subconsciously reduces the load to which the foot is subjected by a change in gait strategy ,for example the adoption of a high stepping gait that avoids toe off ,then perhaps changes in toe/foot morphology are avoided .



LINK TO FULL THREAD

Born not to run but to reproduce | Podiatry Arena

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25 Jun 2016 - So why are we the shape we are . Why are feet the shape they are and why is the human scapula configure as it is . Yes they respectively allow us to run and throw but I believe these may notbe the primary driving evolutionary forces . Monolith apart I think Kubrick sums things up nicely in this clip . 2001: A ...

[Edmund Cramp]

Re: The evolution of bipedalism

With respect, I wonder if bipedalism might not simply be one of those things that “evolved” as a byproduct of other evolutionary pressures?

I was watching the BBC documentary Galapagos the other day and listening to Tilda Swinton describing the “evolution” of different shaped tortoise shells on different islands as “offering an evolutionary advantage” but I just can’t see how that should be the case - clearly, in the Galapagos, size is a significant factor in the ability of the tortoise to survive the variable climate, but the shape of the shell? They are all similar - so assigning this to evolution seems to a bridge too far.

Could bipedalism be the same thing? We’re all involved in biomechanics so we like to think of our human biomechanics as offering some significant advantage but, if it is as good as we think it is, why hasn’t it evolved elsewhere? Other than our chimp family tree, the only other vaguely bipedal animal in the past that I can think of were the Dinosaurs - and faced with an environmental disaster they seem to have found feathered flight far more useful from an evolutionary standpoint. In today's world it's just the Kangaroo, but I can't really see the Kangaroo family as being bipedal in the same way that the first chimps descending from the trees were bipedal. All too often I think we ignore happenstance in Science.

On a lighthearted note, it’s December and so, in the US at least, the Frank Capra film “It’s a Wonderful Life” is being shown on TV again. This always makes me think of Stephen Jay Gould’s book on the Burgess Shale and evolutionary history which has been a big influence on my view of evolution.

[Gerrard Farrell]

Re: The evolution of bipedalism

Hi Edmund
A recent press release from South Africa has revealed the fossilized remains of a hominid which dates from about 3.6 million years ago (see link below ) . Called "Little Foot " , the skeleton is almost complete and would have belonged to an animal which still had a foot suitable for living in the trees but walked on the ground as a biped .

So it might be fair to say that the arrangement of the pelvis , foramen magnum and femur needed for bipedalism evolved through brachiation and that the skeletal arrangement arrived at could be used for developing ground up, rotational , high energy kinetic energy in hand held objects .

This leg driven use of tools might have given sufficient advantage to be selected for , resulting in the evolution of a more terrestrial group of hominids with a non divergent first ray in the foot which would be better suited to bipedalism .

So brachiation leads to upright posture giving high energy tool use then commitment to bipedalism ., Simple !


link -Little Foot skeleton unveiled in South Africa - BBC News

www.bbc.co.uk/news/world-africa-42250530


6 Dec 2017 - One of the oldest and most complete skeletons of humankind's ancestors has been unveiled in South Africa. A team spent more than 20 years excavating, cleaning and putting together the skeleton of Little Foot. Its exact age is debated, but South African scientists say the remains are 3.67 million years old.

[Gerrard Farrell]

Re: The evolution of bipedalism

So why would a non divergent first ray and the development of a medial longitudinal arch be of benefit to an obligate biped ?

Perhaps one reason might be because pronation of the foot would allow a more liner progression of the COM during gait with less lateral movement since a pronating foot allows the weight bearing tibial head to move towards the medial sagittal plane .

Any thoughts ?