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Thread: The evolution of bipedalism

  1. #11

    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 . )

    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


    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 .

    Last edited by Gerrard Farrell; 11-30-2017 at 11:09 AM.

  2. #12

    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 .

    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


    Earliest human footprints found in Kenya | World news ...
    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 ...


    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 .


    Born not to run but to reproduce | Podiatry Arena › Forums › General › General Issues and Discussion Forum

    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 ...

  3. #13
    Join Date
    Jan 2011
    Baton Rouge, Louisiana USA

    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.
    Last edited by ecramp48; 01-05-2018 at 10:34 AM. Reason: changed the font, nothing else

  4. #14

    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

    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.

  5. #15

    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 ?

  6. #16
    Join Date
    Jan 2011
    Kingston, ON

    Re: The evolution of bipedalism

    I really enjoyed reading this thread! Lots to think about now. FYI. There is a great chapter (15) by John Fleagle and Dan Lieberman in the book 'Great Transformations in Vertebrate Evolution' edited by Dial, Shubin, and Brainerd (2015) that nicely summarizes some of these topics. Eddie, Wonderful Life by Gould also had a tremendous impact on me. There is a new book out by Jonathan Losos called 'Improbable Destinies' (2017) that uses recent work to reconcile Gould and others' ideas on contingency with Simon Conway-Morris' and others' ideas on evolutionary convergence. Really good book!

  7. #17
    Join Date
    Jan 2011
    Baton Rouge, Louisiana USA

    Re: The evolution of bipedalism

    Thank you for the suggestion, I'll add that to my reading list. I do find these discussions very educational, they promote a host of new ideas and thoughts - if only I had more time to follow them all up. As a child back in the 1950's I was fascinated by the discussions that seemed to imply that our earliest ancestors might go back half a million years, and now this time frame keeps being pushed further and further back. Every time we learn a little more about human evolution, we discover that there is so much more than we suspected in our past. It really is A Wonderful Life!

  8. #18

    Re: The evolution of bipedalism

    Recently ,in the process of comparing the Chimpanzee rearfoot to that of a human it occurred to me that of one of the ways in which the intrinsic foot muscles contribute to balance might be as follows
    The question I asked myself was what type of balance system can take the apparently difficult to balance , tall ,top heavy ,human phenotype and use this shape to advantage ?

    Well , first consider balancing a pencil on your finger . Its very difficult .
    Easier to balance is a long broom handle due to inertia . Easier still is the act of balancing a complete broom on your finger /palm with the broom head in the air and the end of the broom on your hand .
    So can the head of the tibia balance in this way on the talus/calcaneal unit ? I think the answer may be yes , at least for postural stability in the medio lateral direction .

    Previously , Luke Kelly (1) has shown that the intrinsic foot muscles can control foot posture including the condition of the medial longitudinal arch and ,in my opinion ,this could lead to inversion and eversion of the calcaneus, and then via the talus ,to a movement of the tibal head relative to the COG .

    Another paper has shown that the vestibular apparatus has a direct link to some of the intrinsic foot muscles showing the have a key role in balance . (2)

    A third paper (3) indicates that in the absence of strong intrinsics the extrinsics seem take on more of role in postural stability an so enlarge .

    So what I am saying overall is that the intrinsics handle small medio lateral perturbations via calcaneal positioning and with larger perturbations the extrinsics kick in to assist .

    This theory places the intrinsics right at the very heart of human balance .

    Any thoughts

    Paper 1 Recruitment of the plantar intrinsic foot muscles with increasing ... Dec 2017 - Full-text (PDF) | The aim of this study was to determine the difference in activation patterns of the plantar intrinsic foot muscles during two quiet standing tasks with increasing postural difficulty. We hypothesised that activation of these muscles would increase with increasing postural demand...

    Paper 2
    vestibular modulation of the abductor hallucis and the ... - Scholars' Bank Thesis-Wallace.pdf?...1
    by J Wallace - ‎2016 - ‎Related articles
    explore the vestibular system. The purpose of this experiment was to determine if intrinsic foot muscles are modulated by vestibular activity and to elucidate any changes in the association between the vestibular stimulation and electromyography (EMG) responses in response to changes in head position, visual cues, and ...

    Paper 3
    Foot muscle morphology is related to center of pressure sway and ...
    by X Zhang - ‎2017 - ‎Related articles
    Gait Posture. 2017 Sep;57:52-56. doi: 10.1016/j.gaitpost.2017.05.027. Epub 2017 May 25. Foot muscle morphology is related to center of pressure sway and control mechanisms during single-leg standing. Zhang X(1), Schütte KH(2), Vanwanseele B(3). Author information: (1)Human Movement Biomechanics Research ...

    Gerrard Farrell


  9. #19

    Re: The evolution of bipedalism

    Here are some further posts made originally be me ,today, on "Podiatry Arena "


    • With regard to the above it would appear that babies can hold their bodies in an upright position long before they can balance on their feet . Included below is a link to a video of a man balancing babies on the palm of his hand with the babies holding themselves straight whilst the man moves his hand to keep them balanced . A bit like the head of the tibia balancing on the taloncalcaneal complex with the intrinsics keeping things in balance .

      Note -in the video the authors point out that the activities shown in the video should not be tried at home !

      Icelandic swim instructor teaches babies to stand on their own ...

      ▶ 1:45

      20 Jul 2017 - Uploaded by Business Insider UK
      Snorri Magnusson is Iceland's "Baby Whisperer." The swimming instructor teaches babies as young ...
      Gerrard Farrell


      scotfoot, Today at 11:11 AM

    • scotfootActive Member

      Look at figure 6 in the paper below . Again, Luke Kelly .

      Intrinsic foot muscles have the capacity to control deformation of the ...
      by LA Kelly - ‎2014 - ‎Cited by 50 - ‎Related articles
      29 Jan 2014 - We test the hypotheses that activation of the three largest plantar intrinsic foot muscles, abductor hallucis, flexor digitorum and quadratus plantae is associated with muscle stretch in response to external load on the foot and that activation of these muscles (via electrical stimulation) will generate sufficient ...
      Gerrard Farrell


      scotfoot, Today at 11:55 AM

    • scotfootActive Member

      Further to the above , an extremely interesting paper was very recently published , Koyama et al 2017 (below) , which looked at fatiguing the muscles of the foot and the effect this has on postural sway . They found that the exercises reduced some aspects of postural sway .
      The authors stated -

      "This study revealed that fatiguing foot muscle exercises decreased foot muscle strength and altered postural sway during standing. Interestingly, the fatiguing foot muscle exercises decreased the COP range and velocity while standing compared with the pre-fatigue conditions. The decreased foot muscle strength after the exercises was not associated with changed postural sway during standing after the exercises ".

      What makes this paper so interesting is that the exercises used in the study would have fatigued the extrinsic foot muscles but not the intrinsics ( calf raises and toe curls do not target the intrinsics and a toe grip dynamometer measures extrinsic toe flexor strength )

      Contrary to the interpretation of the authors I believe this paper may show better postural stability with less extrinsic foot muscle input and greater reliance on the intrinsics .

      Altered postural sway following fatiguing foot muscle exercises - PLOS
      by K Koyama - ‎2017
      7 Dec 2017 - The activities of the intrinsic and extrinsic plantar muscles contribute to postural stability during upright standing, especially in the single-leg standing [9]. Foot muscle strength is considered to be one of the important essentials that provides postural control while standing [10]; however, the relationship between foot muscle ...
      Gerrard Farrell


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