Animals have a problem.\u00a0 They need to eat.\u00a0 To do that, at some point in their lives, they\u2019ve got to move about and find food.\u00a0 Plants never have to worry about this, they can make all the chemicals they need to live and grow by the process of photosynthesis.\u00a0 By capturing the energy of sunlight, they are able to turn the simple chemicals around them: Carbon Dioxide, Oxygen and mineral compounds, into the complex organic chemicals: Carbohydrates, Proteins and Fats that they need. \u00a0If animals could photosynthesise it would be a very different world indeed, however, they can\u2019t because they\u2019re too dense and opaque.\u00a0 The only way animals can get those essential energy-giving and bodybuilding chemicals is to eat either plants, or other animals.<\/p>\n
There are of course some animals that move very little throughout their lives: corals, sponges, barnacles and sea anemones, to name but a few.\u00a0 But even the world\u2019s most sedentary animals often have a surprising double life, with a larval stage that travels far and wide before it attempts to settle in a suitable location.<\/p>\n
The need to travel about in order to: find food, escape predation by bigger animals, find shelter and find a mate, is central to the lives of all animals.\u00a0 So where do you start if you\u2019re going to look at animal locomotion?\u00a0 Well, how about walking?\u00a0 We do it all the time and we do it for most of our lives.\u00a0 It can\u2019t be that complex?\u00a0 Can it?<\/p>\n
There are many land animals that don\u2019t bother with walking (or legs) at all.\u00a0 Nematode worms manage to burrow through the soil in much the same way as an eel swims through water.\u00a0 Molluscs (slugs and snails) are swimmers too, travelling with the aid of ordered ripples of muscle contraction and a specially created sheet of watery slime.\u00a0 The Annelids (earthworms) have a clever way of pulling themselves along by alternately anchoring and stretching their body segments.\u00a0 You will find countless thousands of these animals living in the soil of every continent on Earth except Antarctica.\u00a0 They are essential to the proper functioning of every ecosystem on the planet.\u00a0 However, it\u2019s the animals with legs that have really colonised the surface of the Earth and dominate to this day.<\/p>\n
Although legs and feet aren\u2019t as efficient as wheels and an engine, they can cope with hills, rough tracks, ditches, stairs and all manner of obstacles that wheeled vehicles would find impassable.\u00a0 But even animals that live in flat places don\u2019t have wheels.\u00a0 This is because there is no such thing in nature as an axle with a bearing which can rotate freely around it, an essential component of wheeled vehicles.\u00a0 An animal\u2019s limb can only go so far in any direction before it has to be \u201creset\u201d by returning it to its starting position.\u00a0 It\u2019s attached to the rest of the animal by tendons, muscles, blood vessels and nerves that would all tear and snap if the limb rotated freely.\u00a0 Humans and the other apes come close with their special \u201cball and socket\u201d shoulder joint that allows us to reach all round with our arms and swing under branches (we still can\u2019t spin them round in a true circle however).<\/p>\n
The first many-legged beasties to walk on earth were exactly that; many legged.\u00a0 They were the arthropods: millipedes, centipedes, scorpions, spiders, woodlice, springtails, and insects (in roughly that order).\u00a0 Their strong, chitin based exoskeletons protected them from damage by both the sun\u2019s rays, and the harsh terrestrial environment.\u00a0 But as well as protection, their body armour, made of segments that could move freely, gave them another great advantage: jointed legs.\u00a0 These were animals really built for colonising the surface of the planet, and they did just that from around 420 million years ago.\u00a0 Today, they are still the most successful group of animals on Earth.\u00a0 80% of all the animals known to science are arthropods and you find them everywhere, including Antarctica.\u00a0 The arthropods don\u2019t win all the design awards however, as their exoskeletons cause them a few tricky problems.\u00a0 Firstly, they can\u2019t grow without shedding their skins, a dangerous thing to do as it leaves them temporarily soft-bodied, unable to move and at risk from predation, water loss and physical damage, whilst they wait for the new bigger skin underneath to dry.\u00a0 Secondly, the skeletons, though strong for their weight, need to become so bulky and heavy to support the weight of a large animal that they become impractical.\u00a0 This is one of the factors that creates an upper limit on the size of terrestrial arthropods (the other is breathing).<\/p>\n
The next big step in leg design happened around 340 million years ago when some particularly muscle-bound fish started to take advantage of tasty terrestrial titbits of food.\u00a0 Their strong \u201cwalking fins\u201d formed the blueprint for the pentadactyl limb design that all tetrapod vertebrates (animals with four legs and backbones) share.\u00a0 Their descendants were the amphibians, reptiles and eventually the mammals.\u00a0 Unlike the arthropods, the internal skeletons of vertebrates are made of living tissue and grow as the animal does.\u00a0 Although bony skeletons are much heavier than the skeletons of arthropods, vertebrate skeletons are incredibly strong and some terrestrial vertebrates, notably the Dinosaurs grew incredibly large.<\/p>\n
Despite the differences between the skeletons of arthropods and vertebrates, when it comes to walking, both skeletons do the same job in much the same way.\u00a0 They are strong, rigid, and act as levers to which the animal\u2019s muscles are attached.\u00a0 When the muscles contract, they exert a force against the skeleton, which is transferred to the ground in order to propel the animal along.<\/p>\n
This is something robot engineers and biologists alike are keen to sort out, as it has wide implications.\u00a0 Does an animal (or robot) use less energy swinging a large number of small legs than it would were it to swing fewer, larger legs?\u00a0 Recent research by biomechanics specialists at the University of California has produced some surprising results.\u00a0 They claim that it actually makes little difference to the overall efficiency of the animal.\u00a0 According to them, animals bounce as they move using two alternating sets of legs as springs.\u00a0 This means that one human leg ends up being equivalent to two dog legs, three cockroach legs or four spider legs, five crab legs, etc. in terms of energy output per kilogram of body mass.<\/p>\n
The claims are startling, as traditionally the splayed leg arrangement that you see in many animals, both arthropods (scorpions and spiders) and tetrapod vertebrates (newts and toads), was always considered to be inefficient.\u00a0 This was because this particular limb arrangement causes the animal to rock at each step so that any energy spent moving forward is also \u201cwasted\u201d moving from side to side.\u00a0 Animals like dinosaurs and mammals, which have shoulders, positioned close together, narrow pelvises and limbs which extend down, almost vertically, from the body were thought to be more efficient because all their energy was directed into forward movement.\u00a0 Also, the position of their legs allowed them to take longer strides than would otherwise be possible.\u00a0 This research actually suggests that the rocking action, far from being a hindrance, is a good thing as it causes the animal to behave like a pendulum, aiding movement and making it more, not less efficient.<\/p>\n
The scientists\u2019 work continues, and soon we should have a better idea as to the real reason for the long straight strides that mammals take as they walk.\u00a0 Until then, I\u2019m inclined to stick to the old theory that it\u2019s a more efficient way of getting from A to B than waddling!<\/p>\n
There are, of course, many reasons why having lots of legs can be useful.\u00a0 An animal needs a lot less brainpower to control and balance on four, six or eight legs, as it\u2019s an arrangement that provides the animal with a wide base of support and a low centre of gravity.\u00a0 It\u2019s no accident that all the successful robots and automatic walking machines humans have created have six or eight legs, to allow them to move about with the minimum of computer power.<\/p>\n
Because humans are bipedal (we walk our hind two limbs), we tend to think of that as the normal way to be.\u00a0 In actual fact, it\u2019s unique.\u00a0 No other animal can do it for any length of time.<\/p>\n
Walking and balancing on two legs is a lot harder than it looks, it requires a huge amount of brainpower.\u00a0 Even when you\u2019re standing still, your brain has to constantly monitor the signals coming in from: your eyes, the pressure sensors on the soles of your feet, the tension sensors in your muscles and the balance sensors in your inner ear.\u00a0 Based on all that information, your brain then sends out a constant stream of instructions to your muscles to tense or relax as necessary, to ensure that your centre of gravity stays \u201ccentral\u201d and doesn\u2019t pull you over.\u00a0 If you want to see how this combination of senses and fast reactions works, try this test:\u00a0 Stand up, hold your arms straight out in front of you, keep your arms out, stand on tiptoe, hold it for twenty seconds.\u00a0 That shouldn\u2019t have given you any trouble, but now I want you to do it again \u2013 and when you\u2019re on tiptoe, close your eyes!\u00a0 It\u2019s much harder to balance without your eyes providing that extra information.\u00a0 Animals with four or more legs don\u2019t have to try so hard as they are much more stable.<\/p>\n
Being bipedal creates some other interesting problems for humans.\u00a0 Because we need a big brain we naturally have babies with big brains.\u00a0 However, babies with big brains have to have big heads.\u00a0 Big headed babies need mothers with a wide pelvis and large birth canal through which they can fit, and be born.\u00a0 All fine so far, except that in order to walk efficiently, us mammals need to have a narrow pelvis.\u00a0 Humans have evolved a remarkable solution to the problem, they give birth prematurely!\u00a0 At the point when they\u2019re born, human babies are completely unable to do that most basic of human activities, walking.\u00a0 After nine months in their mother\u2019s womb, long enough for their bodies to fully form, babies\u2019 brains are far from fully grown.\u00a0 In fact, human babies; brains grow at the pre-birth (foetal) rate for a whole year after birth.\u00a0 No other animal does this.<\/p>\n ","protected":false},"excerpt":{"rendered":"
Why move at all? Animals have a problem.\u00a0 They need to eat.\u00a0 To do that, at some point in their lives, they\u2019ve got to move about and find food.\u00a0 Plants never have to worry about this, they can make all the chemicals they need to live and grow by the process of photosynthesis.\u00a0 By capturing […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"spay_email":"","jetpack_publicize_message":"","jetpack_is_tweetstorm":false},"categories":[3,4],"tags":[8,23,7],"jetpack_featured_media_url":"","jetpack_publicize_connections":[],"jetpack_shortlink":"https:\/\/wp.me\/s2VEjn-walking","jetpack_sharing_enabled":true,"_links":{"self":[{"href":"https:\/\/www.howiewatkins.co.uk\/index.php?rest_route=\/wp\/v2\/posts\/16"}],"collection":[{"href":"https:\/\/www.howiewatkins.co.uk\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.howiewatkins.co.uk\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.howiewatkins.co.uk\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.howiewatkins.co.uk\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=16"}],"version-history":[{"count":1,"href":"https:\/\/www.howiewatkins.co.uk\/index.php?rest_route=\/wp\/v2\/posts\/16\/revisions"}],"predecessor-version":[{"id":17,"href":"https:\/\/www.howiewatkins.co.uk\/index.php?rest_route=\/wp\/v2\/posts\/16\/revisions\/17"}],"wp:attachment":[{"href":"https:\/\/www.howiewatkins.co.uk\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=16"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.howiewatkins.co.uk\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=16"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.howiewatkins.co.uk\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=16"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}