What features of the human body are due to upright posture. Upright posture arose as a result of a rare mutation
bipedalism
Cycle of walking: support on one leg - double support period - support on the other leg ...
Walking man- the most natural human locomotion.
There are other definitions that characterize this locomotion:
"... synergies covering the entire musculature and the entire motor apparatus from top to bottom"
"... a cyclic act, that is, a movement in which the same phases are periodically repeated again and again."
- Walking is a motor action, the result of the implementation of a motor stereotype, a complex of unconditioned and conditioned reflexes.
- Walking is a motor skill, which is a chain of sequentially fixed conditioned reflex motor actions that are performed automatically without the participation of consciousness.
Words that are close in meaning:
- en:gait - walking.
- "gait" en: walking - features of postures and movements when walking, characteristic of a particular person.
- "Posture" en: Posture - the usual position of the human body at rest and movement, including when walking.
Types of walking
| as natural locomotion: | as sports and health locomotion: | as a military-applied locomotion |
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Marching (eng.) (organized walking, an exercise in measured walking in regular rows) |
Types of walking should not be confused with types of gait. Walking is a motor act, a kind of motor activity. Gait - a feature of a person's walking, "manner of walking"
Walking tasks
Tasks of walking as an important locomotor function:
- Safe linear translational movement of the body forward (the main task).
- Maintain vertical balance, prevent falling when moving.
- Conservation of energy, the use of a minimum amount of energy due to its redistribution during the step cycle.
- Ensuring smooth movement (sudden movements can cause damage).
- Gait adaptation to eliminate painful movement and effort.
- Preservation of gait under external disturbing influences or when changing the plan of movements (Stability of walking).
- Resistance to possible innervation and biomechanical disorders.
- Optimization of movement, first of all, increasing the efficiency of safely moving the center of gravity of the masses with the least energy consumption.
Walking Options
General walking parameters
The most common parameters characterizing walking are the line of movement of the center of mass of the body, stride length, double step length, foot turn angle, support base, movement speed and rhythm.
- The base of the support is the distance between two parallel lines drawn through the centers of the support of the heels parallel to the line of movement.
- Short stride is the distance between the heel pivot point of one foot and the heel pivot point of the contralateral leg.
- The turn of the foot is the angle formed by the line of movement and the line passing through the middle of the foot: through the center of the heel support and the point between the 1st and 2nd fingers.
- The rhythm of walking is the ratio of the duration of the transfer phase of one leg to the duration of the transfer phase of the other leg.
- Walking speed - the number of large steps per unit of time. Measured in units: step per minute or km. in hour. For an adult - 113 steps per minute.
Biomechanics of walking
Walking for various diseases is studied by the section of medicine - clinical biomechanics; walking as a means of achieving a sports result or increasing the level of physical fitness is studied by the section of physical culture - sports biomechanics. Walking is studied by many other sciences: computer biomechanics, theater and ballet art, military science. The basis for the study of all biomechanical sciences is the biomechanics of a healthy person walking in natural conditions. Walking is considered from the standpoint of the unity of biomechanical and neurophysiological processes that determine the functioning of the human locomotor system.
Biomechanical structure of walking = + + +
The temporal structure of walking is usually based on the analysis of the results of the podography. Podography allows you to register the moments of contact of various parts of the foot with the support. On this basis, the time phases of the step are determined.
The kinematics of walking is studied using contact and non-contact sensors for measuring angles in the joints (goniometry), as well as using gyroscopes - devices that allow you to determine the angle of inclination of a body segment relative to the line of gravity. An important method in the study of the kinematics of walking is the cyclography technique - a method for registering the coordinates of luminous points located on body segments.
The dynamic characteristics of walking are studied using a dynamographic (power) platform. When supporting the power platform, the vertical reaction of the support is recorded, as well as its horizontal components. To register the pressure of individual sections of the foot, pressure sensors or strain gauges are used, mounted in the sole of the shoe.
The physiological parameters of walking are recorded using the electromyography technique - registration of muscle biopotentials. Electromyography, compared with the data of methods for assessing the temporal characteristics, kinematics and dynamics of walking, is the basis for the biomechanical and inervation analysis of walking.
Temporal structure of walking
A simple two-terminal subgram
The main method for studying the temporal structure is the podography method. For example, the study of walking using the simplest, two-contact electropodography consists in using contacts in the sole of special shoes, which close when supported on a biomechanical track. The figure shows walking in special shoes with two contacts in the heel and forefoot. The period of contact closure is recorded and analyzed by the device: closure of the rear contact - support on the heel, closure of the rear and front contacts - support on the entire foot, closing of the front contact - support on the forefoot. On this basis, build a graph of the duration of each contact for each leg.
Step time structure
The main research methods: cyclography, goniometry and assessment of the movement of a body segment using a gyroscope.
The cyclography method allows you to register changes in the coordinates of the luminous points of the body in the coordinate system.
Goniometry is a change in the angle of the joint by a direct method using angular sensors and non-contact according to the analysis of the cyclogram.
In addition, special sensors are used gyroscopes and accelerometers. The gyroscope allows you to register the angle of rotation of the body segment to which it is attached, around one of the axes of rotation, conventionally called the reference axis. Typically, gyroscopes are used to assess the movement of the pelvic and shoulder girdle, while sequentially registering the direction of movement in three anatomical planes - frontal, sagittal and horizontal.
Evaluation of the results allows you to determine at any moment of the step the angle of rotation of the pelvis and shoulder girdle to the side, forward or backward, as well as rotation around the longitudinal axis. In special studies, accelerometers are used to measure, in this case, the tangential acceleration of the lower leg.
To study walking, a special biomechanical track covered with an electrically conductive layer is used. Important information is obtained when conducting a cyclographic study, traditional in biomechanics, which, as is known, is based on recording the coordinates of luminous markers located on the subject's body by video-film photography.
Walking dynamics
The dynamics of walking cannot be studied by direct measurement of the force that is produced by the working muscles. To date, there are no widely used methods for measuring the moment of force of a living muscle, tendon or joint. Although it should be noted that the direct method, the method of implanting force and pressure sensors directly into a muscle or tendon is used in special laboratories. A direct method for studying torque is also carried out using sensors in lower limb prostheses and joint endoprostheses. An idea of the forces acting on a person when walking can be obtained either in determining the effort in the center of mass of the whole body, or by registering support reactions. In practice, the forces of muscle traction during cyclic movement can only be estimated by solving the problem of inverse dynamics. That is, knowing the speed and acceleration of a moving segment, as well as its mass and center of mass, we can determine the force that causes this movement, following Newton's second law (force is directly proportional to body mass and acceleration).
The real walking forces that can be measured are the ground reaction forces. Comparison of the reaction force of the support and the kinematics of the step makes it possible to estimate the value of the joint torque. Calculation of the muscle torque can be made on the basis of a comparison of the kinematic parameters, the point of application of the support reaction and the bioelectrical activity of the muscle.
Support reaction force
The reaction force of the support is the force acting on the body from the side of the support. This force is equal and opposite to the force exerted by the body on the support.
Vertical component of the support reaction force
Vertical component of the support reaction vector.
The graph of the vertical component of the support reaction during normal walking has the form of a smooth symmetrical double-humped curve. The first maximum of the curve corresponds to the time interval when, as a result of the transfer of body weight to the skating leg, a forward push occurs, the second maximum (rear push) reflects the active repulsion of the leg from the supporting surface and causes the body to move up, forward and towards the skating limb. Both maximums are located above the level of body weight and, respectively, at a slow pace, approximately 100% of body weight, at an arbitrary pace 120%, at a fast pace - 150% and 140%. The support reaction minimum is located symmetrically between them below the body weight line. The occurrence of a minimum is due to the rear push of the other leg and its subsequent transfer; in this case, an upward force appears, which is subtracted from the weight of the body. The minimum support reaction at different rates is the body weight, respectively: at a slow pace - about 100%, at an arbitrary pace - 70%, at a fast pace - 40%. Thus, the general trend with an increase in the pace of walking is an increase in the values of the front and rear shocks and a decrease in the minimum of the vertical component of the support reaction.
Longitudinal component of the support reaction force
Longitudinal component of the support reaction vector it is, in fact, a shear force equal to the force of friction, which keeps the foot from sliding anteroposteriorly. The figure shows a graph of the longitudinal support reaction as a function of the duration of the step cycle at a fast walking pace (orange curve), at an average pace (magenta) and a slow pace (blue).
Point of application of the support reaction force
Ground reaction - these forces are applied to the foot. Coming into contact with the surface of the support, the foot experiences pressure from the side of the support, equal and opposite to that which the foot exerts on the support. This is the reaction of the support of the foot. These forces are unevenly distributed over the contact surface. Like all forces of this kind, they can be represented as a resulting vector, which has a magnitude and an application point.
The point of application of the reaction vector of support on the foot is otherwise called the center of pressure. This is important in order to know where is the point of application of the forces acting on the body from the side of the support. When examining on a power platform, this point is called the point of application of the support reaction force.
The trajectory of the application of the support reaction force
Main biomechanical phases
An analysis of the kinematics, support reactions and the work of the muscles of various parts of the body convincingly shows that a regular change of biomechanical events occurs during the walking cycle. “Walking of healthy people, despite a number of individual characteristics, has a typical and stable biomechanical and innervation structure, that is, a certain spatio-temporal characteristic of movements and muscle work” .
A full cycle of walking - a double step period - is composed for each leg from the support phase and the limb transfer phase.
When walking, a person consistently leans on one or the other leg. This leg is called the supporting leg. The contralateral leg is brought forward at this moment (This is the portable leg). The swing phase is called the swing phase. A full cycle of walking - a double step period - is composed for each leg from the support phase and the limb transfer phase. During the support period, the active muscular effort of the limbs creates dynamic shocks that impart to the center of gravity of the body the acceleration necessary for translational movement. When walking at an average pace, the stance phase lasts approximately 60% of the double step cycle, the swing phase approximately 40%.
The beginning of a double step is considered to be the moment of contact of the heel with the support. Normally, the landing of the heel is carried out on its outer section. From now on, this (right) leg is considered to be the supporting one. Otherwise, this phase of walking is called the front push - the result of the interaction of the gravity of a moving person with a support. In this case, a support reaction arises on the support plane, the vertical component of which exceeds the mass of the human body. The hip joint is in the flexion position, the leg is straightened at the knee joint, the foot is in the position of slight dorsiflexion. The next phase of walking is resting on the entire foot. The weight of the body is distributed on the front and back sections of the supporting foot. The other, in this case, the left leg, maintains contact with the support. The hip joint maintains the flexion position, the knee bends, softening the force of inertia of the body, the foot takes a middle position between the back and plantar flexion. Then the lower leg leans forward, the knee is fully extended, the center of mass of the body moves forward. During this period of the step, the movement of the center of mass of the body occurs without the active participation of the muscles, due to the force of inertia. Support for the forefoot. After about 65% of the time of the double step, at the end of the support interval, the body is pushed forward and upward due to active plantar flexion of the foot - a rear push is realized. The center of mass moves forward as a result of active muscle contraction. The next stage - the transfer phase is characterized by the separation of the leg and the displacement of the center of mass under the influence of inertia. In the middle of this phase, all major joints of the leg are in the position of maximum flexion. The cycle of walking ends with the moment of contact of the heel with the support. In the cyclic sequence of walking, moments are distinguished when only one leg is in contact with the support ("one-support period") and both legs, when the limb extended forward has already touched the support, and the one located behind has not yet come off ("double-support phase"). With an increase in the pace of walking, the "two-support periods" are shortened and completely disappear when switching to running. Thus, in terms of kinematic parameters, walking differs from running in the presence of a two-support phase.
Walking efficiency
The main mechanism that determines the effectiveness of walking is the movement of the common center of mass.
movement of the CCM, Transformation of kinetic (T k) and potential (E p) energy
The movement of the common center of mass (MCM) is a typical sinusoidal process with a frequency corresponding to a double step in the mediolateral direction, and with a double frequency in the anterior-posterior and vertical direction. The displacement of the center of mass is determined by the traditional cyclographic method, indicating the general center of mass on the body of the subject with luminous dots.
However, it is possible to do it in a simpler, mathematical way, knowing the vertical component of the support reaction force. From the laws of dynamics, the acceleration of vertical movement is equal to the ratio of the reaction force of the support to the mass of the body, the speed of vertical movement is equal to the ratio of the product of acceleration to the time interval, and the movement itself is the product of speed to time. Knowing these parameters, one can easily calculate the kinetic and potential energy of each step phase. The potential and kinetic energy curves are, as it were, mirror images of each other and have a phase shift of approximately 180°. It is known that the pendulum has a maximum potential energy at the highest point and turns it into kinetic energy, deviating downward. In this case, some of the energy is spent on friction. While walking, already at the very beginning of the support period, as soon as the GCM starts to rise, the kinetic energy of our movement turns into potential energy, and vice versa, it turns into kinetic energy when the GCM goes down. Thus, about 65% of the energy is saved. Muscles must constantly compensate for the loss of energy, which is about thirty-five percent. Muscles turn on to move the center of mass from the lower position to the upper one, replenishing the lost energy.
Walking efficiency is related to minimizing the vertical movement of the common center of mass. However, an increase in the energy of walking is inextricably linked with an increase in the amplitude of vertical movements, that is, with an increase in walking speed and step length, the vertical component of the movement of the center of mass inevitably increases.
During the stance phase of the stride, there is constant compensatory movement that minimizes vertical movement and ensures smooth walking.
For answers to tasks 29-32, use a separate sheet. First write down the number of the task (29, 30, etc.), and then the answer to it. Write your answers clearly and legibly.
TYPES OF DEVICES
Fitness is the relative expediency of the structure and functions of the body, which is the result of natural selection.
body shape animals allows them to move easily in the appropriate environment, makes organisms inconspicuous in the environment, for example, the rag-picker seahorse. Disguise- the similarity of the organism with any object of the environment in color, body shape, for example, a stick insect. Protective coloration hides the organism in the environment, makes it invisible, for example, a grasshopper. Dissecting coloration- the alternation of light and dark stripes on the body creates the illusion of alternating light and shadow, blurs the contours of the animal, for example, a zebra, a tiger. Warning coloration- bright coloring, indicating the presence of poisonous substances or special stinging organs of protection, the danger of the body to a predator, for example, a bumblebee, a wasp. Mimicry- imitation of unprotected organisms by well-protected ones, for example, deaf nettle. Adaptive behavior- habits, instincts aimed at protection from enemies and the actions of environmental factors (threatening posture, warning and scaring the enemy, freezing, caring for offspring, storing food, building a nest, burrows, etc.).
Plants have also developed adaptations for protection, reproduction and distribution: spines; bright color of flowers in insect pollinated plants; different time of maturation of stamens and ovules prevents the spread of seeds. Modifications of various organs in plants are adaptations to the transfer of adverse conditions and vegetative reproduction.
1) What is the nature of adaptations in living organisms? Explain the answer.
2) Some animals have colors that combine bright colors, such as black and red, black and yellow. What is the biological significance of this coloration?
3) How do plants adapt to lack of moisture? Give examples.
Show answer
1) Adaptations are relative and temporary in nature, as they help the organism to survive only in the conditions in which they arose.
2) This coloration is called warning, indicates the presence of poisonous substances in the animal or special stinging organs of protection, the danger of the body to the predator.
3) Store water in leaves or stems (aloe, cactus); long roots (camel thorn); the leaves are covered with a wax coating or pubescent, hard shoots (saxaul, feather grass) or modified into spines (cacti).
Examine the table "Chemical composition of sugary kelp." Answer the questions.
The chemical composition of sugary kelp
1) To make up for the lack of what element is it recommended to use kelp?
2) How many daily dots of this element does 100 g of dry matter of kelp contain?
3) What disease is prevented by eating kelp?
Show answer
The correct answer must contain the following elements:
3) endemic goiter.
Look at the tables and complete tasks 31 and 32.
Energy costs for various types of physical activity
Vasily is the leading player on the water polo team. Using the data in the tables, offer Vasily an optimal calorie menu that allows him to compensate for energy costs after a workout that lasted 1 hour and 35 minutes.
When choosing, keep in mind that Vasily loves chocolate ice cream, and drinks tea without sugar.
In your answer, indicate energy costs, recommended meals, calorie content of lunch and the amount of fat in it.
Show tablesEnergy and nutritional value of products
A person is characterized by the vertical position of the body, based only on the lower limbs. The spine of an adult has curves. During fast, sharp movements, the curves spring back and soften shocks. In mammals, which rely on four limbs, the spine does not have such bends.
The human chest is expanded to the sides due to upright posture. In mammals, it is laterally compressed.
One of the most characteristic features of the human skeleton is the structure of the hand, which has become an organ of labor. The bones of the fingers are mobile. The most mobile, well-developed thumb in humans is located opposite all the others, which is important for various types of work - from chopping firewood, which requires strong sweeping movements, to assembling wristwatches, which is associated with thin and precise finger movements.
The massive bones of the lower extremities of a person are thicker and stronger than the bones of the arms, since the legs bear the entire weight of the body. The arched foot of a person when walking, running, jumping springs, softens shocks.
In the skeleton of the human head, the cerebral part of the skull predominates over the facial part. This is due to the great development of the human brain.
2.4. First aid for skeletal injury
First aid for sprains and dislocations. As a result of awkward movements or bruises, the ligaments that connect the bones in the joint can be damaged. There is swelling around the joint, sometimes hemorrhage, severe pain occurs. This joint injury is called stretching.
When providing assistance to the damaged area, you need to attach an ice pack or a towel moistened with cold water. Cooling relieves pain, prevents the development of edema, and reduces the volume of internal circulation. When the ligaments are sprained, a tight fixing bandage is also needed. It is impossible to stretch, pull and heat the damaged limb. After giving first aid, you need to see a doctor.
Awkward movements in the joint can cause a strong displacement of the bones - dislocation. With a dislocation, the articular head comes out of the articular cavity. There is a sprain, and sometimes a rupture of the ligaments, which is accompanied by severe pain. Trying to repair a dislocation without a doctor can cause even more serious damage.
First aid for a dislocation is to first provide complete rest to the joint. The hand should be hung on a scarf or bandage, and a splint should be placed on the leg using improvised means (planks, strips of thick cardboard). To reduce pain, an ice pack or cold water should be applied to the injured joint. Then the victim must be taken to the doctor.
First aid for broken bones. Despite the strength, with injuries, severe bruises, falls, bones sometimes break. Occur more often fractures limb bones.
If a fracture is suspected, only the complete immobility of the damaged part of the body will relieve pain and prevent the displacement of bone fragments, which can damage the surrounding tissues with sharp edges.
The broken limb is immobilized with a splint bandage. Special tires are available in medical institutions and pharmacies. At the place of origin, they can be made from boards, branches, cardboard. To prevent the tire from pressing on the fracture, a soft bedding is placed under it. The tire should be located not only on the damaged area, but also on neighboring ones. So, in case of a fracture of the bones of the forearm, the splint should go both on the shoulder and on the hand. In this case, parts of the broken bone do not move. The tire is tightly bandaged to the limb with wide bandages, a towel, etc. If there is no splint, the broken arm is bandaged to the body, and the injured leg to the healthy one.
At open fractures the sharp ends of a broken bone rupture muscles, blood vessels, nerves, and skin. Then you need to treat the wound, apply a clean bandage, and then a splint.
Not every fracture can be splinted. If a fracture is suspected ribs the victim is asked to exhale as much air as possible from the lungs and then breathe shallowly. With such breathing, the chest is tightly bandaged. The ribs tightened in the exhalation position make very limited movements.
For fractures spine it is necessary to lay the victim on a flat hard surface face down and call an ambulance. In no case should the victim be transported in a sitting position, since under the weight of the body the spine can move and damage the spinal cord.
For injuries skulls the victim should be laid on his back, his head slightly raised to avoid intracranial hemorrhages and immediately call a doctor.
Russian archaeologist, Ph.D. D., leading researcher of the Department of Paleolithic Archeology of the Institute of the History of Material Culture of the Russian Academy of Sciences (IIMK RAS, St. Petersburg).
"In the beginning there was a leg."
M. Harris. "Our family".
With all the variety of hypotheses that explain the emergence of people, two events are almost invariably put at the forefront, which are considered to be of key importance for the beginning of the process of hominization. These events are the transition of some of the higher apes (hominoids) from a predominantly arboreal lifestyle in forests to a predominantly terrestrial existence in open or mosaic landscapes, and the development of upright walking by them. It is believed that the first, having put the ancestors of hominids in front of the need to adapt to a new, unusual environment, pushed them to search for new ecological niches and stimulated the development of tool activity, sociality, etc., and the second, which resulted in the release of the forelimbs from the musculoskeletal function , was a necessary prerequisite for such development. If it were possible to explain what exactly led to a change in the habitat, which led to a change in the way of movement, and, most importantly, why these two events made adaptation insufficient by the usual biological way, pushing for the realization of cultural (that is, primarily intellectual) potential, then the main problem of anthropogenesis could be considered solved in general terms. Meanwhile, the answer is more or less clear only to the first of the listed questions (more on this later), while regarding the causes and consequences of the transition to upright posture, the range of opinions is very large, and the degree of clarity here is inversely proportional to the growing number of hypotheses. Although very few topics related to the study of anthropogenesis have generated as much discussion as the origin of bipedalism, this event remains a mystery, being truly the "damned question" of paleoanthropology. In theoretical constructions postulating certain sequences of interdependent events in human evolution, this point is the very “weak link”, due to the fragility of which the whole chain crumbles. Since it is impossible to do without this link, its “restoration” is necessary.
Most of the authors who touch upon the origin of bipedalism in hominids are sure that this property from the very beginning gave some advantages to its owners, otherwise it simply would not have arisen. The point of view, no doubt, is absolutely logical, but what, according to those who share it, were these advantages? A lot of answers to this question have been proposed, but none of them, as we will see, can be considered convincing.
According to a widely accepted hypothesis, the transition of human ancestors to upright posture, or, as anthropologists often say, to orthograde locomotion, was explained by the need to adapt to open landscapes, i.e. to life in the savannah, in the steppe, in places devoid or almost devoid of tree vegetation. Back in the century before last, this idea was expressed by the French naturalist Jean-Baptiste Lamarck, who was the first to create a holistic theory of the evolution of the organic world, and the English naturalist Alfred Wallace, who simultaneously developed the theory of natural selection along with Darwin. However, one fact that Lamarck and Wallace could not have known, but their modern followers should know, makes this hypothesis extremely doubtful. The fact is that, as it turned out as a result of numerous studies conducted at the turn of the past and present millennia, the early hominids mostly lived not yet in the savannah, but in areas where tropical rainforests were preserved, or even dominated. Judging by the chemical composition of ancient soils, fossil plant pollen and the species composition of animals whose bones accompany the skeletal remains of the most ancient human ancestors, both Australopithecus and Ardipithecus and, moreover, their predecessors lived mainly in the jungle. Consequently, the transition to bipedality was not and could not be associated with adaptation to open landscapes. In addition, it is completely incomprehensible why, in fact, living in the savannah, you need to walk on two legs? After all, modern monkeys living in treeless areas (baboons, some populations of macaques) remain quadrupedal and do not seem to suffer from this at all. Both of these objections, by the way, fully apply to the once popular idea that hominids straightened up, allegedly due to the need to see farther and better navigate the savannah, where a good view was required to search for food and to detect danger in a timely manner.
Another explanation for the formation of upright walking, even more common than the previous one (however, it may well be combined with it), is the assumption that bipedalism was required to free the hands, which, in turn, was necessary for the manufacture of tools, and indeed gave man many important advantages over other animals (Fig. 5.1). This idea was often expressed already in the nineteenth century. It found its classical expression in the works of Darwin and Engels and was adopted by many later authors. "Man," wrote Darwin, "could not have attained to his present dominating position in the world without the use of hands which are so admirably fitted to serve for the accomplishment of his Will. ... But as long as the hands were regularly used for movement, they could hardly become perfect enough for making weapons, or accurately throwing stones and spears. ... For these reasons alone, it would be beneficial for a person to become bipedal ... ". At first glance, it is impossible to challenge the above arguments: what, in fact, could a person be without hands, and what kind of hands can a creature moving on all fours have? However, here, as in the previous case, the harmony of the proposed explanation is violated by some facts that became known only a century after the cited work of Darwin was published. First, judging by the archaeological data now available, the first stone tools appeared at least two, but rather three or even four million years later than the first upright hominids. Secondly, they made and used these tools, almost certainly, while sitting, so that the problem of freeing hands simply did not arise. Of course, it is more convenient to work at, say, a lathe or a carpenter's workbench while standing, but before that, the first hominids were still very far away. Those labor operations that were necessary and available to them are much easier to perform in a sitting position. In any case, this is exactly what great apes prefer to do when, for example, they crack nuts with heavy stones, and experimental archaeologists when they try to make tools from flint, bone, or wood, identical to those found during excavations.
By the way, it should be noted that the formation of bipedality in human ancestors, apparently, is not a unique event in the evolutionary history of hominoids. Ever since the middle of the last century, some researchers began to suspect that long before the appearance of the first hominids, upright monkeys already lived on Earth. The basis for such suspicions was given by the bone remains of Oreopithecus, who, judging by the geographical localization of paleontological finds, lived mainly in the south of the current Apennine Peninsula, in that part of it that was an island in the Miocene. A recent study of these materials by a group of Spanish and Italian anthropologists again confirmed that the Oreopithecus was not only able, but perhaps even preferred to move on the ground on two legs. This is evidenced by such signs as the bending of the lower spine in the anterior direction, the vertically located knee joint, as well as some structural features of the pelvis, which find analogies in the anatomy of Australopithecus afarensis. Moreover, it turned out that these hominoids, which became extinct 8 or 7 million years ago, also distinguished themselves by a hand structure that was not quite usual for monkeys. Sometimes it is even claimed that they could pick up and hold various objects with their fingers with such dexterity, which was later available only to people and their ancestors, starting with the Australopithecus. How the Oreopithecus used this quality of theirs - if they really possessed it 1 - is unknown. Maybe just to pick some small fruits from the trees and put them in the mouth, or maybe for some kind of action that would bring them even closer in our eyes to hominids. True, according to some important features, for example, in the structure of teeth, Oreopithecus are closer to lower apes than to anthropoids. They also could not boast of a large brain, as, indeed, of a large body size. According to available reconstructions, the average weight of these hominoids was approximately 30-40 kg. Nevertheless, the presence of clear parallels with the evolution of hominids is very interesting and makes us remember once again that nature had different development options in stock.
The transition to bipedality and the release of the forelimbs from the musculoskeletal function were also associated with the need to carry food and young, or signal with gestures, or scare away predators by throwing stones and sticks at them, and so on. However, all guesses of this kind are based on a clear exaggeration of the role of one-time, sporadic actions (throwing, gesticulating, carrying objects), which modern monkeys can easily cope with without changing their mode of movement. Chimpanzees, for example, are quite capable of putting a leopard to flight by brandishing thorny branches, or dragging heaps of heavy stones to places where there are many of their favorite hard-shelled nuts, then to use these stones as hammers and anvils. However, the fact that they are quite often forced to use their forelimbs as hands does not prevent them from being still, like millions of years ago, quadrupedal.
Much more interesting and perhaps more promising are those attempts to answer the "damned" question, where the emphasis is on finding the energy benefits provided by bipedal locomotion. The bioenergetic hypothesis explains the emergence of bipedalism by the greater energy efficiency of human bipedalism compared to the quadrupedal apes (Fig. 5.2). The main weakness of this explanation is that it invokes the advantages of upright posture, which could only come into play with fully developed human bipedalism, but which would be almost completely imperceptible in the process of its development, especially in the early stages of the transition. Even if bipedal locomotion, as known to modern humans, is indeed more energetically beneficial than quadrupedal locomotion (which, however, has not yet been fully elucidated), it does not at all follow that the same advantages were are also characteristic of the gait of early hominids. It, apparently, was very different from ours and was far from being as effective (more on this below).
Proponents of the thermoregulatory hypothesis saw the reason for the transition of our ancestors to bipedalism in the fact that the vertical position of the body during intense daytime activity in the hot savannah protected hominids from heat stress. Indeed, the surface area of the body exposed to direct sunlight is much less in an upright man than in a four-legged creature of the same size, and, as you can easily imagine, this difference increases as the sun approaches the zenith. However, as we now know, during the first million years of their history, erect-walking hominids lived mainly in the jungle, not in the savannas, and therefore they were no more threatened by heat stress than modern gorillas or chimpanzees.
To complete the picture, we can also mention the so-called "aquatic" hypothesis, according to which the orthogradeness of early hominids is the result of adaptation to life on the shelf, in the aquatic environment (Fig. 5.3). This idea was once actively discussed in pseudo-scientific literature, but among professional anthropologists, with a few exceptions, it did not have and does not have supporters. The reason for this is simple and lies in the fact that this hypothesis is based solely on assumptions of a semi-fantastic nature, not supported by absolutely any specific materials. There are no facts that at least indirectly indicate that the first members of the human clade “came out of the water”, unless, of course, we consider as such references, for example, to our ability to swim, which seems to be not inherent in chimpanzees, or to the fact that people have more thicker than other primates, a layer of subcutaneous fat.
Thus, it turns out that finding any specific benefits that could be associated with bipedality in its early stages of development is very difficult, if not impossible. A convincing reason for “the transition to orthograde locomotion has not yet been found,” and the beginning of anthropogenesis “melts in a shaky haze of uncertainties,” a prominent Russian researcher of human evolution admitted 15 years ago. 2 The situation has not changed since then. True, the number of hypotheses has increased markedly and continues to grow, but their number somehow does not turn into quality. Anthropologists, of course, do not lose optimism, hoping that the discovery of new bones and the improvement of methods for studying them will eventually provide an answer to the damned question, but these hopes can come true only if bipedalism really gave some benefits already to the first hominids. However, is it really necessary? What if there were no benefits?
1 There are doubts about this (Susman R.L. Oreopithecus bambolii: an unlikely case of hominidlike grip capability in a Miocene ape // Journal of Human Evolution, 2004, vol. 46, no. 1, p. 103-115).
2 Alekseev V.P. Anthropogenesis - a solved problem or a series of new problems? // Man in the system of sciences. M., 1989, p. 113.
Comparing the shape of the skeletons of two hundred organisms that have lived on Earth for the past 250 million years, with the corresponding genetic changes, anthropologist Aaron Filler of the Harvard Museum of Comparative Zoology and the Cedars Sinai Institute of Back Diseases proposed a new hypothesis for the origin of bipedalism. In his opinion, the ancient ancestors of people were able to straighten their backs as a result of a random mutation of the so-called homeotic gene, which is responsible for the formation of repeating elements in the embryo. Typically, such mutations lead to terrible deformities, such as arms and legs growing in place in the spirit of The Last King of Scotland.
However, it was precisely such a mutation that allowed one of the monkeys in the center of Africa to become the ancestor of the most perfect creature on Earth at the moment - man.
And it happened at least 20 million years ago.
The transition from four paws to two became possible due to the shift of the center of gravity back and down: to the sacral region and behind the spine. It has long been believed that this allowed them to maintain the balance necessary for a bipedal lifestyle, and, ultimately, to carry a disproportionately heavy head by the standards of the animal kingdom on their shoulders. However, the mechanism of this transition remained unclear.
The remains of the oldest known biped, the Morotopithecus bishopi, which are more than 20 million years old, helped to understand this issue. Discovered in Uganda back in the 1960s, the new species initially interested only narrow specialists. However, in 1997, paleontologist Laura McLetchi from Brooke University in New York proved that Morotopithecus was bipedal, and in 2006, its resemblance to possible human ancestors was revealed.
All classes of vertebrates fundamentally differ in the number and composition of all parts of the spine, reaching the highest development in mammals. Previously, Filler reported on the features of the vertebrae, or rather their processes, in upright. The transverse processes, to which the back muscles are attached, are “directed” forward in tetrapods.
In Morotopithecus, part of these processes turned back, and this allowed him, due to muscle tone, to at least partially straighten his back.
Other features of the bipedal skeleton, such as the attachment of ribs and curvature of the spine, appeared later as a means of compensating for load and facilitating movement. A similar structure and position of the body in space made it possible to develop not only the modern specialized shoulder girdle of great apes, but also the large brain region of the skull.
How an unusual mutation could have arisen is still unclear. The answer was found at the intersection of embryology, genetics and comparative anatomy.
Comparing data on the shape of the vertebrae and changes in the genes responsible for their formation, Filler traced the change in the supporting apparatus of vertebrates over the past 250 million years. And it turned out that most of the evolutionary leaps that had not previously had a clear justification are associated with mutations in the group of homeotic genes mentioned above.
In all animals, they are responsible for laying down repeating body segments in the embryo, such as the vertebrae and back muscles. Mutations in these genes lead to the most severe developmental anomalies, but, as it turned out, it was these mutations that played a key role in human development.
Failures in the inheritance of genetic information and natural selection have been considered for more than a century the main driving force of evolution, contributing to the development of organisms.
Surprisingly, in this case, the mutation caused rather a movement into the past - after all, the animal world had long since overcome the stage of walking on two legs. The most perfect animals of that time had been walking on four legs for many millions of years, and who could have known that for us this “mutation into the past”, usually incompatible with life, would turn out to be so important.
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