The transition of hominids to bipedalism began from four to seven million years ago [1] [2] . This transition led to morphological changes in the human skeleton , including changes in the size and location of the bones of the foot , the size and shape of the hip and knee joints, the length and shape of the legs , and also the shape of the spine . There are several theories that explain the evolution of these changes [3] .
Content
- 1 Energy Efficiency
- 2 Skeleton changes
- 2.1 Stop
- 2.2 Hip
- 2.3 Knee
- 2.4 limbs
- 2.5 Skull
- 2.6 Spine
- 3 Consequences
- 4 See also
- 5 notes
- 6 Literature
- 7 References
Energy Efficiency
Homo erectus is 75% more economical in comparison with the movement of chimpanzees on both four and two limbs. Some hypotheses claim that this factor played a major role in the transition to upright posture [4] .
Skeleton Changes
Foot
The transition to upright posture led to the development of an increased calcaneal part of the foot, which is necessary to maintain balance when walking and maintain increased body weight [5] . The shape of the foot also changed: the big toe , located at the early hominids as well as on the hands, changed position, standing in line with the other fingers [6] . In addition, the arch of the foot was formed, in contrast to the flat feet of other hominids [6] . All these changes contribute to energy savings during movement [1] [7] .
Hip
The human hip joint is significantly larger [ clarify ] than that of hominids, which provides support for a larger body [6] . These [ what? ] changes brought the spine closer to the pelvis, which increased stability during upright posture [8] and reduced energy consumption for maintaining balance when walking [6] [1] [9] .
The shape of the ilium has changed from long and narrow to short and wide, with the wings of the ilium spaced horizontally. Together, these changes provide an increase in the area of attachment of the gluteal muscles, which helps to stabilize the torso when standing on one leg. The sacrum also increased in width, which led to an increase in the diameter of the birth canal and facilitated childbirth . The sciatic bones increased, which improved the fastening of the ligaments supporting the abdominal cavity during upright posture [10] .
Knee
The knee joints have increased for the same reason as the hip joints, namely, to maintain increased body weight [6] . The extension angle of the knee (the angle between the thigh and lower leg formed when walking) decreased. Changing the shape of the knee joint allowed to reduce the energy loss due to the vertical movement of the center of gravity during movement [1] [6] .
Limbs
The increase in leg length with the development of upright posture led to changes in muscle function. The effort required when walking is transmitted from the muscles of the legs through the ankle . Long legs allow you to use the natural vibrational movement of the limbs when walking, therefore, additional muscles are not required to move forward the other leg for the next step [6] .
The upper (front) limbs, excluded from the process of movement, were modified in such a way that it became possible to use them to hold objects and delicate manipulations with objects [11] . This led to a decrease in the relative strength of the upper limbs of a person compared to other hominids [12] [13] [14] . With the transition to upright posture, the role of the gluteal muscles increased, becoming one of the largest muscles in the human body. In chimpanzees, these muscles are much smaller, which proves the important role of this muscle group in upright posture. Buttocks also prevent the body from tipping forward while running [9] .
Skull
The human skull is balanced on the spine: the large occipital foramen is located in the lower part of the skull, which carries a significant portion of the head weight back. In addition, the flat shape of the human face helps maintain the balance of the skull on the occipital condyles , which makes it possible to maintain the head without additional muscles and developed superciliary arches observed in anthropoid apes. As a result, a person’s forehead muscles are used exclusively for facial expressions [11] .
An important role in human evolution was played by an increase in the size of the brain, which began about 2.4 million years ago [approx. 1] . The brain reached modern sizes no later than 500 thousand years ago. As a result, the human brain is three to four times the size of the brain of the nearest evolutionary predecessor - chimpanzees [10] .
Spine
With the transition to upright posture , the human spine received a double bend: the upper (thoracic) section is bent back, and the lower (lumbar) section is forward. Without lumbar flexion, the spine would constantly lean forward, which would require much greater muscular effort to maintain balance [8] . The presence of a double bend places the projection of the body's center of gravity directly between the feet [6] , which saves energy when walking [1] .
Consequences
Even taking into account numerous morphological changes, the human skeleton still remains poorly adapted for upright posture, which leads to numerous diseases of the musculoskeletal system [15] . So, a large number of people with age begin to have problems with the lumbar spine and knee joints: according to some reports, lower back pain is the leading cause of lost work days [16] . Arthritis became a problem right after the transition of hominids to upright posture: scientists found its traces in the vertebrae of prehistoric hunter-gatherers [16] [approx. 2] . Further changes in the joints, which could correct the situation, are impossible due to a contradiction in the requirements of stability and efficiency of movement [6] .
See also
- Vertebral displacement
Notes
- Notes
- ↑ According to recent research, the development of hominid brain was caused by the need to adapt to global climate change.
- ↑ , a specialist in forensic anthropology from the University of Pennsylvania in his book Scars of Human Evolution (1951), was the first to suggest a connection between spinal diseases and upright .
- Footnotes
- ↑ 1 2 3 4 5 Kondō, Shirō (1985)
- ↑ Staff (August 14, 2016)
- ↑ Kwang Hyun, Ko (2015).
- ↑ Rodman, Peter S .; McHenry, Henry M. (1980).
- ↑ Harcourt-Smith, WEH; Aiello, LC (2004)
- ↑ 1 2 3 4 5 6 7 8 9 Aiello, Leslie and Christopher Dean (1990)
- ↑ Latimer B, Lovejoy CO (March 1989)
- ↑ 1 2 Wang W, Crompton RH, Carey TS, et al
- ↑ 1 2 Lovejoy CO (November 1988)
- ↑ 1 2 Wittman, Anna Blackburn; Wall, L. Lewis (2007)
- ↑ 1 2 Saladin, Kenneth S. (2003). 3rd, ed
- ↑ Ruff Christopher (October 2003)
- ↑ Thorpe SK, Holder RL, Crompton RH (June 2007)
- ↑ Saladin, Kenneth S. “Chapter 8.”
- ↑ Taylor, 2016 , p. 114.
- ↑ 1 2 Jacob C. Koella; Stearns, Stephen K. (2008)
Literature
- Jeremy Taylor Darwin Health: Why We Get Ill and How It Tells Evolution = Jeremy Taylor “Body by Darwin: How Evolution Shapes Our Health and Transforms Medicine”. - M .: Alpina Publisher, 2016 .-- 333 p. - ISBN 978-5-9614-5881-7 .
- Grabowski MW, Polk JD, Roseman CC Divergent patterns of integration and reduced constraint in the human hip and the origins of bipedalism. (English) // Evolution : journal. - Wiley-VCH , 2011 .-- Vol. 65 , no. 5 . - P. 1336-1356 . - DOI : 10.1111 / j.1558-5646.2011.01226.x . - PMID 21521191 .
- Crompton RH, Sellers WI, Thorpe SK Arboreality, terrestriality and bipedalism. (neopr.) // Philos Trans R Soc Lond B Biol Sci .. - 2010 .-- V. 365 , No. 1556 . - S. 3301–3314 . - DOI : 10.1098 / rstb.2010.0035 . - PMID 20855304 .
Links
- Human Timeline (Interactive) - Smithsonian (August 2016).