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4.6. Human evolution: process of hominization

Human evolution

We humans, along with other animals, belong to the Metazoan kingdom. We have all become who we are today through the same biological and evolutionary processes. The environmental changes that have occurred in the environment, mutations, and natural selection caused some populations of primates to be transformed to give rise to hominids. Humans are the most evolved hominids. All this long process of evolution that has occurred until modern humans have emerged is called hominization.

The humanization occurred as a result of environmental change in eastern Africa. The lack of rain caused many trees to disappear and the vegetation was reduced to the existing savannah. The primates, from which man arose, had to adapt to the hot and dry environment.

The first hominids appeared approximately five million years ago. Hominids are characterized by:

  • Have your position upright.
  • Be biped.

Bipedalism

The bipedalism, or upright position is the ability to walk on both lower extremities without supporting palms and knuckles, gaining upright position.

Bipedalism could arise when some groups of primates, due to a change in the climate produced about 15 million years ago that made many trees disappear, had to abandon their arboreal life.

Having an upright position allowed them to locate prey and predators, since they could see around them more easily. Furthermore, by not using their hands, they could use them for other purposes.

The bipedalism took other associated morphological changes in the skeleton and musculature:

  • The spinal column stops being straight to take the shape of an "S". This way, it better supports the upright posture and keeps the center of gravity above the waist and that the feet bear the weight. Bipedalism puts a lot of stress on the spine, so it is not uncommon for us to have back pain.
  • Narrowing of the pelvic canal, making it difficult for women to give birth . Human childbirth is more painful than that of other primates.
  • Shortening of the upper extremities, which cease to have a locomotor function.
  • Modification of the skull to adapt to the upright position. The hole in the skull through which the spinal cord passes, the foramen magnun, moves to the base of the skull. The skull goes from being inserted in the spine at the back to doing it at the bottom. Thanks to this change in the insertion of the spinal column in the skull, changes occurred in the larynx that have allowed the vocal cords to develop and we have the ability to speak. Language allowed the coordination of groups and the transmission of knowledge, allowing cultural evolution and symbolic thinking.
  • The appearance of an opposable thumb makes it possible to grasp and manipulate objects.
  • The feet become less flexible, with the sole arched to distribute the weight more evenly. The thumb is wider and not opposable to the rest of the fingers, since it is only used to walk.



Advantages of bipedalism

Despite the fact that being bipedal places great stress on the spine and the narrowing of the pelvic canal, bipedalism has more advantages than disadvantages, such as:

  • It allows you to leave your hands free, since they are not used to move around, so they can be used to pick up objects.
  • By having their eyes higher, they can see the horizon above the vegetation to find prey or flee from predators.
  • The bipedal movement is slower than the quadruped, but since it consumes less energy it allows it to travel long distances. Because it takes less energy to survive, they need less effort to feed.

Other changes in hominization

The evolution of hominids has also produced other changes:

  • Increased cranial capacity. The australopithicus had a cranial capacity of about 500 cm3, which increased with the process of humanization to 1000 cm3 of the Homo antecessor, 1500 cm3 of the Homo neanderthalensis , or modern humans who are between 1200 and 1850 cm3 of cranial capacity.
  • Brain development. It allows you to make tools, among many other things.
  • Changes in the shape of the skull. The jaw becomes less prominent, and the brow ridges less marked. The frontal bone becomes more vertical, appearing the characteristic human forehead. These changes made the skull lighter and increased in size.
  • The body hair almost completely disappeared, remaining only on the hair on the head and on the hair that appears as secondary sexual characteristics from puberty on some parts of the body.
  • Changes in teething, which adapts to an omnivorous diet. The number of teeth is reduced from 36 to 32 current teeth. The canines (fangs) become smaller, similar to the rest of the teeth. The premolars and molars also decrease in size.