Changes in Diet May Have Led to Humans Having Smoother Skulls

When a child is born, their brain is only a fraction of the size it will one day be. As many caregivers remember, an infant’s skull is flexible and made of bone and fibrous materials called sutures – colloquially called soft stitches. Smooth and flexible, a newborn’s skull is a masterpiece of evolution, allowing the brain to grow and develop like no other animal.

Zeray Alemseged, a paleoanthropologist in the Department of Organismal Biology and Anatomy at the University of Chicago, explains that human skulls gave our species an evolutionary advantage over others.

“Since we diverged from our cousins, the chimpanzees, about 7 million years ago, the hominid skull has changed dramatically,” Alemseged said. Discover.

Learn more: Viking skulls reveal that ancient people were robust, but not healthy

Why is the human skull smooth?

Throughout history, evolution has changed the appearance of humans. The brain casing, or the part of the skull that surrounds the brain, has expanded to allow more room for it. The face shortened, while the ridges and cranial structures that attach the large masticatory muscles disappeared as our need to eat tough meat dissipated.

Attachments to the powerful neck muscles, which were important to our primate ancestors, have also been greatly reduced over millions of years.

“In addition to the reasons mentioned above, the human skull is smooth because over the course of evolution we lost many of the ridges and ridges that were attachments for heavy chewing. [muscles]” said Alemseged. He adds that the main role of the human skull today is to house our exceptionally large brain, supporting the historically enlarged brain casing.

Protecting our brain

The structure of the human skull allows our brains to develop quickly after birth. At birth, the brain reaches about a quarter to a third of its total size, and doubles during the first year of life. By our fifth birthday, the brain will have reached approximately 90% of its adult size. Having a smooth skull could make it easier for the brain to grow after birth, Alemseged said. Discover. Because infants are born with unfused skull bones connected by “soft spots” or fontanels, their skulls allow room for this rapid growth.

This smoothness of the skull results from structural integrity and provides a uniform protective shell for the brain. According to the Cleveland Clinic, sutures separate the major bones that make up the skull, allowing brain space to expand.

When it reaches its maximum size, the sutures connect the bones like a quilt to form a strong bone. Five main sutures form the skull, such as the coronal suture, which runs horizontally from ear to ear. The lambdoid suture runs horizontally to join part of the back of the skull, while the metopic suture connects the frontal bone to the forehead. A vertical, sagittal suture runs down the top of the skull and, finally, the squamous suture connects the bones above the ears.

Development of the human skull and development of the monkey skull

The way a human infant’s skull develops is different from that of apes. Although the human skull has 22 bones as an adult, at birth it has many more distinct elements, making it particularly large compared to other parts of the body. Adult apes and gorillas generally have the same number of cranial bones, but that’s where the similarities end.

“The human skull is a primate skull, and the general configuration and components of the bones are similar to those seen in apes,” Alemseged said. “However, the human skull deviates from that of apes because of its exceptionally large brain, slender jaws, and tiny face, which make the human skull globular. In this sense, the human skull is so visibly different from that of other primates.”

Unlike humans, great apes have what Alemseged describes as a strongly built and very protruding face, with an equal ratio of facial size to skull size. The human face, on the other hand, is hidden under the skull, so reduced that, according to Alemseged, “we are almost faceless” compared to the great apes. At least in terms of size.

Learn more: Echolocation shapes a bat’s skull to match specific frequencies

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