How chewing works
“What we showed is that by processing food, especially meat, before eating it, humans not only reduce the effort required to chew, but also chew it much more effectively,” notes Katie Zink, first author of the study and a member of the lab of Daniel Lieberman, professor of Biological Sciences at Harvard.
“What Katie did was creative but sometimes, frankly, a little stomach-churning at times,” Lieberman says. Not only did she have people come into the lab, chew raw meat and other foods and spit them out, but then she had to analyze the substances.”
To approximate the tenacity and texture of the prey that early humans ate, Zink and Lieberman, after much experimentation, focused on using goat, which the subjects chewed raw while Zink used instruments attached to their jaws to measure the effort involved.
“What we found was that humans can’t eat raw meat effectively with their low-crown teeth. When you give people raw goat meat, they chew and chew and chew, and most of the meat is still a big clump. It’s like chewing gum,” Lieberman describes. But once you started processing it mechanically, even if it was just cutting it up, the effects on chewing performance were dramatic.”
The introduction of this toothbrush in Europe was not until 1600, at the end of the Renaissance, when English merchants traveled to China and returned with them. The invention was not well received by Europeans because they considered the bristles to be too hard, which irritated their teeth and caused gum discomfort.
Although they began to be mass-produced, as in the case of the Williams Addis brushes, they did not have a good reputation, especially when, in 1723, it was discovered that the use of horsehair could cause oral diseases due to certain bacteria. The discovery was made by Pierre Fauchard, who also proposed the technique of daily rubbing of the teeth with natural sponges.
In the 19th century, it was the turn of Pasteur, who alerted dentists that brushes made with animal bristles generated bacteria and fungi. At that time, Pasteur made known the germ theory.
Today we can find toothbrushes with filaments of different hardness for patients in post-surgery periods, with periodontal disease or toothbrushes for orthodontic patients, prosthesis wearers and, in short, for hard-to-reach areas, among others.
Chewing is a part of the digestive function of mammals, including humans. It is the process by which previously ingested food is crushed at the beginning of digestion, thus increasing the amount of energy and nutrients obtained from the food compared to other vertebrates that do not chew. It is the process by which food is crushed with the help of the teeth and homogenized or lubricated by the teeth.
The process by which food is crushed with the help of the teeth and homogenized or lubricated with saliva, this is due to a congenital or unconditioned reflex action. The secretion of saliva is a response to direct stimulation of the taste cells or the buccal mucosa.
Saliva secretion also occurs in another way. The mouth waters at the sight of food or the smell of food, and even at the mere thought of food, especially when we are hungry. Pavlov’s experiments show that in the animal kingdom there is also a relationship between abstract concepts and salivary secretion in learned behaviors.
The history of masturbation describes the great changes in society in relation to ethics, social attitudes, scientific study, and artistic depiction of masturbation throughout the history of human sexuality.
Sexual stimulation of one’s genitals has been interpreted in a variety of ways by different religions, and has been the subject of legislation, social controversy, activism, and intellectual study within sexology. Social views on masturbation have also varied greatly in different cultures and throughout history.
From the earliest records, the ancient Sumerians had very relaxed attitudes about sex. The Sumerians widely believed that masturbation could increase an individual’s sexual potency, whether male or female, and often engaged in the practice alone or with a partner.  Men often applied pure oil, a special oil probably mixed with powdered iron ore, which was intended to improve friction. Masturbation was also an act of creation and, in Sumerian mythology, the god Enki had created the Tigris and Euphrates rivers, after masturbating and ejaculating into their empty riverbeds. Masturbation was also an act of creation and, in Sumerian mythology, the god Enki had created the Tigris and Euphrates rivers, after masturbating and ejaculating into their empty riverbeds. The Sumerians believed that masturbation could increase sexual potency.