Greasy Fingers and Evolution

I just posted a YouTube video on this topic. [https://youtu.be/lItwjRfxP7A ].

Much has been speculated and written about the evolution of human intelligence in all of its manifestations, including speech and tools. There is no reason that many of these ideas could not simultaneously be true.

One idea is that tool-making and intelligence evolved together. At first, a rudimentary form of human intelligence—the ability to envision how a rock could be made into a tool—was necessary to get the process started. Then, as stone tools, then spears and arrows and atlatls, became more sophisticated, a much higher level of intelligence was required. Even sexual selection was involved, with the idea that men invented better and better tools to impress their prospective mates.

It is impossible to think about human evolution without considering the origin of speech. Even the ability to make the sounds of which words are composed had to evolve. An evolutionary change in the larynx allowed a greater range of vowel sounds. And the evolution of dexterity of lips and tongue was necessary for consonants. Some have speculated that the ability to use the lips in speech (and for kissing) evolved from the ability of infant mammals to purse their lips around the mother’s teat.

All of this required an exponential increase in human intelligence, which was possible when more calories and nutrients were available for the growth and maintenance of the human brain. Human intelligence exploded when our ancestors began to cook their food, allowing a greater amount of nutrition to be available from the same amount of foraged or hunted food.

All true, but as I was eating greasy pieces of poulet rôti the other day, I realized yet another possible reason that human lips and tongues evolved dexterity. It is not enough to just capture and cut animals as food, or to cook them for nutrition. There is also an advantage to being able to get every last little morsel of meat from the bones of the cooked prey. An early human could get a great deal of meat from big pieces of cooked meat. But there was also an advantage to eating the little bits of meat hiding among the joints.

Those little bits of meat could provide just enough extra calories and nutrients to make a difference—slight, but significant—in production of offspring. Over time, the bits of meat and fat wasted by hominids with slightly less dexterity of lips, tongues, and teeth might give an advantage to the hominids who could glean the meat and fat more carefully. Of two tribes, both of which cooked their meat, the one with greater motor skills in their fingers and nibbling ability will get more benefit from their food than a tribe that threw a lot of perfectly good morsels of meat and fat on the bone heap.

It could also give an advantage within a group of hominids. A hominid that could say, “You done with that bone? There’s a lot of good meat and fat still on it,” might prevail over the hominid that handed the bone to him.

At least, this is what I was thinking as I ate every little bit I could get from the roast chicken. Think of that the next time you throw away a chicken leg with lots of good calories still on it.

In Praise of Bitterness

In the general biology labs that I teach, the students map out which portions of their tongues can taste sweet, sour, salty, and bitter chemicals. Of course, they hate the bitter quinine.

The ability to taste bitter compounds, and to dislike them, is of immense importance to our survival today as it has been throughout animal evolution. Most bitter compounds are potentially toxic, and if we taste something bitter, we may need to stop eating it so quickly that disgust, rather than rational decision, is necessary.

One student, however, was unable to taste the quinine. I never found out if he could taste any other bitter compounds. This is not a good thing for him. He has to be extremely careful about what he consumes.

According to a genetics website at the University of Utah, “Humans have about 30 genes that code for bitter taste receptors. Each receptor can interact with several compounds, allowing people to taste a wide variety of bitter substances.” This is because a wide variety of different molecules can be toxic. Many medicines are toxic in large quantities, and taste bitter even in small quantities; and these medicines are not chemically similar to one another. The ability of the human tongue to detect “bitter” is actually thirty different abilities. In this way the human brain has a single response—“This is bitter, don’t eat it”—to a great variety of potential threats.

Next time you taste something bitter, think about this and feel a little gratitude to your nervous system for protecting you.