I hope you had a very special Darwin Day on February 12. My honey and I spent it as a romantic evening watching some special videos. They gave me the urge to write about an intimate subject. The vids were about the current state of evolutionary theory, especially regarding us humans. And now I can’t resist my desire to write about itching.

Creationists talk about the amazing balance of physical laws that hold the universe together. Similarly, I would like to spread the Good News about the amazing balance that evolution has produced in our itching. Have you considered how natural selection would sculpt the perfect amount and distribution of itching? Itch too much and you could forage too little; maybe damage your skin. Itch too little, and who knows what kind of pestilence might hang on, partaking of your blood supply. You might even overlook a superficial infection that would be reduced by some abrasion; especially if you don’t have any knowledge of health or, for that matter, much of a conscious mind.

Speaking of consciousness, since the part of my brain that can talk is writing to yours, I’d like you to think for a moment of how you can feed data into a formula and turn it into a chart, or a shape. You have a visual representation of numbers. Now think of the statistical nature of natural selection. You could say that, in a sense, every animal is a representation of the statistics of selection pressures, and of the genes as being a handy data management program that comes replete with current data. Have an earthquake and a seismograph provides an analog and statistical readout. Have billions of years of natural selection and you get the latest animals — complete with survival-computed itching.

And if you think itching is always because of something actually going on at the site of the itch, think again. Stimulate the itch gene in the spinal chord of a mouse, and he starts scratching, which in turn inhibits the firing of itch neurons in the spinal cord. The itch gives you a glimpse into your most primitive origins. You have no idea how much you itch. It’s managed by primitive programming that has little use for your conscious mind. Just because you can pay attention to it is no reason to give your conscious mind credit for it or think you really know how much you scratch.

Of course, you can suppress it, but notice how intensely the demand commands you to satisfy that itch! What is that demand? Think of birds preening. What commands them to do that? If they had the will and tried to resist it, what overwhelming discomfort might well up? When people with obsessive-compulsive disorder try to resist their compulsions, they tell us they feel intense, irresistible anxiety and are driven to act on the compulsions. Theorists suspect that they have poor regulation of primitive impulses related to preening behavior. But they often have a conscious basis for their behavior; they justify it. Of course — people tend to justify unconsciously-driven behavior. They need to conform to social pressures.

Still need some proof regarding the unconscious nature of such urges? Obsessive-compulsive traits can be genetically loaded into animals. Researchers do this so we can better understand them. Stress sometimes causes obsessive-compulsive traits to emerge in humans and other animals, and this lends support to the idea that some kind of regulation has become unhinged, releasing instinctual forces.

To round out these ideas, I’d like you to notice how every area of you body needs a certain amount of vitamin S (scratch) every day. Then forget about it and let your unconscious continue to manage the affair, as it has all along.

As for the betterment of humanity, perhaps one day, we will be able to satisfy the itch without scratching. The motive: medical conditions that cause excessive, unnecessary itching.

Notes for Nerds

A study by Berkman and Plutzer found that only about 25 percent of high school biology teachers polled teach evolution in an adequate manner, as recommended by the National Research Council. They also found that roughly 13 percent of the teachers teach creationism or intelligent design.

Here are some details on evolution I’m throwing in from various sources just for fun (my way of saying no references from this point on).

The earliest human-like creatures emerged about 5 or 6 million years ago.

Most animals appeared as marine creatures around 542 million years ago, unless you believe some researchers that favor up to a billion years ago, but they have flimsy evidence.

Their ancestors were complicated cells with mullets, well, actually, flagella in the back. They did not bowl or have trailers.

Chimps and humans branched apart about 7 million years ago. But we have about the same number of genes. A number we also have in common with corn; about 25,000. Humans still like chimps and corn, but only name chimps, not cobs.

Different human species co-existed for a long time, dying out and leaving only Homo sapiens. Not all previous human species are our ancestors. They are separate branches on the evolutionary tree. The last was the Neanderthal, disappearing about 20,000 years ago. They and we branched off of a common ancestor about 400,000 years ago. Genetic data tell us that there probably was no interbreeding.

Our modern behavior has existed for only a small fraction of our existence. Most of our past casts us as stone-age folks with only the vaguest sense as to how to improve our lives (as in creating very primitive fireplaces in our caves, but we didn’t even fish). We didn’t shift into cultural overdrive until about 11,000 years ago, starting in Africa. This culminated in knockoff designer handbags.

There’s a theory that our brains are so big because a defect in our muscle genes gave us weaker jaw muscles, affecting how early our skulls fuse during development. I’m not joking. I saw it on PBS.

No one has determined the year of the first itch or scratch. But I’ll wager spontaneous itching (that does not stem from a parasite or other stimuli) came after we emerged from marine life and selection had plenty of time to develop it. The reason: fish only glance (dart against an object) or dive and roll (touching the floor) when there is a problem such as parasites. This is fortunate, as they have no arms.

References

Davidson, S., Zhang, X., Khasabov, S., Simone, D., & Giesler, G. (2009). Relief of itch by scratching: state-dependent inhibition of primate spinothalamic tract neurons Nature Neuroscience, 12 (5), 544-546 DOI: 10.1038/nn.2292

Berkman, M., & Plutzer, E. (2011). Defeating Creationism in the Courtroom, But Not in the Classroom Science, 331 (6016), 404-405 DOI: 10.1126/science.1198902

Sun, Y., & Chen, Z. (2007). A gastrin-releasing peptide receptor mediates the itch sensation in the spinal cord Nature, 448 (7154), 700-703 DOI: 10.1038/nature06029