Human beings are composite creatures. We’re mostly made of carbon, oxygen and hydrogen, stuff that’s naturally abundant on Earth, but we’ve also got bits of iron and other heavier elements that aren’t so easy to synthesize. Those things come from beyond the black, born in supernova explosions and rained down on our world like building blocks from Heaven. Acknowledging that we are literally made of starstuff, Carl Sagan often remarked that people are a way for the universe to understand itself.
But what of those instances when there’s nothing to figure out? A common theme in this column is trying to determine what really makes a man. Of course it’s mostly our DNA, and the microscopic critters crawling on and in us play their role, but there’s also a lot of useless crap kicking around that nobody needs. Kind of like the garage of a retiree. A life of hard work bought him a turbocharged sports car, but it’s surrounded by tools he doesn’t use anymore, a broken weedeater and a stack of newspapers from 1973.
Man is an impressive feat of engineering, but he clearly wasn’t built from the ground up. There’s much wonder in finding the function of our practical parts, but we can’t ignore the pieces that just don’t fit. Part of what makes a man are the vestiges that no longer serve a purpose and the junk that’s just along for the ride.
It Used to Work
Some of the clunkers that clog up our physiology are so-called “vestigial” structures that have outlived their usefulness. Vestigiality is rampant throughout the animal kingdom, and actually serves as great evidence for evolution and the interconnectedness of all life. Why else would snakes be hiding the remnants of hip bones, from before they traded their legs for greater maneuverability, or cavefish display non-working eyes? Dolphins and whales even have the genes for odor recognition, calling back to their land-based origins, even though not one species currently has a sense of smell.
Humans aren’t immune to the biological clutter. The most famous example is the vermiform appendix, something no one would even talk about if it didn’t get infected in some people and cause massive abdominal pain. While its sole function these days is to take up space and leave a cool scar when removed, its original purpose is uncertain. The appendix’s tendency to act as a bacteria trap may in fact be a clue, though. While it was once thought to have aided in the digestion of tough plant material thousands of years ago, the prevailing guess as of late is the appendix served as a repository to reintroduce your natural gut flora after a bout of dysentery, which was so common in those times as to almost be routine.
Really just sits there at the end of your colon, waiting to cause trouble.
Other examples include the coccyx, a tailbone for an organism that jettisoned its tail, and occasional occurrences of the vomeronasal organ, which detects pheromones in lower primates but doesn’t seem to have the necessary neural connections to work in us. Some believe that’s an ability we lost to accommodate our spectacular color vision, though that hypothesis has come under fire recently.
It Never Worked… Right?
The myth that humans only use 10% of our brains is demonstrably false, but could 98% of our genetic make-up be idle trash? That overwhelming amount technically called “noncoding DNA,” as it doesn’t do the molecule’s usual job of encoding protein sequences, is sometimes colloquially referred to as “junk DNA.” Such superfluous sequences are sometimes looked at as genetic parasites, moving around and “transposing” to avoid deletion, and might even lead to cancer progression. Some of it is obviously not there to help us, being conferred into our nuclear material by sneaky retroviruses looking to keep their own lineage alive by piggybacking on something successful.
“I’ll just slip this in there… you’ll never even notice.”
It’s clear that at least a portion of that muddle is indeed important, acting as “switches” that govern gene expression. The famous ENCODE project proclaimed last year that as much as 80% of junk DNA could be ascribed such functions, though the study has received much criticism. A paper published in May shows that at least one plant does fine without all the jumble, so it may not be so necessary. But then why is four fifths of the genetic material we have in common with mice supposed “junk?” Why has it been preserved in both groups for 70 million years, since our last common ancestor? Whether the bulk of noncoding DNA actually matters or if it’s the cellular equivalent of a passenger seat full of parking tickets and cheeseburger wrappers is a contentious, ongoing debate.
It Doesn’t Work, But it Sure is Pretty
The great popularizer of evolution Stephen Jay Gould and geneticist Richard Lewontin put a burr under a lot of their colleagues’ saddles when they introduced the idea of biologic “spandrels” in 1979. Until then, most were convinced that all an organism’s features were naturally selected and therefore conveyed some kind of advantage. Gould and Lewontin argued that some things were just unintended consequences of legitimately beneficial adaptations and served no purpose themselves, like the space between an arch and its overlying dome in Renaissance architecture. Sculptors of the time utilized that “useless” space for art, and aesthetic value can be found in the phenotypic analog, too. There’s not much reason for blood to be red, other than that’s what hemoglobin has to look like, but slasher movies would be a lot less colorful otherwise. The existence of spandrels can be further confirmed in recently domesticated Russian breeds of foxes, which were bred solely to be made more tame, but also ended up with floppy ears and curved tails, like dogs.
What a cute, recently rehabilitated killing machine
Another unnecessary “just so” feature may be the hymen. It seems to serve no purpose but resembles a similar membrane that covers the mouth during embryonic development. That one’s perforated before birth, though. Even the female orgasm may be unintended, as the phenomenon is really only reproductively important for men, and the clitoris is a would-be penis that escaped an in utero testosterone bath. I wouldn’t use that as an excuse to leave your lady hanging, though. “Your orgasm isn’t evolutionarily adaptive” is probably not a persuasive argument at that moment.