The Evolutionary Origins of Hiccups and Hernias

[Elderberry]

It's the 150th Anniversary of Darwin's Theory of Evolution and Scientific American has dedicated this month's entire issue to the topic.

Here's one of many interesting articles from that issue. Hope some of you enjoy reading it.

JK

The Evolutionary Origins of Hiccups and Hernias

How biological hand-me-downs inherited from fish and tadpoles evolved into human maladies
By Neil H. Shubin

I started teaching human anatomy at the same time my university renovated my laboratory. As it turns out, this coincidence could not have been more propitious. Teaching anatomy for the first time can be a struggle, and it is not just because there are an enormous number of names to learn. A glimpse inside the body reveals structures left inside of us during the course of evolution, which often seem a confused jumble, with arteries, nerves and other structures taking odd paths to get from one part of the body to another.

While I was struggling to understand the body’s internal structures, I was given space in a 100-year-old building that needed to be renovated into a modern laboratory. When we opened the walls to look at the plumbing, wiring and other mechanicals, we saw a tangle that made no apparent sense; cables, wires and pipes took bizarre loops and turns throughout the building. Nobody in their right mind would have designed my building to conform to the snarled mess we saw when the wall was removed. Constructed in 1896, the utilities reflect an old design that has been jury-rigged for each renovation done over previous decades. If you want to understand the twisting pathways for a cable or a pipe, you have to understand their history and how they have been modified over the years. The same is true for structures in the human body.

Take the male spermatic cord. This tube connects the testes, in the scrotum, to the urethra, in the penis. In so doing, it forms a path for sperm to exit the body. The scrotum lies adjacent to the penis, so you would think that the best design would take the shortest course, a straight shot between the two structures. Not so. The spermatic cord ascends from the scrotum, then loops inside the pubic bone, descends through an opening below the hip joints and finally travels to the urethra inside the penis. This path—a historical legacy—is as much a source of vexation for medical students to understand as it is for the human males who suffer certain kinds of hernias because of it.

Piscine Inheritance
To make sense of our own bodies, we need to examine the history we share with everything from microbes and worms to fish and primates. In the case of the spermatic cord, human gonads begin development in a similar way to those of sharks, fish and other bony animals. The gonads—ovaries in females and testes in males—originally form high up in the human body, near the liver, presumably because the interactions between the tissues that develop into the gonads occur there. In adult sharks and fish, the gonads typically remain up near the liver. They probably stay in this ancestral configuration because their sperm can develop within the confines of the body cavity itself.

Mammals like us do things differently from our fish ancestors. As a male fetus develops, the gonads descend. In females, the ovaries move down from the midsection to lie near the uterus and fallopian tubes. This movement ensures that the egg does not have far to travel to be fertilized. In males, the gonads descend farther, all the way to the scrotal sac, which extends from the body.

This feature is quite important for the production of healthy sperm. One possible reason is that mammals are warm-blooded and that the quantity and quality of sperm are dependent on developing in a cooler temperature than the rest of the body. Indeed, one study even suggests that a shift from tight-fitting jockeys, which can press the scrotum against the body, to boxers, which allow it to dangle, can improve some factors of sperm quality. Accordingly, the mammalian scrotum is a sac separated from the warm body that can rise and fall to control the temperature at which the sperm develops—think “cold-shower effect.â€

[gyre]

Any origin for photopic sneezing?

[Elderberry]

Any origin for photopic sneezing?

I don't know; but my guess would be that there is. If I have some time later maybe I'll try and do some research on it.

JK