Vestigial Organs Not So Useless After All, Studies Find

[Oski]

Appendix, tonsils, various redundant veins—they're all vestigial body parts once considered expendable, if not downright useless.

But as technology has advanced, researchers have found that, more often than not, some of these "junk parts" are actually hard at work.

Case in point: the spleen, which a new study shows may be critical in healing damaged hearts.

Sure, the spleen—kidney shaped and tucked into the upper left of your abdomen—helps spot infections and filters out red blood cells that are damaged or old. But overall the organ has been seen as nonessential. Cut it out, and people still live.

But the new study, to be published tomorrow in the journal Science, has uncovered another, more critical role.

How Do You Mend a Broken Heart?

Researchers studying mice discovered that the spleen stores monocytes, white blood cells essential for immune defense and tissue repair.

Previously, scientists had thought monocytes were made only in bone marrow, like other types of white blood cells, and were "stored" in the bloodstream.

But the new study found that the spleen contains ten times as many monocytes as blood—making it a far more important storehouse.

What's more, the spleen is the source of 40 to 50 percent of the monocytes involved in nursing lab mice back to health after a heart attack, said study co-author Filip Swirski of Massachusetts General Hospital's Center for Systems Biology in Boston.

"If you're going to survive a heart attack, your heart has to heal the proper way, and that depends on monocytes," Swirski said.

"It was thought that the monocytes that accumulated immediately after a heart attack were ones that had been circulating in the blood. But we did calculations and found that the number that accumulated in the heart far exceeded the number in circulation," he said.

"And in studies where we removed the spleen and then induced a heart attack, we saw a vastly fewer number of monocytes accumulate."

Simply put, mice without spleens weren't able to recover as well.

Neither, it seems, can humans without spleens.

A 1977 study, published in the medical journal The Lancet, followed the health of World War II veterans over 20 years—some with spleens and some who'd lost theirs to war injuries.

The spleen-less men were twice as likely to die from heart disease and pneumonia.

"They knew the spleen played an important role, but they didn't know how," Swirski said.

Dangerous Logic

None of this is surprising to Jeffrey Laitman, director of anatomy and functional morphology at New York City's Mount Sinai School of Medicine and president-elect of the American Association of Anatomists.

History is littered with body parts that were called "useless" simply because medical science had yet to understand them, Laitman said.

"People say, You can remove it and still live. But you have to be careful with that logic," he said. "You could remove your left leg and still live. But whenever a body part is moved or changed, there's a price to pay."

Appendix Rescued From Biology's Junk Heap

In some cases, life in the developed world—rather than insufficient medical technology—has obscured important functions of vestigial organs.

The appendix, a narrow tube that hangs off one end of the colon, is probably the most famous "junk" organ. But it's turned out to be important even today—in certain circumstances.

"It's hard to figure out what the appendix does when you're studying superclean animals and people," said Bill Parker, assistant professor of surgery at Duke University Medical Center and one of the researchers who exposed the appendix's secrets in a 2007 Journal of Theoretical Biology study.

Far from useless, the organ is actually a storehouse of beneficial bacteria that help us digest food (interactive digestive-system guide).

The appendix evolved for a much dirtier, parasite-plagued lifestyle than the one most people live in the developed world today, Parker said. But where diarrheal disease is common, for example, the appendix is apparently vital for repopulating intestines with helpful bacteria after an illness.

Another example of anatomy lagging behind lifestyle, according to Mount Sinai's Laitman, is collateral circulation. Certain systems of veins and arteries ensure blood flow when the main paths are blocked or damaged.

The systems appear to be truly vestigial, at least for now.

Elbows, knees, and shoulders, for example, all have collateral circulation, Laitman said, but the heart and much of the brain don't.

"Why would we adapt enormous redundancy in an elbow but not where it really matters?" Laitman said. "The answer is unsettling. When do we have strokes and heart attacks? Our 50s, 60s.

"When the blueprints for our species were being drawn up, nobody lived that long."

The fact that our bodies evolved while humans lived short lives hunting and gathering is one key to understanding many "useless" body parts, Laitman said.

From an evolutionary viewpoint, we've been living in the modern manner for a relatively short time, he pointed out. "Our circumstances have changed a lot, but our bodies haven't."

http://news.nationalgeographic.com/n...al-organs.html

[Sigurd]

From an evolutionary viewpoint, we've been living in the modern manner for a relatively short time, he pointed out. "Our circumstances have changed a lot, but our bodies haven't."

Indeed - considering that our bodies have not yet fully become accustomed to an agricultural diet after slightly over 10,000 years ... it is no surprised that many organs have not yet fully become accustomed to a cleanly lifestyle, something which we only know for a few centuries.

So obviously quite a few body parts do a lesser job, but they are still vital to survival in extreme situations we may find ourselves in ... and might still be useful in future days when we all live in less friendly circumstances. Perhaps evolution knows that option and is particularly slow in changing some of these otherwise vital parts?