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Outside magazine, August 1995

By Patrick Clinton

I hear that scientists have decided that mushrooms are animals. Am I missing something?
Nick Fortna, Chicago, Illinois

In 1993, a team of molecular biologists was trying to construct an evolutionary family tree of all living organisms by analyzing ribosomal RNA. The study revealed something surprising: Fungi and animals shared a branch. On the great tree of life, in other words, mushrooms turned out to be our brothers, while plants are only our cousins. "There is some organism that lived a billion years ago that was the ancestor of all animals and all fungi," says biologist Mitchell Sogins, one of the study's authors. Go back even further and we find the ancestor of that organism and plants. Go back even further and, as Sogins puts it, "everybody's unicellular."

The similarities between animals and fungi are striking enough that some scientists study human neurology by examining yeasts. And it's believed that fungal skin diseases are hard to treat because, on the molecular level, they resemble human tissue. So maybe it's time to start thinking of athlete's foot not as an infection, but just another relative who won't leave.

Why does scat stink? You'd think it would draw predators--an evolutionary disadvantage.
Julian Holmes, Denver, Colorado

Sure, smelly droppings can let a predator know that prey is in the neighborhood. But they can work the other way too: Herbivores, for instance, are extremely sensitive to the sulfur compounds present in carnivore droppings. The predator-prey thing, however, is really just an incidental issue here, for scat stench serves a far more important role in the wild.

What you need to understand is that, when it comes to communication, animals do it with dung. Scat is an almost universal mode of discourse among animals of the same species, transmitting information about territory, feeding strategy, and the like. "Most mammals other than people are far more inclined to use chemical cues to communicate than other kinds of displays," says Russ Mason of the Philadelphia-based Monell Chemical Senses Center, a kind of think tank of smell.

Consider your dog on his morning walk. When he pauses to check out another dog's calling card, he's involved in a fairly detailed act of social intercourse, learning what competitors or eligible mates have been around, what's been on the menu--important stuff. It's like he's reading the newspaper. Had the scat been scentless, your dog might have missed it altogether. And, really, what good is an uninformed pet?

Why are oceans salty?
Lucy Wood, Nairobi, Kenya

When rainwater falls on the ground, much of it drains via creeks and rivers toward the sea. Along the way, it picks up salts from the rocks and soil. Thus rivers become progressively saltier as they head downstream. For example, by the time the Mississippi River nears the Gulf of Mexico, its salt content has swelled to about two parts per thousand.

All of these salts are dumped in the ocean. And here's the trick: When seawater evaporates, the salt stays behind. Some ends up in sediment on the ocean floor. The rest stays in solution and gives surfers perfect complexions.

Why aren't lakes salty? Because most of them drain. But landlocked lakes, especially in hot, dry climates, can get mighty briny. The Great Salt Lake clocks in at 240 parts per thousand, compared to only 35 for the oceans.

Although the whole rain-and-drain process has been going on since your sister was a fungus, we're in no danger of a terrestrial salt shortage: There should be enough in the ground (sodium being the seventh most common substance in the earth's crust) to keep the cycle going another billion years.

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