Strange but true: Not all dog noses are black

Published: Thursday, Sept. 21 2006 12:00 a.m. MDT

Question: Why do dogs have black noses?

Answer: Some don't, like a weimaraner or vizsla whose nose matches its silver or red coat color, says "New Scientist" magazine's "The Last Word." In fact, many puppies start out with pinkish noses that only later darken. One genetic pressure toward black is protection against sunburn, affecting both dogs and cats in areas not fur-protected. Pink-nosed dogs, hairless breeds and dogs with very thin hair on their ears need to be protected with sunscreen. Another pressure is dog breeders' long-standing preference for black in noses, an aesthetic consideration that applies selective influence in pedigree dogs, "adding a bit of human-directed evolution."

Question: If your two eyes are of different colors, then you probably already know the term for this rare condition. Does it have any special significance?

Answer: Called "heterochromia iridium," famous examples reportedly are Jane Seymour (one green iris, one brown) and Dan Aykroyd (blue, brown). Kate Bosworth is said to have partial heterochromia—meaning two different colors in the same iris—with two blue eyes but a hazel section at the bottom of one. Heterochromia can be genetic or caused by eye disease or injury. So check with a doc in any case, and certainly check if an eye suddenly starts changing colors.

But don't worry if your dog, cat or horse exhibits heterochromia, since it's quite common in these species.


Send STRANGE questions to brothers Bill and Rich at strangetrue@compuserve.com, coauthors of "Can a Guy Get Pregnant? Scientific Answers to Everyday (and Not-So-Everyday) Questions," from Pi Press.

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