Tuesday, May 9, 2006

Dolphins Whistle One Another's Names

Bottlenose dolphins can call one another by name when they whistle, making them the only animals besides humans known to recognize such identity information, scientists reported yesterday.

Scientists have long known that dolphins' whistling calls include repeated information thought to be their names, but a new study indicates that dolphins recognize these names even when voice cues are removed from the sound.

A dolphin might be expected to recognize its name if called by its mother, but the new study found that most dolphins recognized names -- their signature whistles -- even when emitted without inflection or other vocal cues.

More than that, two dolphins may refer to a third by the third animal's name, said Laela Sayigh, one of three authors of a paper published in the Proceedings of the National Academy of Sciences.

In nine out of 14 cases, the dolphin would turn more often toward the speaker if it heard a whistle that sounded like a close relative's.

Short-Term Use Of Estrogen Low-Risk

Women who take estrogen-only pills for at least 15 years run a markedly higher risk of developing breast cancer, according to a study of nearly 29,000 nurses. But no increased danger was found among those who took the hormone for less than 10 years.

Researchers said the findings should be reassuring for women who want to use estrogen for a short time to relieve menopausal symptoms.

Hormone supplements were once thought to help postmenopausal women postpone age-related ills. But the government's Women's Health Initiative study in 2002 contradicted those beliefs for estrogen-progestin supplements, finding an increased risk of breast cancer, stroke and heart attack.

The new findings came from the less-rigorous but longer-running Nurses' Health Study.

For women who had been on estrogen for at least 15 years, the risk of hormonally driven breast cancer (the most common type) climbed 48 percent. At the 20-year mark, the risk of any type of breast cancer rose 42 percent.

"This says at least for the shorter-term users, you don't need to panic" about breast cancer, said lead author Wendy Chen, an oncologist and epidemiologist at Brigham and Women's Hospital and the Dana-Farber Cancer Institute in Boston.

Lesbians' Brains React Like Straight Men's

Lesbians' brains react differently to sex hormones than those of heterosexual women.

An earlier study of gay men also showed their brain response was different from straight men -- an even stronger difference than has now been found in lesbians.

Lesbians' brains reacted somewhat, though not completely, like those of heterosexual men, a team of Swedish researchers said in today's edition of the Proceedings of the National Academy of Sciences.

A year ago, the same group reported findings for gay men that showed their brain response to hormones was similar to that of heterosexual women.

The findings support the idea that homosexuality has a physical basis and is not learned behavior.

The team led by Ivanka Savic at the Stockholm Brain Institute had volunteers sniff chemicals derived from male and female sex hormones. The chemicals are thought to be pheromones -- molecules known to trigger responses such as defense and sex in many animals.

-- From News Services

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