Ram studies may explain sexuality in humans

CORVALLIS, Ore. – Researchers at Oregon State University think that new studies showing that about 8 percent of rams are “male-oriented” have the potential to help explain sexuality in other mammals, including humans.

The findings, by researchers at Oregon State, Oregon Health and Science University and the U.S. Department of Agriculture’s Sheep Experiment Station, suggest that homosexuality may be biologically driven, a hot topic in the perennial “nature vs. nurture” debate.

“We’re after a basic biological understanding of how the brain works, and the neurons that drive sexual behavior,” said Fred Stormshak, distinguished professor of animal science at Oregon State, and an investigator on the project.

The study began in 1995, when researchers at the federal Sheep Experiment Station in Dubois, Idaho, noticed that some rams refused to mate with female sheep. Of these animals, some showed no interest in males or females, and a fraction preferred to mount other rams. A refusal to breed can spell disaster in the sheep production industry, where high-quality rams can cost up to $500.

Stormshak said a key goal is to find a biological test to determine ovine sexual orientation, so that breeders can make informed purchases of stud rams.

Oregon State gets its homosexual rams from Dubois. The rams are raised and studied on campus, and their brain tissue and blood samples are analyzed at OHSU. In 2001, the project received a three-year grant for about $800,000 from the National Institutes of Health. Charles Roselli, OHSU professor of physiology and pharmacology, partnered with the national sheep center to determine what causes homosexuality in sheep. He and his team renewed the grant in 2004 for another five years and about $2 million.

The researchers found marked differences in the brain anatomy and hormones between male- and female-oriented rams, Stormshak said.

In rams who like other rams, the anterior preoptic area of the hypothalamus was about half the size of this part of the brain in heterosexual rams, he said.

“This was exciting to us because this area of the brain has been found in many species to regulate sexual behavior,” Stormshak told The Gazette-Times of Corvallis.

The investigation also targeted aromatase activity in the hypothalamus. Aromatase is an enzyme that converts androgens such as testosterone into estrogens such as estradiol. In male mammals, estrogen causes masculinization of the brain during gestation.

According to Roselli, the team hypothesized that low levels of aromatase in the brain of the developing fetus somehow keep it from becoming fully masculinized.