Simplify the following text for a Grade 7 native English-speaking person.
Original: Homosexual and bisexual behavior are widespread in the animal kingdom : a 1999 review by researcher Bruce Bagemihl shows that homosexual behavior has been observed in close to 1500 species , ranging from primates to gut worms , and is well documented for 500 of them .
Simplified: Bruce Bagemihl did research in 1999 . It shows that homosexual behavior has been observed in close to 1500 species , from primates to gut worms , and is well documented for 500 of them .