Homosexual behaviour in animals :  an evolutionary perspective / 
edited by Volker Sommer, Paul L. Vasey. 
 - Cambridge ;  New York :  Cambridge University Press,  2010 
 - IX, 382 p. :  ill. ;  26 cm. 
<br/><br/><label>ISBN: </label>9780521182300 (pbk) 9780521864466 (hbk)