Lecture 16-17 BIO152 The Origin of Species L16 flightless : can?t fly but its a really good swimmer Biological species concept states a species is group whose members have potential to interbreed in nature and produce viable, fertile offspring mule is viable but not fertile reproductive isolation-barriers that prevent two species from breeding reproductive isolation is classified if it happens before or after fertilization sperm of one species may not be able to fertilize the other- gameric isolation they may be viable in one generation but not the others- hybrid breakdown post zygotic barriers have to do with hybrids beluga seal intrasextual- inflates balloon to warn of males if they approach and use his balloon again to attract female (intersextual)