杂种 has two sharply different uses. In biology it means 'hybrid' or 'crossbreed' and is neutral in scientific contexts. As a slang insult, it is a highly offensive swear word equivalent to 'bastard' or 'son of a bitch' in English. Never use it to refer to people of mixed ethnicity (混血儿 is the appropriate term). The insult usage is extremely vulgar and can provoke strong anger.