What is isolation? Describe the major isolating mechanisms which lead to speciation. (UPSC 2021, 20 Marks, )

अलगाव क्या है? उन प्रमुख अलगाव तंत्रों का वर्णन करें जो प्रजातिकरण की ओर ले जाते हैं। (What is isolation? Describe the major isolating mechanisms which lead to speciation.)