Answer:
(Fatwa: 48/48=M/1429)
Intermarriage is lawful in Islam i.e. one can marry his (parental or maternal) cousin sisters etc provided there is no other reason of being haram like co-suckling. According to you, as per the science, intermarriage leads to disorder, what you mean by disorder.
Allah (Subhana Wa Ta’ala) knows Best
Darul Ifta,
Darul Uloom Deoband
