Question Summary:
Marriage between cousins

Question Detail:

I want to ask you a very important question.It is about cousin marriages which are so common among Muslims.I want to know where this practice stems from,where it originated.I got a bit confused and i don't know whom to believe.If you allow me i will explain to you why
I sent a question with the same content that is cousin marriages to two Islamic sites.The first of them didn't answer and the second one gave a very detailed answer yet their answer contradicts the results of the scientific research on this problem.Their medical consultant who was reluctant to introduce himself wrote that genetic counseling is not necessary when couples whose parents are cousins are planning a child or when couples who are cousins themselves.He wrote that there was almost no health risk which is why cousin marriages are not harmful..
As such an answer didn't put an end to my doubts i soon visited the official site of the Arab Centre for Genomic Studies because i am the kind of person who always searches the truth and i have got the right to know it.I read there that scientific results confirmed the connection of many genetic disorders with the practice of cousin marriages.I also found there that unlike popular belief Islam doesn't encourage or advocate such marriages and the sermons of the Prophet Muhammad Hadith state that close marriages will often produce weak children.
Now i do not know what to believe.So I think that initially the Prophet didn't forbid such practice the tribes were isolated from other tribes which created certain difficulties in marrying people of other nationalities or just distant people not relatives.I tend to believe Arab Centre for Genomic Studies more .
Am i right ? i think not forbidding cousin marriages is one thing and encouraging it is a completely different thing. If science proves the negative consequences of inbreeding then logically it must be discouraged and people have the right to know. So what is the real stance of Islam on this problem?

Answer :

In the Name of Allah, the Most Gracious, the Most Merciful.
As-salāmu ‘alaykumwa-rahmatullāhiwa-barakātuh.
We commend you on your enthusiasm to search for the truth. Searching for the truth is definitely your right, and it is encouraged in Islam. May Allah Ta'ala continue to guide you to search for the truth, increase your knowledge, and give you the ability to act upon it. Ameen.  
At the outset, it is important to understand that Shari'ah merely permits marriages between first cousins. Such marriages are categorized as mubah (permissible).They are neither prohibited nor emphasised in Islam.  
The permissibility of such marriages is deduced from the general verse:
وَأُحِلَّ لَكُمْ مَا وَرَاءَ ذَلِكُمْ..الاية
Translation: (After discussing the relations with whom marriage is prohibited)Allah says: And lawful for you are [all others] besides these.
The Holy Prophet (sallallahu alaihi wa sallam) himself married his first cousin Zaynab bint Jahsh (radhiyallahu 'anha) who was the daughter of his paternal aunt.[1] The Holy Prophet's (sallallahu alaihi wa sallam) daughter Fatima (radhiyallahu 'anha) was married to Hadhrat Ali(radhiyallahu 'anhu) who was the first cousin of The Holy Prophet(sallallahu alaihi wa sallam) . 
 
 
The "Hadith" which you have referred to is as follows[2]: 
"لَا تنْكِحُوا الْقَرَابَة الْقَرِيبَة فَإِن الْوَلَد يخلق ضاويا"              
Translation:
"Do not marry close relatives, for verily your child will be born weak."
The famous renowned Muhadith Hafiz Ibn Salah (rahimahullah) comments regarding this hadith[3]:
قال ابن الصلاح: لم أجد له أصلًا معتمدًا                  
 Translation:
"I could not find any authentic chain for this Hadith."
Hafiz Al Iraqi (rahimahullah) further comments[4]:
وقال الحافظ زين الدين العراقي: والحديث المذكور إنما يعرف من قول    عمر أنه قال لآل السائب قد أضويتم فانكحوا في الغرائب.        
 
 
 
Translation:
"The abovementioned Hadith is actually a saying of Hadhrat Umar (radhiyallahu 'anhu). He (radhiyallahu 'anhu) said to the people of Saib, "Verily you have become weak, start marrying outside of your clan." [5]
One should also keep in mind that Hadhrat Umars (radhiyallahu 'anhu)  statement was as a mushwara (opinion) and not as a command.
Hafiz Zanjani (rahimahullah) comments[6]:
قال الزنجاني: ولأن من مقاصد النكاح اشتباك القبائل لأجل التعاضد واجتماع الكلمة وهو مفقود في نكاح القريبة.
 
 
 
Translation:
"From the benefits of nikkah (marriage) is joining the different clans, for mutual assistance, and to join under one rule. All these are lost in close marriages."
 
You have stated: "If science proves the negative consequences of inbreeding then logically it must be discouraged and people have the right to know"
Being born with a deficiency, disability, deformation etc. is not confined to close family marriages. Not all deformed children in the world are offspring's of parents who were close family members. There are other factors for deformity besides close family marriages.
Accordingly, the scientific research on this is not conclusive. We have consulted appropriate persons in the medical field and hereunder are their responses:
”There are different genes in the DNA, some dominant and some recessive. Some genetic diseases are caused by dominant genes and some by recessive. In the case of a dominant gene, any person having that gene will have the disease. You get one set of genes from each parent. In case of recessive genes, if only one parent is giving you the abnormal gene and you get a normal gene from the other parent, you will not have the disease even though you are carrying a defective gene and can still pass is on to your kids if your spouse also is a carrier (one normal and one abnormal) or if she/he has the disease (both abnormal genes).
 
The issue with cousin marriages is that the gene pool is usually limited. If a tribe has only been marrying their own for some generations, it's the same genes going around. If someone is carrying a disease there are more chances that more family members will have the disease since everyone is marrying in the same gene pool. Some tribes/families will intermarry but since they have no genetic diseases, they don't get any unless there is a mutation somewhere and is passed along to the next generations."
 
"I don't know the religious aspects of this , but as far as medicine goes, yes, intermarrying for generation after generation usually results in more genetic diseases or similar traits to manifest. For example a family/tribe/clan that have blue eyes and only marry their own will all have blue eyes until someone marries someone with only genes for brown eyes. You can trace other physical features as well.” 
 
"The problem arises when there is intermarriages for some generations with no external genes coming in. Hope this answers your question. The medical community is still in infancy when it comes to genetic research”
-Dr. Sohaib Khalid, MD, U.S.A
 
"Scientific information in this regard is confusing and at times contradicting. At best one can say that 'there is slight possibility of increased likelihood of certain birth defects in off-spring of couples in close relation to each other'. 

It's an issue that has been politicized beyond its merit amongst other issues like abortion, contraception, homosexuality, etc. Most of us tend to use religion and science as it conveniently fits our perspective. One has to be cautious in taking a strong stance in either direction. I think there is no absolute right or wrong in here. We have to take it case by case and avoid generalization."
-Dr. Junaid Ghadai, MD, U.S.A
It is clear from the above that marriages with close family members is permissible. If one were to consider the scientific aspect and not marry with a close member, then that is his choice, Shari'ah does not restrict him from that either. However, bear in mind that if close marriages were conclusively harmful, Shari'ah would not have permitted such marriages.     
And Allah Ta’āla Knows Best.
Abdullah Ghadai
Student Darul Iftaa
Michigan, U.S.A 
Checked and Approved by,
Mufti Ebrahim Desai.