In Islam it is said that human being came from the Adam and Eve and it is added that when they get married, they had 41 children and they were twins. Holding this into hand, does Islam permit marriage between siblings?
The Permanent Committee for Scholarly Research and Ifta' said regarding the issue:
Regarding the fact that Adam (peace be upon him) married his sons to his daughters, this is something that he did according to the law that Allah commanded him to follow which we do not have any right to argue about. Anyway, as far as the Shari`ah (Islamic law) that was sent to Prophet Muhammad (peace be upon him) is concerned; Allah makes it Haram (prohibited) for a man to marry his sister along with other well-established categories of women that a man is not allowed to marry. Besides, since Allah (Glorified and Exalted be He) says,
To each among you, We have prescribed a law and a clear way [Surah Al-Ma'idah 5:48]
While mentioning the laws of Tawrah (Torah), Injil (Gospel), and Qur'an; the same applies to Adam (peace be upon him) i.e. he had a specific law that he followed.
For us, is the Shariah that was revealed to Muhammad (salallahu alayhi wassalam) and we follow that. And this Shariah clearly forbids marrying between siblings. There are many things that were not legislated before and legislated now for example 5 daily salat. The wisdom behind all this is known only to Allah as he is most Just and the Lawgiver.
Source: Adam and Eve
When asked a similar question, Imam Ja‘far as-Sadiq (a.s) replied that Adam (a.s) married 2 of his sons (Shith and Yaafith) to 2 huries (Nazala and Mauzela).
Also according to Imam al-Baqir (a.s), Allah also married a female jinni to another of Adam(a.s)'s son. Therefore beauty in creation due to the huri and ugliness due the Jinn. The Imam emphatically denied that Adam married sons to daughters.
First of all Islam does not support Marriage between Siblings. They are clearly forbidden in Quran Surah Al-Nisah 4:23
Prohibited to you [for marriage] are your mothers, your daughters, your sisters, your father's sisters, your mother's sisters, your brother's daughters, your sister's daughters, your [milk] mothers who nursed you, your sisters through nursing, your wives' mothers, and your step-daughters under your guardianship [born] of your wives unto whom you have gone in. But if you have not gone in unto them, there is no sin upon you. And [also prohibited are] the wives of your sons who are from your [own] loins, and that you take [in marriage] two sisters simultaneously, except for what has already occurred. Indeed, Allah is ever Forgiving and Merciful.
But yes there is a question, how generation can be propagated when all children of Adam and Even were brother and sisters. Isn't that forbidden in Islam? The answer is Islamic laws did not apply to full extent at that time. Just like Zakat was not imposed until later years in Islam, there was no sin on not paying it. Also Alcohol were allowed in Islam initially (here allow means not specifically banned), then they were banned. So if you drank before, there was no sin on you. So if something happened before Almighty awarded his decree on the subject, it was allowed and totally acceptable.
My Own Take
From scientific point of view. This is a very weak and over simplification of how human race started. Most likely this is not true. For this to be true, the entire evolution theory must be wrong and Adam and Eve must have existed only 5,000 years ago. Furthermore we have to allow Incest to make this model work, which is clearly forbidden by all religion and laws out there. I must mention there is nowhere in Quran and Hadith (that I am aware of) says incest were allowed for Adam children. These are merely our theories. Islam or any other religion essentially is lacking on this subject.
When the Quran used the word "Adam," it's not used as a singular name rather it's a plural. According to the Arabic rules of language, there are distinct forms for a plurality of two and a plurality of three or more, and the word "Adam" uses the plural of three or more, which means at least three groups of humans were created.
So marriage between siblings was not a concern, as children from each of these three groups could intermarry without being siblings to each other.