"Hindu Samskaras" by Rajbali Pandey bcoz he traces the origin of some customs in it. He says early smrithis did not prohibit swagothra weddings. Only the later ones did.
This book "The position of women in hindu civilization" by Anant Sadashiv Altekar is also interesting. He mentions in pages 73-74 about the prohibition of swagothra marriages being unknown even in the puranas. It first apepared in grihasutras and was enforced by later smrithis.
In a very very specific case Mahaperiava, in one place, has said that if ' ghunam' ' khulam' are ok, nothing else should come in the way for proceeding with the alliance.
I feel the statement of " sagothra marrige is not permitted' must have originated when that practice was existing. Is it not?. Do you prohibt something that is not existing?
In a court case Delhi sessions court has said Hindu marriage act foes not prohibit sagotara marriage.
I feel if there is not relation exists in the previous six generations between the two families then same gotra marriage is not a taboo.
I read a very interesting write up on this
People from all castes have gotras. The sages were by definition - and without exception - all brahmins. By that logic, no other caste ought to have a gotra. There is an explicit bypass to the gotra rule. In same gotra marriage cases the bypass allows for the bride to be ceremonially adopted (a token gesture) by the groom's maternal family, which is by definition of a different gotra than that of the groom's family. By doing so, her gotra changes to the one on the groom's maternal side and she can then marry the boy - and of course, by default again revert to her original gotra - the same as that of the groom. If this really was a clan endogamy taboo, such deliberate bypasses would not exist.
So then, what is after all a gotra? The word actually comes from gay attire. The word "gau" means a cow - or cows. In the Vedic times, disciples of a rishi would pay tribute to the master by giving cow(s) to him - a valuable resource in the pastoral and agrarian community of those times. So all those who gave cows to the same rishi were classified as notional brothers. It has no linkage at all to clan, kinship or actually family blood ties. A notional brother may be treated similarly to a real one under prevailing social ethos, but remains quite different from the POV of marriage alliances ties.
In any case, it is quite impossible to establish at this point in time as to which individuals of a gotra may originally have had shared kindhip ties in those distant times and which did not. Given the venerable ancestry of the custom and the sheer number of generations that have passed since then, the distinction is also entirely academic in present times. Ergo, the gotra taboo is no more than a mindless and meaningless custom that simply carries on in ignorance.
A peculiar custom of south India a girl marrying her mother's brother (mama) is more dangerous than marrying some one whose gotra is same as mine but having no blood relations in the immediate known past.
यो मां पश्यती सर्वत्र सर्वं च: मयि पश्यती
तस्याहम न
प्रणश्यामी स च मे न
प्रणश्यति
"He who sees me everywhere, and sees everything in Me, he
never gets separated from Me, nor do I get separated from him" -Bhagwat Gita
Ch. VI verse 30