The purpose of reproduction is to give birth to progeny to continue the species. The marriage is social contract adopted by human beings during its social evolution to maintain law and order within the society and protect culture.
Genetic disorders are very common in consanguineous (people from same ancestors) marriages and results from pooling of genetic defects within a small community. As eugenics, to overcome this during the social evolution, our Ancestors had proposed to promote marriages in community amongst people with different germ lines coming from non-consanguineous families so as to dilute the genetic defects.
To achieve this, any one of the partners has to leave its family and adopt the other family with different Germ line.
Since females are physically, mentally and emotionally stronger than males and it would be easier for them to adopt new family with entirely different beliefs, culture and atmosphere, the ritual that wife has to adopt new family began.
So, few rituals are definitely scientific and were proposed to promote Eugenics.