Differences between Nāgavanshi Nairs and Ezhavas

Many people have a confusion on whether a southern Indian caste, with martial origin, is related to Nair. On Wikipedia, in an article about Ezhava, I read a sentence as follows, "It has been suggested that the Ezhavas may share a common heritage with the Nair caste." It is also written that numerous customs have been adopted by both the castes but they have not mentioned which customs. There is a common belief about Ezhavas that their ancestors were migrants from northern part of Sri Lanka which is also called Ezham. The prominent language in the northern part of Sri Lanka is Tamil and the dialect spoken there is called Ezham Tamil. The birth name of Sreenarayana Guru was Nanu. Nanu is also a Tamil name which means shy or modest. 
The caste system of the Sri Lankan Tamils resembles the system of Sinhalese, but individual Tamil castes differ from Sinhalese castes. The dominant Tamil castes, constituting well over 50 percent of the population, are the Vellala. Then are Karaiya, who traditional occupation was fishing, Chetti, a group of merchant castes and the rest are artisan castes and laboring castes including the Palla. Sri Lankan Tamils are also called "Ezhathu Tamizhar (ஈழத் தமிழர்)". 

Sub-divisions of Ezhava community

According to Census Report of 1901, the four Illams of Ezhava community are Muttillam, Madampi or Pallichal, Mayanatti and Chozhi.
The sub-divisions of Ezhava community are as follows, Kollakar or Channar Ezhava, Malayalam Ezhava, Pandi Ezhava, Nadi Ezhava, Pachili Ezhava, Puzhuckar Ezhava. The Channar Ezhava are mainly engaged coconut cultivation and agriculture. Malayalam Ezhava cliam they belong to Kerala from the very beginning. The Pandi Ezhava are said to have migrated from Tamil Nadu. The Nadi Ezhava are those who mainly engaged in palm toddy tapping. The Puzhuckar Ezhava were the menial servants of Malayalam Ezhava. Pachili Ezhava are those who were married to the fishermen. Of all these divisions, the Channar or Kollakar Ezhava claim a higher status while Pachili and Puzhuckar Ezhava are at the bottom of the hierarchy. 
There are no such sub-divisions and Illams in Nair community. In Nair community, The Naduvazhi chiefs, by whatever designation they were styled, whether Raja or Achan or Kaimal or merely Nair, belonged to one of the three classes, viz., Swaroopi, Prabhu and Madambi. That is, among Naduvāzhis, Madampi was the name of  classes and not titles. 

Religious art forms

Aivarkali, Mayilppili Tukkam, Makachuttu, Poorakkali, Theyyam and Villadichaampattu are the religious art forms of Ezhava community. None of them are practiced and performed by Nairs. Pallichans and Maniyanis, are Theyyam worshippers, and they have their own shrines for their Theyyams. 

Marriage and dowry

I don't know how were wedding rituals of the Ezhava community before the reformation. When I referred some books I got a few details about it. Among the Ezhavas of Palakkad, the bridegroom in olden times never accompanied the marriage party. In Ezhava marriages the bridegroom's sister would take the "Pudava" (dress), accompanied by the marriage party, to the bride. After the reformation, the practice and bride and bridegroom sitting face to face and getting married after exchanging garlands replaced the old custom of marriage by proxy among Ezhavas. 
None of the customs were and are followed in Nair community. On the wedding day, the Pudava is given directly by the groom to the bride. Even today, in the weddings of Nair community the ritual of giving Pudava is followed as it is. 
Dowry seems to be very important in Ezhava community. In Children's Lifeworlds: Gender, Welfare, and Labour in the Developing World by Olga Nieuwenhuys it is stated that, "An Ezhava girl, for instance, have the option of either saving for a dowry from her (nominal) wages or meeting educational expenses if she is sufficiently bright in studies. The ideal of self-reliance has its impact on the amount of dowry an Ezhava girl is expected to bring, that tends to be comparatively low. Most of it is raised by the bride herself and with the help of the credit revolving among neighbours and relatives." Usually the dowry is paid at the engagement ceremony, but some pay it on the wedding day. 
In Nair community, dowry is not important and most of the families do not ask dowry from the bride's family. Women are not forced to get a job and earn money for the dowry. 

Divorce 

An account of the customary practice of divorce among the Ezhavas in ancient times revealed that if either party wanted a divorce, relatives and village elders were informed. If a compromise was not effected, the husband had to pay the wife 'Azhivu' (a "compensation for damage to the youthfulness and health of the woman"), 'Chelavu' (cost of marriage) and 'Ozhivu Pudava' (the 'release' cloth which the husband presented to his wife to mark the end of the relationship). Another form of divorce was that effected through mutual consent, through the "wish of the husband supported by the decisions of the caste assembly" and wife receiving a share of her husband's property or 101 fanams or a deed for 101 fanams by the husband.
After the reformation, divorce was permitted to both the genders in Ezhava/Thiyya community. It can be by mutual consent or on any reasonable grounds at the will of any of the partners. If it is the interest of a single partner, then the elderly members of the community in the locality after hearing the appellant and respond, give their verdict. Accordingly, the compensation and other matters are fixed. Among the patrilineal group the responsibility of children lies on father and among the matrilineal group lies on the mother after the divorce. However, nowadays, it is mainly dealt by the SNDP Yogam leaders and sometimes by the court of law. Widow/widower and divorcee(male/female) are permitted to remarry. Sororate and levirate are not a custom a, but also are not objected. 
In Nair community, from ancient times, both men and women were allowed to terminate their marriage if they had problems with it. The women were not able to terminate the union except with their Karanavan's and kinsmen's consent. After the Nair act of 1925 was passed, the divorces began to be settled in court. Paying of the Azhivu, Chelavu and Ozhivu Pudava was not there in Nair community. Sororate and levirate are considered shameful in Nair community. 

Gender determination

In Poinson Damsels by Penzer it is stated about Ezhava community that, "Among the ceremonies is that which determines the gender of the unborn child. The priestess pours a quantity of oil on the navel of the woman from a betel leaf, and, from the manner in which it flows down, the gender is determined." There is no such ritual in Nair community. 

From the above details it is clear that Nair community and Ezhava community are not related to each other. I don't know about the martial connection of Ezhava community. But there are many martial communities in India and all of them have different ancestries. The Bunt community of Tulu Nadu was once said to be related to the Nair community. But most of its rituals are different from the rituals of Nair community. For example, the serpent worshipping of Nair community is entirely different from the serpent worshipping of the Bunt commnuity. Chekavar or Chovvan is another martial community of Kerala but that too is not related to Nair community. 



Reference: Sri Lanka: Current Issues and Historical Background by Walter Nubin, The Sacred in Popular Hinduism: An Empirical Study in Chirakkal, North Malabar by A. M. Abraham Ayrookuzhiel,  Kerala: yesterday, today and tomorrow. National Book Agency by E. M. S. Namboodiripad, Global Encyclopaedia of the South Indian Dalit's Ethnography, Volume 1 edited by Nagendra Kr Singh, Applied anthropology and challenges of development in India by P. R. G. Mathur, Slow Flows the Pampa: Socio-economic Changes in a Kuttanad Village in Kerala by K. E. Verghese, Politics, Women and Well-Being: How Kerala became 'a Model' by Robin Jeffrey.