The caste system amongst Hindus in Kerala can not be categorised strictly with what is popularly known as the fourfold division of Brahmin, Kshatriya, Vaisya, and Sudra. Nambudiris formed the Brahmins of Kerala and Varmas also known as Raja and Moopil Nairs formed the Samanthan Nairs (Samanta Kshatriyas) or the ruling class. As per some historians selected Nairs were offered the Samanta Kshatriya status by Nambudiris. There was a strange mixing of various caste equations that Vivekananda called Kerala a lunatic asylum. It is believed that caste system as per Aryan norms began to be categorised after the arrival of Nambudiris into Kerala. In addition to various castes, Kerala had a tribal population residing mostly in hilly areas who did not integrate into the new formed caste systems. Nairs formed the second largest Hindu caste and most of them were very influential feudal aristocratic landlords. Nairs formed the martial backbone of Kerala. Nambudiris, Samanta Kshatriyas, Nairs (Including Samanthan Nairs), Ambalavasis were considered to have had a more privileged life in pre-independence Kerala. Therefore the benefit of caste based reservations was not extended to them. In addition there were also caste who generally served in temples known as Ambalavasis or Pushpaka Brahmins, who were considered lower to Namboothiris. There were other castes in Kerala who were considered further below Ezhavas, these are Kuravas, Arayans, Pulayas and Paraiyars.
In post independence Kerala, castes may be classifieds as General category, Other backward castes, scheduled castes and finally scheduled tribes.
This category includes castes such as Nambudiris, Samanta Kshatriyas, Nairs, Ambalavasis and Syrian Christians. They are not extended reservations in government jobs and educational institution due to their relatively better economic and educational status in pre-independence Kerala. However amongst these castes, Nairs have become most influential due to their numerical superiority. Unlike in North India, the proportion of Brahmins(1.4%) in Kerala is not very significant. Hindu Forward Castes form around 16% of the population of Kerala, while Syrians form another 9.5%. Therefore, the Forward Castes makes up around one fourth of the population of Kerala.
The decrease in the Forward caste population has been extremely steep in Kerala, compared to other parts of India. During the 1816, 1836 and 1854 censuses, the forward castes outnumbered the other Hindus by a huge margin. Despite the conversion of large number of Outcaste Hindus to Christianity, Caste Hindus became a minority during 1860s and 70s and during the 1931 and 1941 censuses, the Outcaste Hindus numbered almost twice as much as the Caste Hindus. For example, Nairs numbered two times as much as the Ezhavas during the 1854 census (30% to 15%). But as of 1968, Ezhavas outnumbered Nairs significantly (22% against 14.4%). The reasons might be the high death rates among the Malayala Kshatriyas due to frequent warfare and Kudippaka as well as the low birth rate among the Malayala Brahmins.
Ezhava, Muslim Mappilas (Christian Mappilas are forward caste), Latin Christians, Arayan,Izhuvan, Ezhutachan, Kalasi Panicker, Kalari Kurup or Kalari Panicker, Kaniyar Panicker, Kusavan , Viswakarmas, Veluthedans and Vilakkithalavan have been classified as a backward caste by Kerala government due to the discrimination faced by them historically.
Paravan, Cheruman, Mannan, Nayadi, Pallan, Thotti, Vetan, Vettuvan, Panan etc. are some of the castes who have been included in the scheduled caste list of Kerala. These castes were generally in the bottom of caste hierarchy and faced worst kind of discrimination. Scheduled Castes, along with Scheduled Tribes form 10.95% of the total population according to the 2001 census. es
As per historians untouchability started in Kerala with the advent of Nambudiris. In Kerala, anyone who was not a Namboothiri, was treated by the Namboothiris as an untouchable. The Namboothiris had different rules regarding the degrees of pollution for the different classes. If a Namboothiri happens to touch or comes in physical contact with an Embraanthiri, he gets the Embraan Sudham, which is supposed to be one step lower in rank among various types of purity of Namboothiris. But it is not compulsory that an adult male Namboothiri should bathe before performing "sandhyaavandanam" if he is polluted due to "Embraan sudham". Also Namboothiris will get Eda Sudham if they are polluted by the touch of Iyers. Namboothiri women (and not men) are not permitted to eat if they become Eda Sudham. For doing Sandhyaavandanam, Namboothiris should take bath if they are polluted with Eda Sudham. Asudhams are practised not only by Namboothiris, but also people of other communities in Kerala, such as the royal families, temple employees, Nairs, etc., who are closely associated with Namboothiris. Other South Indian Brahmanans also follow this custom. Clothes of Namboothiris, washed by Veluthedans , if touched by other Nairs, are not impure. But if touched by a person below the rank in the hierarchies of caste system, it becomes impure. Other classes had different distances after which they could be considered polluting. For example, if an Ezhava got within 24 feet of a Namboothiri, the Namboothiri was considered to be polluted. Untouchability was not isolated to Hindus in Kerala, amongst Christians the original Syrian Malabar Nasranis considered newly converted Latin Christians (usually fishermen) to be untouchables.
The most extreme form of untouchability in all of India was practised in Kerala.
A Nair was expected to instantly cut down a Mucua,thiyya who presumed to defile him by touching his person; and a similar fate awaited a slave, who did not turn out of the road as a Nair passed" According to Kerala tradition the Dalits were forced to maintain a distance of 64 feet from Savarnas as they were thought to pollute them. Other castes like Nayadis, Kanisans and Mukkuvans were forbidden within 72 feet, 32 feet and 24 feet respectively from Savarnas.
When British banned the right of the Nairs to carry swords with them, caste related violence steeply decreased. The observance of untouchability vanished consequent to the movements of social reforms, especially the one initiated by Sree Narayana Guru. Temple Entry Proclamation of the Raja of Travancore effective by put a end to the system of untouchability in South Kerala.
The present day Keralam before that period was a part of "Thamizakam" and the language was "Chenthamiz", during "Sankakalam" and later Cheras, Cholas and Pandyas were the three prominent rulers of "Thamizakam". "Muziris" was the most important city of "Cherakkam". Uzavar, Panner, Parayar, Parathar (fishermen), Kurumber were the main communities of that time, and the Cheras were the ruling class and they worshiped Kottave a tribal deity and they were inimical to Aryan system of north India. They worshiped the spirits of their ancestors along with 'Kottave'. The majority people were Uzavas (farmers) and Paravans (fishermen) who followed Buddha dharma (Buddhism)came through Eelam (Sri Lanka). A later majority of Uzavas stayed as Ezhavas/Thiyyas (people from Ezham, "deep") and a significant portion of Paravans became Christans and Muslims. Jainism came through Mysore and Karnataka, and there were a number of Jains in Kerala. Muziris, Maduri, Panthalayanikollam, Vizinjam and such cities and costal areas had Roman, Jewish, Arab, Chinese settlements, thus the Semitic religions came to India, and there were also a few Aryans (Brahmins & Nairs) also settled in these cities but at that time they were neither influential nor had any significant presence in society.
Then came 100 years of war between the Cheras and the Cholas, and at first the Cheras lost heavily and Chera power started to vanish, and this time with the help of Nairs, the Cheras formed "Chavers" (suicide squads) and finally were the Cholas defeated. During this time the social system started to change, with Brahmins elevating their position in society. The Cheras lost many men in the battlefield and Chera women started to have Brahmin partners, the matriarchal system started, these Brahmins received local customs and imposed their vedic and knowledge and became Namputhiris, their children's and relatives from the Cheras became Nairs, and Adi Sankara established Brahmin supremacy among other ideologies especially among Buddha dharma (Buddhism), and the Namputhries (Namboothiris) accepted and integrated so many local beliefs and rituals such as Chera king of ancient time "Well kezu kettavan" myth became the Parasurama myth etc. The story of Brahmins converts to Christianity came much later stage, one thing that is sure is that during AD 1 st centuries itself there were Christians in Kerala, St. Thomas converts and some Jews who settled before them and the locals (Uzavas, Paravas etc.) an probably some converts from Buddhist and Jain priests. In history you can see that people from lower castes have a tradition to imitate the upper castes, such as the Ezhava/Thiyya adoption of matrilinearism and Naga worship in Malabar from the Nairs.
Mannappedi or Pulappedi was a custom which existed until 17th century. An upper caste woman could lose her caste if any male from the castes like Pulayan, Parayan or Mannan happened to see her or touch her by any means. Then she would be expelled from the caste or had to move with the "low caste" person or will be under discretion of the elders to decide. This would apply especially on the night of a specific day that fell in the month of Karkatakam (roughly corresponding to the dates 15 July to 15 August) in the Gregorian calendar . Given the social and economic status of lower caste people of that era, it is believed that this practice could not be perpetuated without social sanction, and definitely not without the connivance and/or tacit support of the men of upper castes. Thus, the men folk used this in the garb of a custom to stifle the freedom or rights of women belonging to upper castes such as the Nairs . Another view of the practice is that it was a route provided by tradition to the oppressed Pulayan class for registering their intentions of revenge as a symbolic act . The practice was abolished by the then Kerala Varma in 1696  after which he had to face the ire of the royal servants (Pandarathu Kuruppus) . Prepared by Royson J Pazhamannil
In old Kerala society the castes were classified as Brahmins, Kshatriyas and Avarnas. Non-Hindus were also considered Avarnas. Many native rulers, most of whom were Nairs, were crowned as Samanta Kshatriyas, with the help of Tulu Brahmins who migrated or were invited to Kerala during medieval times.
The caste system had its legitimacy in the positive responses to many of its institutions by the non-Brahmins.
The opposition to caste system took various forms. While some castes refused the position of their community or refused to accept higher position of other community. In other cases, many individuals completely disagreed with caste divisions.
The most abused castes (now known as scheduled castes) showed their opposition to the system by creating and worshipping new spirits for the persons who suffered due to caste atrocities in north Malabar.
Artisans (known as Kammalan / Vishwakarma / Vishwabrahmin in Kerala), in all south India, paradoxically, fought for a higher position in the caste system. According to John Fryer, who vistited India in 1670, the members of Kammalan caste held themselves equal to Brahmins and disputed the higher position of Brahmins. The weavers and goldsmiths in Karnataka, Tamil Nadu and Andhra Pradesh created their own priest systems.