In India, your fate and future are often sealed at the moment of your birth, depending on your ancestors' place in society.

Key points: India's caste system is the world's oldest surviving form of social stratification

India's caste system is the world's oldest surviving form of social stratification It affects most aspects of people's lives, including how they vote in elections

It affects most aspects of people's lives, including how they vote in elections PM Modi's historic 2014 election win was partly due to his appeal across castes

Despite rapid urbanisation and change, the caste system remains highly relevant in modern India.

And with the world's biggest democratic election set to begin this week on April 11 the issue is back in the spotlight, raising questions as to how the caste system could impact the ballot.

Here's a look at what exactly the caste system is, how it fits into India's democracy, and how it could influence the upcoming elections.

First off — what is the caste system in a nutshell?

The caste system has been legally abolished but is still a significant part of India's culture today. ( ABC News: Jarrod Fankhauser )

India's caste system is the oldest form of surviving social stratification and was formalised around 1,000 BC.

Based on the Hindu teachings of karma (meaning fate based on your previous life) and dharma (meaning duty and order) it later evolved to include followers of other prominent religions in India including Islam and Christianity.

Though discrimination based on caste was legally abolished in 1948, the system still permeates many aspects of a person's life: it can determine where someone lives, works, who they marry, where they pray — and who they are likely to vote for.

The caste system separated Hindus into four main categories based on the different parts of the body of Brahma, the god of creation, with castes ranked from highest to lowest depending on their position from head to toe.

Upper-caste Brahmins, for example, are seen as representing Brahma's head, and are often priests and academics.

On the other end of the scale are Dalits, who are not afforded a position on Brahma's body. Also known as 'untouchables', they're generally considered outcasts and are consigned to the kind of work no one else will do, such as cleaning latrines.

There are now some 25,000 subclasses in India, with the government classifying those who are considered educationally or socially disadvantaged as Other Backward Classes (OBC), and those who are not as Forward Castes.

Can you have a real democracy with the caste system?

Mr Modi's historic victory during the last elections will be hard to replicate due to his waning popularity. ( Reuters: Munish Sharma )

Diego Maiorano, a research fellow from the Institute of South Asian Studies at the National University of Singapore, said the caste system is considered India's "most fundamental social institution".

The ability of the caste system to adapt to wider societal changes has been fundamental in shaping India's brand of democracy, Mr Maiorano told the ABC.

Quotas for Other Backward Class: India allocated government jobs quotas for the lowest castes in 1960, broadening this in 1989

India allocated government jobs quotas for the lowest castes in 1960, broadening this in 1989 To reverse discrimination OBCs are now entitled to 27 per cent of public sector positions

To reverse discrimination OBCs are now entitled to 27 per cent of public sector positions But the latest Right to Information data shows they only hold 12 per cent of those roles

But the latest Right to Information data shows they only hold 12 per cent of those roles Most allocated posts remain unfilled, raising questions about the system's effectiveness

As a former British colony, India's democracy is based on the Westminster system, but also takes on a number of its own characteristics rooted in Indian tradition, particularly the dominant religion of Hinduism.

This includes complex personal laws, which are applied differently to individual religions.

There is also a system of affirmative action that reserves a quota of higher education places, public sector jobs, and legislative seats for lower castes.

While quotas have improved representation in Parliament, the very existence of the quota system serves to highlight caste identities and asserts these hierarchies within both the Lok Sabha and Rajya Sabha, the lower and upper houses respectively.

Dalits are traditionally seen in India as being in the bottom of social order and subjected to jobs such as "manual scavenging". ( Wikimedia Commons: Dalit Network )

Assa Doron, professor of anthropology and South Asia at the Australian National University, told the ABC that caste has become a political "identity marker".

"India's caste-based calculations are part of an ongoing dynamic democratic process, just like other countries where interest groups influence political outcomes," he said.

Dr Doron added that "segregation and socio-economic deprivation" is also a crucial aspect that is "validated" by the caste system, which "is often at odds with the framework of liberal democracy".

But while Mr Maiorano said "prejudices are hard to die", conditions at the bottom of the social order have improved over time.

How might it affect India's upcoming elections?

The Dalit community make up about 15 per cent of India's population. ( Flickr: UN Women Asia Pacific )

Dalits make up about 15 per cent — or 200 million — of India's 1.3 billion people, dwarfing the number of upper-case Brahmins, who comprise about 5 per cent of the population.

All parties have, at least rhetorically, tried to woo this large bloc of lower-caste voters, according to Mr Maiorano.

"It's often said in India, you don't cast your vote, you vote your caste," he said.

And historically there have been many instances where political parties mobilised groups across caste fault lines, including the 2007 triumph of the Dalit-backed Bahujan Samaj Party in elections held in the most-populous state of Uttar Pradesh.

"In the current run-up to the elections we see similar patterns, with various parties trying to solicit the support of caste groups and associations by fielding candidates from those castes," Dr Doron said.

Prime Minister Narendra Modi — a former tea salesman and so-called OBC — won the 2014 election in large part due to his ability to appeal to both the Bharatiya Janata Party's (BJP) established upper-caste voter base and lower-caste voters who identified with his personal background.

However, caste-based politics is far more complex for political parties than simply encouraging voters to back a politician in the same caste as them, as attempts to appeal to lower-caste voters can lose them higher-caste voters, and vice versa.

Analysts warn Mr Modi’s historic victory will be difficult to replicate due to his waning popularity — particularly among rural workers — as well as eruptions of caste-based violence and a series of broken election promises.

Mr Modi has been accused of playing caste politics by his main opposition. ( AP: Rajesh Kumar Singh )

His main rival in the upcoming elections is Indian National Congress party leader Rahul Gandhi, a Brahmin descended from India's most powerful political lineage, the Nehru-Gandhi family, who claims that Mr Modi has been segmenting Indians based on their caste.

However, while all political parties have a stronger following among certain castes, Mr Maiorano said "a political party does not win the elections on the basis of caste".

Other key issues going into the election include the record levels of unemployment in India and national security amid tensions with neighbouring Pakistan.

"But [a party] cannot win without the right set of caste equations either," Mr Maiorano said.