The question of how same-sex marriages are responsible for population dynamics in India requires a nuanced discussion, as their direct impact on population growth (birth rates) is generally considered negligible or indirect, unlike heterosexual marriages which are traditionally linked to procreation.

Direct Impact (on Birth Rates): From a purely biological and demographic perspective, same-sex marriages do not directly contribute to population growth through biological reproduction within the marital union. The primary demographic indicator, the Total Fertility Rate (TFR), is driven by heterosexual couples. Therefore, an increase in same-sex marriages would not, by itself, lead to an increase in birth rates. If anything, a hypothetical scenario where a significant portion of the population enters same-sex unions instead of heterosexual unions could, in theory, lead to a decrease in the overall birth rate, assuming no alternative reproductive methods are used.

Indirect Impacts and Broader Demographic Considerations: However, the discussion can extend to broader demographic and social implications:

1. Adoption and Surrogacy: While same-sex couples do not biologically reproduce together, they can contribute to population dynamics through adoption or assisted reproductive technologies (ART) like surrogacy. If same-sex couples are legally allowed to adopt children or use surrogacy, they would be contributing to the existing population (through adoption) or to new births (through surrogacy). In India, the legal landscape for same-sex couples regarding adoption and surrogacy is still evolving and complex. If these avenues become more accessible, it could have a minor, albeit positive, impact on the number of children being raised within families.
2. Social Recognition and Well-being: The legalization and social acceptance of same-sex marriages can lead to improved mental health and well-being for LGBTQ+ individuals. A more inclusive society might reduce social stigma, discrimination, and associated health issues, potentially leading to a healthier and more productive population overall. While not directly affecting birth rates, a healthier population contributes positively to demographic quality.
3. Resource Allocation and Social Planning: As same-sex marriages gain recognition, there might be implications for social planning, resource allocation, and policy-making related to family benefits, healthcare, and social security. Demographers and policymakers would need to consider these new family structures in their projections and planning, even if the direct impact on population size is minimal.
4. Changing Family Structures: The recognition of same-sex marriages signifies a broader shift in the understanding of family and kinship. It expands the definition of a 'family unit' beyond the traditional heterosexual, procreative model. This change in family structure is a significant social dynamic, even if it doesn't directly alter population numbers through births.

In conclusion, while same-sex marriages do not directly contribute to population growth through biological reproduction, their responsibility for population dynamics in India lies more in their potential indirect impacts through adoption/surrogacy, their contribution to social well-being, and their role in reshaping the understanding of family structures and social planning. Their direct demographic impact on birth rates is minimal, but their sociological and policy implications are noteworthy.