The overall sex ratio (number of females per 1,000 males) in any population is influenced by three main factors:
Sex Ratio at Birth (SRB)
Definition: The ratio of male to female babies at the time of birth.
Natural Tendency: Slightly favors males due to biological reasons.
- Typically, around 105 male babies are born for every 100 female babies (SRB ≈ 950 females per 1,000 males).
Biological Basis:
- Determined at fertilization (X or Y chromosome from the father).
- Influenced by fetal mortality (male fetuses are more biologically fragile).
In India: The SRB is often lower than normal (fewer females) due to sex-selective abortions driven by societal preference for sons.
Sex Ratio of Deceased Persons
Male Mortality: Higher male mortality rates at all life stages — from infancy to old age — due to:
- Biological vulnerability of male fetuses and infants.
- Riskier lifestyles, occupations, and behaviors in males.
Female Advantage: Women generally have higher life expectancy, contributing to a more balanced or even female-favoring sex ratio at older age groups.
Sex Ratio of Net Migrants
Migration Patterns: Migration is often gender-selective, particularly in developing countries like India.
- Males migrate more frequently for employment, especially to urban areas.
- This leads to a male-dominated sex ratio in cities.
Impact on Overall Ratio:
- While migration doesn’t drastically alter the national sex ratio, it significantly skews the urban-rural gender balance.
Summary Table
| Factor | Effect on Sex Ratio |
|---|---|
| Sex Ratio at Birth | Slight male bias (natural), worsened by sex-selective practices |
| Sex Ratio of Deaths | Higher male mortality improves sex ratio over time |
| Net Migration | Male-dominated migration reduces female ratio in urban areas |
