This paper describes the opportunity of natural selection in relation to age at marriage and household income among the Kom tribe of Churachandpur District in Manipur. A total number of 235 of mothers aged 40 years and above were included in the sample for computing the indices of the opportunity for natural selection according to Crow’s formula and its modified version by Johnston and Kensinger. It is found that the total index of opportunity for natural selection is low when compared with other populations. The index of opportunity for natural selection due to differential fertility was greater than that due to differential mortality. It was also found that the total index of opportunity for natural selection was negatively associated with age at marriage and income level of the households. It is suggested that the operation of natural selection in contemporary populations is declining due to cultural development such as changes in socioeconomic conditions and technology, particularly in the fields of medical sciences.