Below is an instruction that describes a task. Write a response that appropriately completes the request.

### Instruction:
What is the Population of the nation that has a Member countries consisting of existing members (1973)?

### Inputs:
table_name: table, columns: ['Member countries', 'Population', 'Area (km²)', 'GDP (billion US$)', 'GDP per capita (US$)']

### Response:
SELECT Population FROM table WHERE Member countries = existing members (1973)