Below is the list of tables from the database along with their columns and datatype. Need to generate an accurate SQL query for the question.
Only use the columns present in the respective table. Only use the columns which are required to generate the SQL query. Only use table joins if required and not otherwise.

### Tables ###
TABLE: CREATE TABLE table_71507 ( "Member countries" text, "Population" text, "Area (km\u00b2)" text, "GDP (billion US$)" text, "GDP per capita (US$)" text )

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

### Accurate SQL ###

SELECT "Population" FROM table_71507 WHERE "Member countries" = 'existing members (1973)'