If the MRCA(Eve) was only in regards to all living females and MRCA(Adam) was only in regards to all living males then it makes sense that way. But if all living humans are descended from MRCA(Adam) then we also must all be descended from his mother. It must be so. This is not a push for male primacy on my part. Adam is getting first billing because he is said to have 75,000 years ago while Eve is said to have lived 150,000 years ago. The same thing would be true in reverse if the numbers were switched.