There is a large gap between survival and having a well-balanced diet for 13+ developmentally critical years. As strange as these sounds, the US actually has problems in this area resulting in a noticeably shorter population. There where likely successful tribes in the short term 45,000 years ago where people actually grew to 6 feet in height, but the average case is likely worse.
One thing to consider is population growth was fairly slow overall. Just 5% every 100 years and 2 people grow to ~6.8 billion in 45,000 years and there where far more than 2 people back then.
One thing to consider is population growth was fairly slow overall. Just 5% every 100 years and 2 people grow to ~6.8 billion in 45,000 years and there where far more than 2 people back then.