I just finished the book Extra Life: The Astonishing Story of How We Doubled Our Lifespan by Steven Johnson.
Human life expectancy more than doubled over the past century:
It wasn't doctors.
One thing we have done is helped more infants live through adolescence. This brings up the average of our life expectency. Additionally, he gives several other reasons.
3 factors account for saving the lives of billions:
5 factors account for saving the lives of hundreds of millions:
Those that have saved millions are those we attribute to doctors such as:
These 21 factors account for the bulk of why we are living so much longer per this author ... and I think he's right.