what's the evolutionary cause of bone structure variation between individuals ?

I'm not a biologist but i've always wondered about the stunning difference of bone structure between individuals .

some have big frames taller with wide shoulders and thick robust bones like this example :

https://imgur.com/dz9M9qg

while some have small frames shorter with narrow shoulders and very thin small fragile bones like this example :

https://imgur.com/uJ3rweE

my questions are :

1/ what is the evolutionary explanation of this if there is or what's your hypothesis?

2/ what the evolutionary reason why some individuals have short and some have long limbs ?

3/ evolutionary reason why some individuals are builds for strength( fast twitch muscle fibers dominant ) while others for endurance ( slow twitch muscle dominant ) ?

my opinion :

those who have their hunter gatherers ancestors hunting large game like Mammoth which provides for them an execessive amount of calories and nutrients and hunting methods that requires strength ( spear throwing ) over generations they developed large strong bodies while some hunters preyed on small animals and were very scarce using methods that didn't require strenght ended up with small frames.

i appreciate any effort .