Okay, here's the deal - let me lay it out there for you. When a boy reaches a certain age, a new brand of hormones begins to rush through every cell in his body, causing odd (often embarrassing) behaviors. The boy's entire anatomy is prepping him for procreation - the continuation of the species.... and so his instincts kick in, completely overriding any semblance of good sense. He is looking for one thing - the opposite gender, preferably naked (assuming he's heterosexual).
Unfortunately, we no longer are members of the Clan of the Cave Bear, and so must exercise some degree of restraint and abide by the laws of society. For many boys, the first glimpse of the opposite sex in their mad hormone driven hunt is their dad's stash of nudie magazines. If that doesn't pan out, there's always plans B and C: the National Geographic or Sears Catalog.
This sort of illicit reading material provided a sort of research for the young lads. Before they went out and got their hands dirty, they needed to be familiar with the material.
It sounds ridiculous (and exceptionally lame) to women, but this has often been the first step to manhood for the past fifty or so years. Guys that tell you their first experience seeing a female in her birthday suit was with the babysitter are liars.
Well, that era is gone. I don't know if they even make Sears Catalogs anymore, or even National Geographic. And, nowadays, if a kid got hold of dad's pornos, it would probably traumatize him for life - let's just say things have gotten more explicit. I assume this awkward stage is traveled via the internet these days, and the ol' JC Penny lingerie section looks pretty damn stupid in comparison.
Well, stupid or not, here's some scanned pages from ye olde catalogs. Enjoy!
Sears Fall-Winter 1972
Sears Catalog Fall-Winter 1970

