What's a Baby Shower for?

On Saturday I attended a baby shower for a family friend (actually the son of my parents' friends...he and his brother used to teach me and my sister tennis when we were kids. And now he's having a baby! Good lord!). This was my first baby shower (the only thing close was the small bridal shower brunch I went to for my college drawmate), and I think it set the bar pretty high for the rest of my baby shower attending career. 

We had wonderful food (with fresh fish! smoked and grilled!) and cake from Diamond Bakery. Everyone was friendly and felt like family, and we all played silly games...and we had lots of presents, which made it feel like Christmas for the happy couple.

But may I ask: What's a baby shower for? Or a bridal shower? There must be a historical significance that has been lost over the years, and now it seems a little bit like a consumerist gift-giving occasion. (This one on Saturday wasn't really, but still.) What confuses me even more is a bachelorette/bachelor party. If you have to have a hyper sexualized weekend in order to prepare yourself for your ball and chain, why get married at all? Confused...

[I need to brush up on my gift wrapping skills...]