Derivatives are securities. So what's a derivative? Let's say you have a house. It's worth X. Let's say I decide to sell stock in the value of your house. It's worth X x Y, with Y being whatever the fuck I want it to be. The underlying fundamental value of your house and the stock combined is X. However, the securities value of your house is X plus X x Y. It's not as completely simple as that (you can't trade your house on the stock market... at least, if you're living in it) but options, futures contracts, derivatives, mortgage-backed securities, they're all securities. "Fixed income securities" are basically bonds, issued by bond issuers, backed by whatever the fuck they feel like backing it with. It's all just contracts.
So we reached a worldwide doubling in fixed income securities (in 6 years) because wealth and fund managers went hog wild with derivatives and other financial instruments? I forget who said it, but they said the last good financial instrument invented was the ATM. I know that's cheeky and simplistic, but derivatives seem to me to invite speculation. edit: I think it was Paul Volcker.
"Anyone who believes exponential growth can go on forever in a finite world is either a madman or an economist." - Ken Boulding, 1973