Jessica,
TIAA Traditional is the foundation of an excellent portfolio. For example; in today's environment you're getting 5% or 5.75% without any risk! There's no other fund that can offer that. Never mind the common advice that it doesn't protect you against inflation. Yes, it does protect you because it's always compounding. (Einstein was even astounded by compounding!) You certainly don't need Money Market as a retirement investment because that's just a temporary shelter, nor do you actually need bond funds that are riddled with risk, just to earn approximately the equivalent return of TIAA Traditional.
TIAA Real Estate is a one chance of a lifetime to own actual commercial real estate. If you can get that someplace else, please let us know. Just because it is corrupted by owning 2% of its value of REITS volatile crap, doesn't mean that it isn't a great investment. Look at its great 12 year history and also how it's holding up against the current market decline.
That leaves Equities.(What are equities? answer: stocks) (What are funds? answer: stocks.) Nobody really knows what they'll do. But because you have a longer time span to invest, and the past has indicated that long-term, the greatest increase in value to be equities, it's advisable to put a certain percentage into them. (Or should I say an uncertain percentage?) Equities tend to make you the most uncomfortable of all because nobody likes to lose, and that happens often with stocks. So spread your bets by diversifying across the various types of equity funds available to you, cross your fingers and hope for the best.
Sy