Exactly a year ago, I came across this image in the July 2011 issue of National Geographic:
It's a comparison of the varieties of seeds available a century ago versus those found in the National Seed Laboratory in 1983. The change eighty years had is shocking and I think after read the article I told people about it for days. 288 of beets! Now we have seventeen. The diagram shows 554 varieties of cabbage. Now a mere twenty eight are left. Charles Seibert writes in the article that "In the United States an estimated 90 percent of our historic fruit and vegetable varieties have vanished."
One of the first things I did at the farm was start seeds with Devin. On a rainy day, we went into the house, sat on the floor and he showed me his collection of seed packets; so many kinds of melons, of tomatoes, of greens. Now, as we're harvesting them, I'm learning some of their names. The other day we harvested a type of garlic called "music." There are tomatoes called "pineapple" and "noir." When we shop solely at the grocery store I don't think we get the whole picture. For all the choices we have there and the bounty we seem to have access to, we've lost the diversity our ancestors took for granted just a few decades ago.
The importance of having a diversity of plant varieties isn't all about aesthetics (as in a honey colored variegated tomato v. a plain red one) or even taste. Certain varieties developed and were bred so they would be adapted to a specific environment; the local environment. But in an attempt to produce the greatest yields, farmers began and now continue to favor plants that are meant to adapt to many kinds of environments. These plants are genetically engineered and biologically less stable than the heirloom varieties.
And it isn't just seeds. There are heritage breeds of livestock; chickens, cattle, sheep, pigs.
Though the biodiversity side of this issue is widely important, I feel the cultural impact is critical as well. An extinct breed or variety is a cultural artifact that has been lost. The result is generalization. Societies shift and change, true, but we need to remember that the story of people cannot be separated from the story of the land.
I highly recommend reading the article from National Geographic. And also this post from RAFI-USA.
For heirloom seeds, I suggest taking a look at Baker Creek.