A lot of old true-to-seed breeds of plants with diverse sets of attributes (like e.g. being more resistant to certain environmental conditions) haven't been cultivated for economic reasons and consequently have become extinct by now.
There are some enthusiasts trying to preserve those old breeds by running seed-banks but they have a hard time to do so even here in Europe because of corporations like Monsanto and their heavy lobbying trying to outlaw this movement.
Arche Noah:
"In the past 100 years we have lost about 75 percent of agricultural diversity worldwide."
https://translate.google.com/translate?sl=auto&tl=en&js=y&pr...
Related - I was just posting on this topic on the Red Delicious thread which popped up on the HN frontpage:
https://news.ycombinator.com/item?id=8301185
Edit: I can't see why this gets downvoted, it is clearly on-topic and relevant.