Both. I started doing this because my area was populated after industrial farming started. Local adaptation slowed drastically after it was possible to ship food such long distances. Prior to that every food grower kept seed and brought them to new environments. I came to realize that all my seed comes from at least 8 degrees closer to the equator than me that are generally warmer, have a longer summer and are certainly dryer.
Starting with a new plant I will buy a few varieties whose descriptions suit my fancy. Then plant as many seeds as I have space for. Adapting plants is a numbers game. Some won't germinate, some will grow slowly, some will become diseased and some will be eaten by pests. None of those are suited for the local environment. Thin the planting to allow the strongest growers room. It should be obvious which ones to keep. Once you have the plants that started from seed best its time to start selecting for other traits. Traits depend on the plant but for food you should be selecting mostly for taste at first. For example, I am crossing one pea variety selected for wirey strong vines and purple pods and a couple others for taste. This is my third year with those and I am getting sweeter pods on wirey vines but the vines aren't quite as strong or tall. So, I planted some of the original wirey vine seeds to try pushing the line that way more.
Some trait selection is unintentional. The plants are going to adapt to you as well. They will adapt to how you plant, harvest, and save the seed. With my grains some of the plants are too short to harvest with a sickle comfortably. Those go in the eat or feed to chickens pile. Some also don't separate from the plants when I thresh by hand. Also to the chickens. What I am left with are seeds that were easier to process just by not being super careful to get everything. With biennials or clonal root crops you will also unintentionally select for plants that store well as you have to keep the roots over winter to plant them in the spring.
I started saving seed about 5 years ago so nothing has really stabilized into something that could be considered a new variety. But, I have seen the steps closer to my goals.
Purchased seeds are a narrow part of that plants gene pool. If they are open pollinated they were bred until most of the produced seeds make the same looking and tasting plant in a specific environment. Really, if you are gardening, you should learn how to save seeds unless you have a seed grower near you. If you save seeds you will also have more seed than you know what to do with.
Starting with a new plant I will buy a few varieties whose descriptions suit my fancy. Then plant as many seeds as I have space for. Adapting plants is a numbers game. Some won't germinate, some will grow slowly, some will become diseased and some will be eaten by pests. None of those are suited for the local environment. Thin the planting to allow the strongest growers room. It should be obvious which ones to keep. Once you have the plants that started from seed best its time to start selecting for other traits. Traits depend on the plant but for food you should be selecting mostly for taste at first. For example, I am crossing one pea variety selected for wirey strong vines and purple pods and a couple others for taste. This is my third year with those and I am getting sweeter pods on wirey vines but the vines aren't quite as strong or tall. So, I planted some of the original wirey vine seeds to try pushing the line that way more.
Some trait selection is unintentional. The plants are going to adapt to you as well. They will adapt to how you plant, harvest, and save the seed. With my grains some of the plants are too short to harvest with a sickle comfortably. Those go in the eat or feed to chickens pile. Some also don't separate from the plants when I thresh by hand. Also to the chickens. What I am left with are seeds that were easier to process just by not being super careful to get everything. With biennials or clonal root crops you will also unintentionally select for plants that store well as you have to keep the roots over winter to plant them in the spring.
I started saving seed about 5 years ago so nothing has really stabilized into something that could be considered a new variety. But, I have seen the steps closer to my goals.
Purchased seeds are a narrow part of that plants gene pool. If they are open pollinated they were bred until most of the produced seeds make the same looking and tasting plant in a specific environment. Really, if you are gardening, you should learn how to save seeds unless you have a seed grower near you. If you save seeds you will also have more seed than you know what to do with.