Why are some plants, in nature I assume, not due to human intervention, self polinating? Wouldn’t this lead to a lack of diversity in the plants gene pool? Or is it just there as a risk protection if there aren’t any other similar plants to date in the area?
It might seem strange but the whole point of self-pollination is usually to reduce genetic diversity.
The ‘logic’ behind the system is that any plant that has survived long enough to set seed is already sufficiently adapted to survive wihtin that environment, by definition. Since that is the case it is actually a major risk for the plant to go and interfere with that winning system by diluting its genes with the genes from outsiders that may be growing in completely different environemnts. After all a beemay have carried the pollen from a plant gowing many miles away on a different soil type, different moisture regime, different light regime etc.
To overcome that to some degree plants become self-pollinating. That way their offspring always inherit the same genes, though not in the same combinations. That should mean that, on average, the seeds produced will have a better chance of survival in the same environment. Of course the downside is that if the environment changes or if the seeds are carried to a new location they may have a severely reduced ability to survive.
Perhaps the most extreme utilistaion of the system is to be found amongst the violets. Violets produce two distinct types of flowers. The cross pollinated flowers are large and showy and found on long stalks. The seeds they produced tend to be scatterd widely because they develop on stalks. But violets also produce self-pollinated flowers that never open that are borne directly form the stem. The seeds they produce always fall close to the parent plant. The basic idea being that if the seeds can be kept in the same environment as the parent self-pollination is a way to replicate a proven formula with minimal risk.