Hybrids, on the other hand, are a result of cross-breeding two parents of different genetic makeup.  Unlike open-pollinated plants, the seeds from hybrids will not come true from seed but will be highly variable and thus not desirable.  Hybrids were originally developed for their high productivity, uniformity and wide adaptability.  In addition, these hybrid vegetables ripen in a shorter period of time and they often have a tougher skin that allows them to be shipped great distances and stored for long periods with what is known as "shelf life."

As a matter of fact, hybrids were developed to counteract some of the qualities of heirlooms such as the latter's tender skin (which allows for easier bruising), shorter shelf life and less-than-perfect form and shape.  But there's one key "ingredient," if you will, of heirlooms that modern hybrids have yet to approach and that is flavor.  Heirlooms simply taste much better than the newer, "man-made" varieties can hope to.  When hybrids were originally bio-engineered, the beefing up of certain characteristics, such as tougher skins and longer storage life, meant a corresponding decrease in other traits, namely flavor.  This is why today's supermarket tomatoes have the consistency and, many would say the corresponding taste of a tennis ball.