Most of us know that incest is wrong, either through cultural conditioning or what appear to be innate evolutionary cues, yet some humans can’t seem to resist the urge to have sex with their relatives. In fact, since the DNA of every living human is 99.9 percent the same, it may be much more common than we think. Still, that doesn’t mean incest can be acceptable in any case. As we will see, breeding with a close relative can result in some dire consequences.
Most living things benefit from genetic diversity when breeding, including plants, which have developed their own mechanisms to prevent self-pollination. Many plants are hermaphroditic, meaning they have both male and female reproductive organs, which makes it easy to self-pollinate. To prevent this, some plants, such as petunias and tobacco plants, have evolved to develop what scientists have dubbed the “self-incompatibility” strategy.
As a part of this strategy, some plants can identify their own pollen once it has entered the female reproductive organ (called the pistil) and destroy it before fertilization occurs using a toxin called S-RNase. Though the S-RNase is produced even when genetically diverse pollen has entered the pistil, the plant prevents the destruction of viable pollen by withholding the toxin until it has identified the pollen as either compatible or incompatible.