In addition to the difficulties of putting the BSC into practice, a second problem is that it overlooks some organisms. For example, because it is based on the sexual exchange of genetic information, the BSC cannot apply to species that reproduce asexually, such as bacteria. Although some asexual species do occasionally exchange genetic information in a process known as conjugation (Chapter 26), true asexual organisms do not fit the BSC.

Furthermore, because it depends on reproduction, the BSC obviously cannot be applied to species that have become extinct and are known only through the fossil record, like different “species” of trilobites and dinosaurs.

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