Tangled bank hypothesis of advantage of sexuality
The tangled bank hypothesis, named after Darwin’s colourful description of a complicated ecosystem in his book “The Origin of the Species” (Ghiselin 1974; Bell 1982), emphasizes the fact that, in sufficiently complicated ecosystems, lines and species that reproduce sexually have a greater chance of survival in the long term and, because of their greater variability, have a broader ecological valence – are capable of utilizing broader range of available resources. Mathematical models have shown that, if there are at least certain types of habitats in the environment that have a clear selection advantage for suitably adapted members of a sexually reproducing species or line, sexually reproducing organisms can coexist in the long term with asexual organisms and can even force them out under sufficiently restrictive conditions (Doebeli 1996; Lomnicki 2001). In contrast to the elbow room hypothesis (XIII.3.2.1), the tangled bank hypothesis assumes that the mechanism leading to forcing out asexual species is not based on a competitive advantage of sexual organisms following from reduced competition amongst progeny within a single family, but rather on direct competition for resources amongst families or amongst species. It follows from this, amongst other things, that this mechanism may also be valid for species where siblings are randomly scattered in the population and do not primarily compete together.