Frozen Evolution. Or, that’s not the way it is, Mr. Darwin. A Farewell to Selfish Gene.

The ability of organisms to adaptively respond to environmental changes (evolvability) is usually considered to be an important advantage in interspecific competition. It has been suggested, however, that evolvability could be a double-edged sword that could present a serious handicap in fluctuating environments. The authors of this counterintuitive idea have published only verbal models to support their claims. Here we present the results of individual-based stochastic modelling of competition between two asexual species differing only by their evolvability. They show that, in changeable environments, less evolvable species could outperform their more evolvable competitors in a broad area of a parameter space, regardless of whether the conditions fluctuated periodically or aperiodically. Highly evolvable species prospered better nearly all the time; however, they sustained a higher probability of extinction during rare events of the rapid transient change of conditions. Our results offer an explanation of why sexually reproducing species, with their reduced capacity to respond adaptively to local or temporal environmental changes, prevail in most eukaryotic taxa in nearly all biotopes on the surface of Earth. These species may suffer several important disadvantages in direct competitive battles with asexual species; however, they might win in changeable environments in the more important sorting-according to-stability war

Ecological theories of sexual reproduction assume that sexuality is advantageous in
certain conditions, for example, in biotically or abiotically more heterogeneous environments.
Such theories thus could be tested by comparative studies. However, the
published results of these studies are rather unconvincing. Here, we present the results
of a new comparative study based exclusively on the ancient asexual clades. The
association with biotically or abiotically homogeneous environments in these asexual
clades was compared with the same association in their sister, or closely related, sexual
clades. Using the conservative definition of ancient asexuals (i.e., age >1 million
years), we found eight pairs of taxa of sexual and asexual species, six differing in the
heterogeneity of their inhabited environment on the basis of available data. The difference
between the environmental type associated with the sexual and asexual species
was then compared in an exact binomial test. The results showed that the majority of
ancient asexual clades tend to be associated with biotically, abiotically, or both biotically
and abiotically more homogeneous environments than their sexual controls. In
the exploratory part of the study, we found that the ancient asexuals often have durable
resting stages, enabling life in subjectively homogeneous environments, live in the
absence of intense biotic interactions, and are very often sedentary, inhabiting benthos,
and soil. The consequences of these findings for the ecological theories of sexual
reproduction are discussed.