Genome heterogeneity drives the evolution of species

Most of the DNA that composes a complex organism is noncoding and defined as junk. Even the coding part is composed of genes that affect the phenotype differently. Therefore a random mutation has an effect on the specimen fitness that strongly depends on the DNA region where it occurs. Understanding how this heterogeneous composition influences the fitness evolution of individuals is hampered by the complexity of the problem and a clear picture is missing. Here we study a minimal model for the evolution of an ecosystem where two antagonist species struggle for survival on a lattice. Each specimen has a unique toy genome that codes for its phenotype. The gene pool of populations changes in time due to the effect of random mutations on genes (entropic force) and of interactions with the environment and between individuals (natural selection). We prove that the relevance of each gene in the manifestation of the phenotype is a key feature for evolution. In the presence of a uniform gene relevance, a mutational meltdown is observed. Natural selection acts to quench the ecosystem in a nonequilibrium state that slowly drifts, decreasing the fitness and leading to the extinction of the species. Conversely, if a specimen is provided with a heterogeneous gene relevance, natural selection wins against entropic forces and the species evolves, increasing its fitness. We finally show that heterogeneity together with spatial correlations are responsible for spontaneous sympatric speciation.