Evolutionary Biology Blogι**=7/3ψ
by Lars Witting

Mass selects intra-specific interference

The competitive interaction fix-points of the selection attractors on mass, given 2D interactions for the evolutionary steady state. The attractors are defined by the intra-specific resource bias (ψι), and this makes the level of interference (ι) a function of the average cost gradient (ψ) per unit interference.

With interactive competition selecting net energy into interactive quality, we need to predict the level of interference in order to predict the course of evolution. And for this we need to understand the natural selection on mass.

We have already seen that the natural selection of mass plays a central role in evolution, in the sense that body mass allometries are explained by the ecological geometry of the density dependent interactive competition that selects net energy into body mass (Witting, 1995).

Yet, the natural selection of mass may play an even more central role by its ability to determine the level of interference competition in the population (Witting, 1997, 2003, 2008). The quality-quantity trade-off, where a parent may produce many small or a few large offspring, makes the population density and interference competition a declining function of mass. And this makes the level of interference competition a direct function of the selected net energy and body mass in the population.

It follows from this that it is the selection attractor on mass that will determine the level of interference competition in the population. The attractor is generally mass invariant; yet it is dependent on the selection status of the average net energy and on possible selection constraints on mass. The result is a set of attractors for the selection of mass; with each attractor having its own level of interference that selects for a unique type of organism.


  • Witting, L. 1995. The body mass allometries as evolutionarily determined by the foraging of mobile organisms. Journal of Theoretical Biology 177:129--137.
  • Witting, L. 1997. A general theory of evolution. By means of selection by density dependent competitive interactions. Peregrine Publisher, Århus, 330 pp, URL http://mrLife.org.
  • Witting, L. 2003. Major life-history transitions by deterministic directional natural selection. Journal of Theoretical Biology 225:389--406.
  • Witting, L. 2008. Inevitable evolution: back to The Origin and beyond the 20th Century paradigm of contingent evolution by historical natural selection. Biological Reviews 83:259--294.