Evolutionary tradeoff

An evolutionary tradeoff is a situation in which evolution cannot advance one part of a biological system without distressing another part of it. In biology, and more specifically in evolutionary biology, tradeoffs refer to the process through which a trait increases in fitness at the expense of decreased fitness in another trait. A much agreed on theory on what causes evolutionary tradeoffs is that due to resources limitations (e.g. energy, habitat/space, time) the simultaneous optimization of two traits cannot be achieved. Another commonly accepted cause of evolutionary tradeoffs is that the characteristics of increasing the fitness in one trait negatively affects the fitness of another trait. This negative relationship is found in traits that are antagonistically pleiotropic (one gene responsible for multiple traits that are not all beneficial to the organism) or when linkage disequilibrium is present (non-random association of alleles at different loci during the gametic phase). The general concept behind evolutionary tradeoffs is that in order to increase fitness (or function) in one trait it must come at the expense of the decrease in fitness/function of another trait. The ‘Y-model’ states that, within an individual, any two traits are determined by resources from a common pool. Although a useful tool that has provided valuable insight, the ‘Y-model’ has been oversimplified in much of the literature. Researchers have made different mathematical expansions to the ‘Y model’ in order to gain insights about evolutionary tradeoffs. An important point that many authors make when discussing the concept of how tradeoffs affect evolutionary change is the ambiguous use of the word ‘constraint’. The term ‘constraint’ has two meanings: hindering (slowing), but not stopping evolution in particular directions, or that there are certain evolutionary trajectories that are not available to selection. The distinction between the two senses of the word is important because according to the first definition all character states, or forms, are possible, where as according to the later definition some character states are unattainable.