Fitness Landscape - in Biology

In Biology

Fitness landscapes are often conceived of as ranges of mountains. There exist local peaks (points from which all paths are downhill, i.e. to lower fitness) and valleys (regions from which most paths lead uphill). A fitness landscape with many local peaks surrounded by deep valleys is called rugged. If all genotypes have the same replication rate, on the other hand, a fitness landscape is said to be flat. The shapes of fitness landscapes are also closely related to epistasis, as demonstrated by Stuart Kauffman's NK-Landscape model.

An evolving population typically climbs uphill in the fitness landscape, by a series of small genetic changes, until a local optimum is reached (Fig. 1). There it remains, unless a rare mutation opens a path to a new, higher fitness peak. Note, however, that at high mutation rates this picture is somewhat simplistic. A population may not be able to climb a very sharp peak if the mutation rate is too high, or it may drift away from a peak it had already found; consequently, reducing the fitness of the system. The process of drifting away from a peak is often referred to as Muller's ratchet.

In general, the higher the connectivity the more rugged the system becomes. Thus, a simply connected system only has one peak and if part of the system is changed then there will be little, if any, effect on any other part of the system. A high connectivity implies that the variables or sub-systems interact far more and the system may have to settle for a level of ‘fitness’ lower than it might be able to attain. The system would then have to change its approach to overcoming whatever problems that confront it, thus, changing the ‘terrain’ and enabling it to continue.