Is evolution a necessary, logical consequence of mutations plus natural selection?
In other words, was evolution inevitable once modifiable genetic instructions, DNA, existed?
To answer this question a biologically-realistic computer simulation was developed. The program
has adjustable parameters to determine the essential conditions for evolution to occur.
The Simulation Program
The program was developed in the C++ computer language and optimized for speed. Speed is an essential criteria to track individual genetics for a sizeable population over hundreds of millions of years. Even with speed optimization, some simulations took months to run on fast PC's.
Each individual, when born, obtained a random combination of its parents DNA and also unique mutations. The amount and types of mutations were controlled by parameters. The system analyzed the genetics and calculated a genetic fitness score for each individual. Each individual also received an age fitness score. Individuals in their prime were more fit than very young individuals or older ones. Age fitness continually decreased as individuals matured beyond their prime. An environmental fitness score was also assigned to each individual. That is, individuals born in times with plenty of food and minimal disease grew stronger than those born when food was scarce and disease was common. The total fitness score of each individual was based on all three fitness scores.
Each individual's DNA was considered in two sections: functioning systems and developing systems. Mutations to functioning systems are usually harmful, but for developing systems any mutation might be beneficial. Mutations to developing systems do not harm anything useful and there are billions of combinations that might develop into something useful. In the calculation of the genetic fitness score, mutations to existing systems were considered slightly deleterious with a few being more damaging. On the other hand, mutations to developing systems were never considered harmful, but rather were considered potentially beneficial in developing new systems. The simulation had pre-determined many beneficial sequences. Any genetic mutation moving toward a beneficial sequence provided a positive fitness score. The evolution of a new beneficial trait was complete when an entire beneficial sequence was achieved and spread throughout the population.
Breeding Groups and Migration
The simulation was based in an environment that allowed a large, but limited population. That is, resources were limited, so each year the number of births and deaths must be approximately equal. The environment was divided into breeding groups/villages/herds. Normally all mating occurred between individuals within their own group. This allowed advantageous genetic changes to become established through inline breeding. In addition, every year some individuals migrated to neighboring groups. This allowed advantageous genetics of each group to be shared and combined.
Natural Selection occurred at two levels. First, individuals with low fitness scores were much more likely to die than individuals with high fitness scores. Second, natural selection made a difference in mate selection. While all females of reproductive age had offspring, they were much more likely to mate with males of high fitness scores than low fitness scores. Natural selection continually removed individuals who were less fit and provided additional offspring for males who were more fit.
Many different parameter values were tried until a combination was found where evolution succeeded. However, for evolution to succeed four of the parameters had to be set to completely unrealistic values. If even one of these parameters was set to a realistic value, evolution completely stopped.
Four Crucial Parameters
The Real Power of Natural Selection
The simulation showed that Natural Selection is NOT CAPABLE of evolving new traits. However, Natural Selection provides two essential functions. First, it minimizes the damage mutations cause to existing systems. In the simulation, if Natural Selection was turned off, the entire population began a downward trend in accumulated mutations until none survived. With Natural Selection turned on the accumulated mutations were limited and the population was maintained. The second benefit of Natural Selection is in speciation. This is not developing new traits, but rather selecting individuals with traits that best fit the environment. If individuals with established traits are spread into different environments, Natural Selection can quickly standardize the traits in every environment that are best suited for that environment. This quickly produces many different species.
The simulation showed that Evolution by Natural Selection can never produce new traits. However, Natural Selection does minimize harmful mutations to maintain life. It also can quickly modify existing traits of a species so that each species is best suited for its environment.