Natural selection is a driving force in evolution and can generate populations that are adapted to survive and successfully reproduce in their specific environments.  However, this means that natural selection cannot produce an organism that is perfect.  It cannot create anything from scratch so this puts a limit on the populations genetic variance.  We are limited from historical constraints, it must adapt existing structures to new situations.  Natural selection is also limited because it acts on the phenotypes of individuals, not alleles.  A phenotype is the set of observable characteristics of an individual resulting from the interaction of its genotype with the environment.

What would a perfect organism look like?

In whole this question is unanswerable, although everyone has their own definition of ‘perfect’.  Natural selection creates organisms that are suited to their own environment, susceptible to the constraints of history, and the mechanisms of mutations. Meaning that a perfect organism is impossible to happen with these constraints.

We might ask ourselves, “why doesn’t everyone have 20/20 vision?” Natural selection only selects traits that improve fitness in our current environment.  As someone who needs glasses, I don’t understand why we all don’t have 20/20 vision then, as it is not something that would decrease fitness.  So we have to take in account the constraints.

I made this Punnett Square to display the probability of myself requiring glasses.

Our first constraint is the history in our DNA.  For example, both my mother and father require glasses, making the probability of myself needing glasses quite high. These genes have been inherited for generations, and will continue to be.  Although eyesight can also be be influenced by the environment.  You may be born with ‘perfect’ eyesight but environmental factors such as the conditions of where you are reading and aging may cause you too develop the requirement for glasses later on in life.

The next constraint is mutation.  Mutations are changes to an organisms DNA.  Species are able to evolve because of the accumulation of mutations over time.  A mutation won’t exactly affect how well you see but colour blindness in the eyes is caused by a gene mutation. Our eyes have three cones, and these cones each contain a specific pigment. The mutation occurs when one of these cones is disabled. This is much more common in males since the colours red and green are only found on the X chromosome.

Overall this taught me that organisms cannot be created to meet all expectations and be ‘perfect’.  Also that evolution has no purpose, since it isn’t used to turn a population into a predetermined ideal. There is no expectations.  Any organism can carry some beneficial alleles and some unfavourable alleles.  While natural selection selects the fittest individuals and often results in a more fit population, other parts of evolution including genetic drift and gene flow, often do the opposite by introducing deleterious alleles to the population’s gene pool.  All of this makes the chances of a perfect organism happening impossible.