Expert: Dana Krempels, Ph.D. - 5/13/2007

Question
Hi,

There is an aspect of evolution that is puzzling me. Am I right in thinking that evolution works by a process of RANDOM mutation and that if a particular feature/mutation of a species happens to be beneficial (by chance) in any given environment, then that species will survive and prosper and so go on to propagate those genes?

Taking that to be my starting point, I do not understand how certain symbiotic relationships arise simply by a process of random mutation. For example, flowers imitating insects to attract them, ants farming aphids and other examples where clearly the species is born with these traits. Now, how can that process be a product of random mutation? The chances of a flower randomly mutating to look like a bee or to excrete insect-attracting pheromones is surely highly improbable, even over these massive time periods.  

Clearly I am misunderstanding something fundamental and would really appreciate clarification.

Many thanks,

Ed  

Answer
Dear Ed,

This is a question that many have discussed and argued ever since Darwin ever put forth his ideas about natural selection.  I think that one reason that people get confused about this is because they have a preconceived notion that evolution is somehow "directed," and that it has a purpose.  It does not.  The current thinking is that accumulated chance traits (sometimes encoded by one gene; sometimes by many, interacting genes) may provide an unexpected evolutionary advantage, meaning that for some reason (and not necessarily the one for which the traits eventually end up being "used"), the trait/s contribute to the organism bearing them leaving more genes to the next generation.

But also note that an organism is a product of *many* genes,  and some traits that are at any given moment either neutral (i.e., not affecting an individual's reproductive fitness) or even maladaptive (i.e., potentially reducing an individual's reproductive fitness) may sort of "come along for the ride" in a changing environment where different traits may or may not be adaptive in any given generation living in a particular environment (with all its selective pressures).

Traits do not always appear incrementally.  There are some mutations (or possibly alternative expressions of existing genes) that can cause *massive* phenotypic change in an individual expressing it.  Examples include things like albinism (one gene mutation), ABo blood types (single change
in the terminal sugar on one of the blood immunoglobins), and even blue/brown eye color (though overall eye color is affected by at least five genes).

An excellent overview of how small mutational changes can result in complex structures can be found here:

http://www.actionbioscience.org/evolution/nhmag.html

I think you'll enjoy it!  :)

Hope this helped a little bit.

Dana