Tuesday, September 13, 2011

Its just Evolution, not a big deal…




I have been a bit lax on the blog posts lately due to some fall travel and trying to get lab work done before teaching gets too crazy. Speaking of teaching, that is what inspired the subject of today’s post. I will be heavier on the education (less on the musing) today because the biology majors students in our Evolution class seem to have more misconceptions on the basics of evolution than we expected. This prompted me to try to do my part to try and teach some of the non-sciencey people who read this blog a bit about evolution, maybe enough to pass on to someone else or decipher some of the spinning that happens in the popular media.

First, some basic definitions. Evolution is a change in gene frequencies in a population over time. This does not need to occur due to natural selection, it can happen by many different mechanisms. Natural selection as a mechanism for evolution describes that if individuals vary in heritable traits, and if those traits are associated with different probabilities of success in survival and reproduction (i.e. fitness), there will be a shift in the gene frequencies in the next generation to have more of the genes associated with higher fitness.

Natural selection happens to individuals and Evolution happens to populations.
-          Individuals vary and those with poor fitness are selected against (i.e. if you aren’t good at surviving and reproducing you don’t get your genes represented in the next generation).
-          Evolution describes changes in gene frequencies or proportions, so you need to consider more than one individual in order to measure or calculate this change.

Unlike in Pok√©mon, one individual does not evolve into something else during its lifetime. However, like in X-men, genetic mutations within a population can cause certain individuals to be different, and if there is an advantage to the mutation (say, if being able to control someone’s mind increased your fitness, something Prof. X could have taken advantage of) that mutation would increase in frequency and cause an evolutionary change.

Some things evolution is not:
…directed
·         The process of evolution does not predict the future, i.e. it cannot predict that next year will be particularly dry and have individual plants produce more drought-tolerant offspring. Certain organisms may have more variable genes than others or could be more susceptible to mutation, but these traits may simply allow for rapid adaptation to changing environmental conditions.

…for the good of the species                                
·         Evolutionary changes in a population or species are not always positive or going towards an optimal state that makes a species perfectly suited for its environment. Natural selection does act on individuals that are less-suitable or fit in the current environment, selecting against them, resulting in individuals that are more capable of surviving and reproducing in an environment producing more/better offspring. But, this does not mean there is some guiding force making these changes. There are also negative or neutral processes (genetic drift, bottlenecks, inbreeding depression) that also result in evolution that may not have any positive effects on a population or species. 

It is sometimes hard to think that all the vast diversity of life that we have on earth today, and that has existed in the past, came about by the simple process of some individuals making more or better babies than others in response to the conditions they find themselves in. But there has been a long time for this to happen (we think life emerged somewhere around 3.8 billion years ago) and life or death consequences for what traits an individual has. The power of artificial selection (selection of desired traits by humans) can be seen in creating modern corn from the grass teocinte, broccoli, cauliflower, kale, and almost every other vegetable you’ll see at the grocery store from one primitive cultivar (wild cabbage), and dogs of every shape and size (still all the same species), simply from breeding individuals with desired traits over many generations, exemplifies the amount of genetic variation that can be present in one species or population. Now, think of this same process but the species being selected on are confronted with almost infinite combinations of environmental conditions, competing species, available resources, and random mutations. I think it becomes less crazy to think of evolution leading to all of life on earth once you put it in this kind of perspective.

Modern corn/maize on the left, the primitive cultivar teocinte on the right. A bit different, right?


The thing that is maybe the most important is that variation is a constant in biological systems. Unlike physics, where there are laws that if they are wrong we wouldn’t have things like planets, matter, and the universe, biological processes are fundamentally based in the fact that variation at the individual, population, community and ecosystem level is always present or possible. For me, this makes me think that there is always something totally new around the corner as well sets up a framework for making all kinds of predictions about biological processes.

I hope this has given a good primer to the basic ideas of evolution. I have a couple more things that I think are interesting on the basic subject of how evolution works and why it is important, but I will touch on that in the next post.