Evolution: let's get this straight people!

Being in the science field I've seen some pretty interesting misunderstandings about the theory of evolution.  Some funny and some scrape your eyes out painful.  Although the first painful argument I often hear is about evolution being a "theory", that merely stems from people not understanding scientific processes and scientific theories as they differ from your drunk roommate insisting the entire human race is partially controlled by lizard space beings called the Annunaki (this is a real CONSPIRACY theory, check it out).  However, I will delve into that in a later post.

For now I think I will take you through the basics of evolution, in a way I teach all my little youngens in my vertebrate evolution course.  As with class, feel free to ask questions, I will post answers.

Natural Selection: fundamental mechanism (process) by which evolution occurs.  It is based on the struggle for existence and organisms' competition for space and resources.  This includes migration, mutation, genetic disease, and death.  Natural selection requires 3 basic constructs to occur:

1. Variation: individuals within a population differ from each other in their traits (also referred to as phenotype or characteristics)
2. Inheritance: aforementioned traits need to have a genetic basis.  AKA I can pass my awesomeness down on to my children.  (Please note, traits for this CANNOT be acquired-e.g. picked up by the parent through the course of life-it needs to be in the DNA code.  Therefore if you adhere a horn to a horse and have that horse breed, its foals will not be born or develop horns [again, real study way back in the day, check it out])
3. Fitness: given competition and limited resources, not all individuals will have the maximum capacity to reproduce. The struggle for space, food, and survival will cause a gradient in success for mating and offspring.  Therefore, this inequality means individuals will contribute differently to the next generation (high fitness=higher contribution).

Sexual Selection: secondary mechanism that is based not on actual survival but on a potential mate's perception of your fitness.  E.g. red coloring in bird.  Being red does not make you a faster runner but indicates since you are very brightly colored and alive you're probably good at escaping predators.  This includes mate choice, coloration, size, combat, display, plumage, etc.  In some cases, sexual selection can actually work in the opposite direction of natural selection.  Certainly male peacock tail feathers do not benefit them for survival but the ladies think it's awfully sexy!


Constraint: evolutionary limits.  Evolution IS NOT progress towards a perfect organism.  Evolution is more like an engineer piecing together the best option out of some mismatched hunks.  Bear in mind that evolution (generally) occurs over a very long time, and many of the traits you see weren't developed to survive in THIS moment, they were developed THEN.  As their landscape, competition, and resources change they are constantly changing too.  But you don't get to wipe your slate clean every time, you have to use what you've got.  Pigs don't have wings, not because wings wouldn't be beneficial to a pig but because the pig's body design would certainly not support flight.

Teleology: explanations of a trait based on its PERCEIVED purpose rather than natural (mechanistic) origins.  Many non evolutionists fall into this trap, as have some scientists (everybody makes mistakes, it's what you do with them that matters, see later Science post for more on this).

Contingency: chance historic events.  These are things like catastrophes (lightning, eruptions, etc) or continental drift that may strongly impact the evolutionary path but is not based on fitness.  Sort of being in the wrong place at the wrong time kind of idea.



NOW, given the information above the way origins are traced and mapped is called PHYLOGENY.  Historically (aka before we started DNA sequencing everything) this was based on trait relationships, which in some cases were perceived since whether or not traits are similar because of function, common ancestry or common pressures is hard to tell.  You end up with two groups, or two and a half?

1. Homology: traits are similar because they are of common origin
2. Homoplasy: traits LOOK similar because two separate groups underwent similar natural selection pressures (like hopping mice in the African and American deserts-they're not related but they're traits are almost identical since there are only so many ways to deal with movement across sand!).
3. Reversals: this isn't so much a third group as much as a related issue.  Sometimes traits REVERSE or switch back to a previous evolutionary state due to a shift in selection pressures.  As you can imagine, this can really mess up how we try to order things. 

Many of these issues are starting to get worked out with DNA sequencing, where you can see and follow exact mutations and deletions in the code and follow them through time.  

Misunderstood information:

1. Missing link: there is no such thing and it wouldn't be necessary for there to be one.  Changes through evolutionary time are GRADUAL, you can tell because even today with our existing species there is an incredible amount of debate on what is a species and what is a subpopulation.  Certainly it is not any easier when you don't have the ancestor population with you as you make the comparison.  Not only is this process gradual, with small changes occurring and building up over time, but when it doesn't work the individual doesn't reproduce or they die quickly, such individuals are in low enough proportion that they don't contribute to the gene pool or the fossil record.
2. Species that are ill adapted to their system: sure, again GRADUAL.  Evolution takes time so often there is a little bit of a time lag between successful evolutionary adaptation and the landscape they are adapting too.

  

Remember, the idea is that through shifting adaptive landscapes (changes in their resources, climate, habitat, competitors, etc) exert pressure on a species.  The most successful (fit) individuals pass on their genes to the next generation (passing on awesomeness) while the less fit individuals do not (kill off lameness).  Therefore the next generation is proportionally more fit than the previous one and the pathway continues.  Sometimes there is more than one "equally" fit answer to a given problem or part of the population migrates and is presented with a new set of pressures.  This is (in part) how speciation occurs.  The success of some species over others within the same line and against sister lines is how evolution occurs.

There, now you all survived half of day 1 in my class.

"The most exciting phrase to hear in science, the one that heralds new discoveries, is not 'Eureka!' (I found it!) but 'That's funny ...' " Isaac Asimov