One Long Argument, one hungry blogger

In anticipation of the 150th anniversary of the publication of Darwin’s Origin of Species (November 24th; mark your calendars!), I figured I would address evolutionary theory.  The concept of evolution is one of the simplest in science, yet is often misunderstood.  While searching for a good illustration of how evolution works, I realized that I was hungry.  Heading out to the lobby, I checked the vending machines for something to eat:

 

Noticing the presence of M&Ms in the machine, I had an idea. M&Ms come in different colors; i.e. they have a built-in source of variation.  I opted for the ones with peanuts (E7), put in my dollar, and got a package.  Upon returning to the room, I opened the package of M&Ms, and laid them out to display the degree of variation within said population of M&Ms:

After examining the population, I realized that there was a level of variation such that we have a healthy population, with some traits being rarer than others.  Blue, Green, and Orange were designated as “common”, Brown as “uncommon”, and Red and Yellow as “rare”.  So we have a population with variation.  How does said population evolve?

Certain traits (in this case colors) are advantageous, while others are disadvantageous.  If a predator likes to eat red things, the red M&Ms are in trouble.  There is only one representative of that variety in our population, and this blogger does like red M&Ms.  Therefore, we have a disadvantageous trait, and said variety is removed from the gene pool, i.e. it goes extinct.

While the red variety goes extinct, the blue, green, yellow, and orange varieties go on living happily, and breeding (unfortunately I cannot make M&Ms reproduce…bear with me).  Eventually, some event occurs that alters some portion of our population (be it a behavioral change, mutation, etc).  In this case, we’ll use a reference to 2001 A Space Odyssey.  A monolith pops into the scene.  The blue and orange M&Ms are attracted to it.  The other M&Ms run away:

 

 

If you are not familiar with the scene this is referencing, it is available here.  So the Blue and Orange varieties gain some sort of differential survival advantage (call it “intelligence”) from contact with the monolith.  We’ll say that the monolith is radioactive and caused rapid mutations within the Blue and Orange genomes; we’re not looking at long periods of time here, so I’m taking a leap here and increasing the speed of our demo.  The Blue and Orange varieties chase off the other varieties of M&Ms due to their inherent differences (we’ll say through a mountain pass), and then return to their own region.  A landslide (or in this case a giant screw falling in the middle of the picture) blocks off the pass, separating the blue and orange varieties from the other varieties:

After separation, you have two separate varieties, which compete amongst themselves, and evolve along separate paths.  This is called allopatric speciation:

Eventually, an earthquake or something of the sort removes the geographic barrier, and the populations mix once again:

If the two populations have been separated long enough, and evolved along different enough lines, then they will be able to coexist without competition.  If this is the case, populations will stabilize between the two without much competition:

 

OK, but what has this little thought experiment demonstrated about evolution?  Evolution through natural selection, at its most basic level, requires variation within a population.  When dealing with living organisms, this variation is provided by genetic mutation.  Genetic mutation is pretty much random in nature.  However, certain mutations are favorable for survival, other mutations are unfavorable, and some are neutral.  Darwin’s model of natural selection is based on a competition for resources; certain individuals will just be better able to compete for resources.  These individuals are the ones that will tend to leave the most offspring.  Natural selection works by weeding out unfavorable mutations and increasing the population of organisms with favorable mutations.  Mutation is random.  Natural selection is not.  Natural selection will inherently favor those organisms that have traits which give them an edge for survival.  In our M&M analogy, if predators like to eat red M&Ms, then red M&Ms will likely be rarer (or go extinct quicker) than other varieties.  If some gazelles run faster than others, and the slow ones are the ones that generally get eaten by lions, then natural selection will gradually increase the average speed of the gazelle population as a whole.
Within our M&M analogy, we saw a rapid “Poof”-style evolutionary shift in which some M&Ms drastically changed form after coming into contact with a monolith.  I do not mean to imply some sort of magical evolutionary process in which a bird suddenly hatches from a lizard egg; that’s saltationism, and saltationism is wrong.  However, given the right conditions and environmental pressures, evolution can happen relatively quickly.  When you separate one large population into two smaller ones (our screw-landslide), you decrease the size of the gene pool, and thus enlarge the potential impact of a given mutation.  As such, relatively small populations can often change relatively quickly.  In some cases, once the separated populations come back into contact with each other, they have evolved along separate enough paths that they do not directly compete with each other, allowing for the coexistence of both groups.  In other cases, both groups do still directly compete with each other.  In these cases,  natural selection once again weeds out certain individuals, and allows others to prosper.

As demonstrated, evolution through natural selection is an extremely simple process. Some organisms are better adapted than others, and these well-adapted organisms will tend to reproduce more often, eventually taking over the population. However, as demonstrated through our brief, rough look at allopatric speciation, natural selection is not the only force involved in controlling the evolution of life on Earth.  Environmental factors also can play a major role.  Barriers between populations are also important.  Meteor impacts and other mass extinction events can drastically shift the course of evolution on Earth.  But can evolution explain the diversity of life on Earth?

Given the long period of time for which the Earth has existed (approximately 4.6 billion years), we certainly have had enough time to evolve the diversity of life on Earth.  While some have raised questions (generally pseudoscientific in nature) about the ability of evolution to explain the origin of the eye, or transitions between major groups of animal, for example, these objections are weak.  While we have a working mechanism for evolution, and a huge amount of evidence in support of the idea that life on Earth is the result of a long, drawn-out process of evolution, there is no mechanism given for these arguments against evolution.  No defined laws which would forbid the evolution of the eye.  No tactile reason to believe that one could not evolve a bird from a dinosaurian ancestor, or an amphibian from a fish.  The evidence is clear, and the process is as elegant as it is simple.  Evolution happens.

 

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4 Comments on “One Long Argument, one hungry blogger”

  1. jg Says:

    Delightful post.
    Your last paragraph reminded me of a question I’ve had a long time. What is a common rate of speciation? I suspect that I’ve misunderstood the few estimates I’ve heard. I know Chichlid fishes and some south African ice plant-like thing have high documented rates, but I see 500 million years of multicelled life too short for the vast diversity we see and have lost over that time.

    thanks
    jg

    • darwinaia Says:

      Hey John,

      Sorry about the slow response time. Travelled back to New York over Thanksgiving break, so I’ve been out of it for a bit. As far as rates of speciation, they change based on a few factors.

      First, there’s the question of mutation rate. When you couple that with average length of a generation of the species in question, you get a large amount of variability there. answers.com actually has a pretty good basic discussion of this aspect ( here http://www.answers.com/topic/mutation-rate ).

      The second major variable is the environment. Is the species in question in a highly populated, diverse region? If yes, then the most likely evolutionary strategy would be to for the species to stick with one niche that works, and change in response to external pressures (either other environmental factors or competition within the niche). In situations like this, you’d expect a relatively slow rate of change if the species in question was well-adapted and did not recieve a large amount of competition (think Coelocanths).

      In other cases, you can end up with species that have broken into a new area in which there is a relatively weak ecosystem with many niches left unfilled. You’d expect more rapid speciation in events such as this, since you’ve got the possibility of more mutations proving beneficial, especially if they allow some members of the parent species to branch off and fill one of these empty niches. Mass extinctions are actually great producers of biodiversity for this reason; if you empty out most of the major niches in an ecosystem, there’s more room for the remaining organisms to diversify.

      Essentially, you’d expect rapid speciation right after mass extinctions, and relatively slow speciation in more densely populated ecosystems. With these denser ecosystems, the emphasis would be on holding one niche well, while with ecosystems devastated by extinction you’d have more room for change.

      It’s a complex enough system that its difficult to develop an overall average rate of speciation; from what I’ve seen, you even get variation in rates of speciation within genuses. I wish I could give you a better answer here, but you’ve hit on one of my weaker areas.

  2. darwinsbulldog Says:

    Evolution makes me hungry…


  3. vending machines are great pieces of technology that we enjoy today, they are made for the purpose of giving us convenience “”


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