What we learned this week

This week we learned the difference between and how to calculate standard deviation and standard error. I struggled a bit at first to really understand what these two numbers meant in the context of a data set, but made sure I at least somewhat knew what they were before Friday’s quiz. We then discussed the five pathways of evolution, and looked at examples of evolution in galapagos finches and desert pocket rock mice. We watched clips of a documentary and completed worksheets for each. Finally, we took notes on how the theory of evolution was developed and who contributed to it. Most of the scientists and ideas sounded familiar from freshman-year biology, but a refresher never hurt anyone. Most of these notes and the topics covered this week related to Big Idea #1.

Five Types of Evolution

These categories are how we learned to classify types of evolution, or a change in a population over time. I thought it was interesting that evolution could be influenced in so many unique ways, not limited to natural selection and mutations.

• Natural Selection
  • The process by which those organisms with traits best fit to the environment survive and reproduce more than those with less suitable traits. This causes a change in the population over time that favors the fitter traits.
• Mutation
  • Errors that occur while reproducing genetic material. Mutations can either be positive, negative, or most commonly, neutral. The most visible kind of mutation are positives, as neutral mutations do not usually have any effect and organisms with negative mutations wont be able to compete as well and will die out. Positive mutations will cause a change in a population as their organisms will have a competitive advantage over their brethren.
• Preferential Mating
  • Change in a population caused by organisms preferring to choose mates with certain favorable traits.
• Migration/Gene Flow
  • When populations of organisms move from one area to another, this causes change in the  makeup of the populations of both the old and new areas. If there is a population of 50 geese with red feathers on a lake, and 25 more geese with blue feathers are forced to move to the lake, the population of the lake has changed from 100% red to 2/3 red, 1/3 blue.
• Genetic Drift
  • Chance changes to a population. If all the blue geese from above happen to be struck by meteors, the population makeup has changed, but only by chance.

Beaks of Finches, Shades of Mice

The primary examples of evolution we focused on this week were in galapagos finches and rock pocket mice populations. For the finches, we observed how different beak sizes in differing situations performed better or worse, like in the drought of 1976. The effects of the drought caused large seeds, the food of big-beaked-birds, to become scarce. This forced the BBB’s to eat smaller seeds, which their large beaks were not very good at. Here we can see that the birds with smaller beaks have become more competitive as the environment changed, and the surviving proportion of birds with smaller beaks was accordingly larger than before the drought. In the documentary we were introduced to the scientists who had dedicated much of their life’s work to catching, tagging and tracking hundreds of finches in order to observe this. This was a good example of evolution caused by natural selection.

We were presented with a similar story in the case of the rocket pocket mice. These mice lived in the deserts of Arizona, and were well camouflaged to blend in to the light-colored ground. This changed when a few thousand years ago volcanic eruptions took place nearby, spreading great lava flows out over the desert which cooled into slabs of black rock. The brown-colored mice now stood out in high contrast with the black earth, and so were easy picked off by predators like hawks and owls. The mice did not go extinct on the lava flows, however, as a few were born with a mutation that would have been a disadvantage back in the desert. This mutation effected the gene that controlled the mouse’s production of melanin, the protein that causes the dark color in mammal fur and skin. The mutated mice were dark in color, blending in to the dark lava flows. Sure enough, after several generations nearly all mice living on the flows were black. This was another simple example of natural selection, but also displayed how beneficial mutations can quickly change a population.