Natural Selection and Genetic Drift | Experiment

Camouflage Lab

• Eduardo Pérez

Introduction

In 1859, an English scientist named Charles Darwin published his book, On the Origin of Species. This book described his Theory of Evolution, the process by which populations of organisms change over time to adapt to their environment. Over the years, the Theory of Evolution has become one of the most well-supported and widely accepted scientific theories out there.

The main purpose of this experiment is to show how natural selection and genetic drift look like when they are put into play. According to Dennis O’Neil, anthropology professor at Palomar College, natural selection is a series of events by which some organisms are born with random variations of a specific genetic trait that gives those organisms an advantage in “staying alive long enough to survive and successfully reproduce”. [HS1]Over time, these organisms will have more offspring, causing a shift in the population to that trait (O’Neil 2013). An example of natural selection is the finches of the Galapagos Islands. Each island has different food sources, and each species of bird has slightly different beaks that are better suited for consuming their food source. In his book, Life: The Science of Biology (2014), author David Sadava describes genetic drift as the “random fluctuation of gene frequencies in a population due to chance events.” An example of genetic drift would be an oil spill in a river populated by fish. The surviving fish will repopulate the river with their offspring who share the same genetic variations.

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In this experiment, small beads were put on a colored mat to represent mussels in their environment. In the first part of the experiment, one team member was assigned as the “Oystercatcher” and they selected beads one by one and removed them from the environment to represent natural selection. In part two, beads were randomly removed by a pencil wrapped in tape (a piece of driftwood calling with mussels and killing them) which represented genetic drift. Both parts of the experiment were repeated for three “generations” after the surviving mussels repopulated the environment. The question being tested in this experiment was: How do natural selection and genetic drift affect populations of organisms? I hypothesized that the blue and red beads would be the most commonly selected and removed in the first part of the experiment, and that the beads would be removed in equal numbers by the pencil wrapped in tape.

Materials and Methods

The two most important materials used in this lab were the small colored beads, and the mat. Blue, white, green, and purple beads were used to represent mussels with different traits. Ten beads of each color were placed in the “environment” to start the experiment. The environment for the mussels was represented by the mat with a random background printed on it to camouflage the beads. For the second part of the experiment, a pencil was wrapped with masking tape (sticky side out), and used to represent a log crashing into the environment. The pencil was rolled along the mat to randomly pick up beads.

To start off the experiment the person designated as “oystercatcher” removed beads one at a time from the mat and placed them in petri dishes (independent variable). The oystercatcher was instructed to pick the first beads they saw, and to look away from the mat between selections. After 30 beads were removed and placed into a petri dish, the survivors were counted (dependent variable). The numbers of each color of bead was recorded, and that number of beads (x) plus 3x beads were added back to the mat to represent the repopulation of the species based on the number of survivors. These steps were repeated two more times, and the data recorded each time.

In part two of the experiment, the pencil wrapped in tape was rolled along the mat to randomly select and remove beads until 30 beads were removed (independent variable). Then the same procedure used in part one to repopulate the environment was used in part two (dependent variable). These steps were repeated two more times, and the data was recorded.

Results

I. Population of mussels over 3 generations after natural selection from Oystercatcher.

When the beads were removed by the oyster catcher, the blue beads were completely removed from the map in just one generation, and the purple and white beads were also driven extinct, but not until the second generation, leaving only green beads at the end of the three generations.

II. Population of mussels over three generations after genetic drift from log colliding with habitat.

When the beads were removed by the log, the survivors were more random and more equal than when removed by the oyster catcher. By the end of the experiment however, a majority of the survivors were yellow beads.

III. Population of mussels over 3 generations after natural selection from Oystercatcher.

IV. Population of mussels over three generations after genetic drift from log colliding with habitat.

Discussion

In part one of the experiment, where the beads were selected and removed by the oystercatcher, the blue beads were immediately driven extinct, and the white and purple beads were driven extinct in only one more generation. This left only green beads by just the third generation. These results show that in natural selection, organisms chances of survival are based on how fit they are to survive in their environment. In this experiment, the blue beads did not blend into their environment very well, and they were eliminated immediately. The purple and white beads were also poorly camouflaged, and were eliminated very quickly as well. Even by the third generation, where there were only green beads left, the oystercatcher had a hard time finding 30 beads to remove, because the green beads were much more difficult to see in the environment. These findings could be applied to a real life environment, and used to predict how well certain organisms have adapted to their environment, and how an entire population will change over time because of natural selection.

In part two of the experiment, the number of survivors was much more equally spread out between the different colors of beads. Although there were definitely more yellow beads than anything else by the end of the experiment, this outcome would be different every time you repeat the experiment, based on the survivors from earlier in the experiment. These results are consistent with the principles of genetic drift, where organisms are eliminated randomly from a population based on random occurrences like natural disasters and diseases. If for example, lightning struck an area with a high concentration of a particular type of mussel, over time, the number of that mussel would decrease because there are fewer mussels to reproduce.

This experiment was limited to the use of basic lab materials in a lab setting, but it accurately represents data that would be collected from an actual environment out in nature. This experiment was only able to demonstrate the effects of color and camouflage on the survival rates of an organism, but in reality, there are many other genetic variations which contribute to the fitness of an organism to its environment. An elephant, for example, may not be particularly well camouflaged, but its sheer size and strength help it to survive. Further research could be done to demonstrate the effects of other forces of evolution, as this experiment only involved genetic drift and natural selection.

Conclusion

The data in this experiment supports the hypothesis that the blue and purple beads would be the most commonly eliminated by the oyster catcher, but the yellow beads were also driven extinct, leaving only green beads. The data somewhat supports the hypothesis that the beads would be removed in equal numbers by the log, although the population shifted to a majority of yellow beads by the end of the experiment. The same experiment could be repeated several times to obtain more data to prove or disprove this hypothesis.

References   

O’Neil, D. (2013). Early Theories of Evolution: Darwin and Natural Selection. Retrieved August 29, 2016, from http://anthro.palomar.edu/evolve/evolve_2.htm

Sadava, D. E. (2014). Life: The science of biology (10th ed.). Sunderland, MA: Sinauer Associates.

[HS1]Are these his exact words? If not, remove the quotes