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Zack Brown
Anthropology 1020
Signature Assignment: Darwin’s Finches
Introduction
Darwin’s Finches are a group of closely related birds, 14 species with the same common
ancestor on the Galapagos Islands (Soons, 1093) . The birds are referred to as called Darwin’s
Finches because Charles Darwin famously collected them on his voyage to the Galapagos
Islands as he was developing the theory of evolution by natural selection. The story of him
finding the birds and immediately noticing the variation of their beaks is apocryphal, but has
come to symbolize the development of the theory of natural selection in the way that an apple
falling on Newton’s head symbolizes the development of the theory of gravity.
The Galapagos Islands are an extraordinary playground of natural selection. Darwin’s
finches are important and are still heavily studied today. The Earthwatch Institute summed up
the finches’ importance well: “These finches are considered to be the world’s fastest-evolving
vertebrates because their appearance and behavior quickly adapted to this closed and rapidly
changing environment” (Darwin’s Finches and Natural Selection). The finches’ variety of beak
type shows the way the finches have adapted to their environmental conditions. Darwin would
later write this about the finches, "Seeing this gradation and diversity of structure in one small,
intimately related group of birds, one might really fancy that from an original paucity of birds in
this archipelago, one species had been taken and modified for different ends” (Charles Darwin
and Evolution).
The wild variation in beak type among the closely-related finches is the topic of much
scientific research and testing. One study I read, Mechanical Stress, Fracture Risk and Beak
Evolution in Darwin’s Ground Finches (Geospiza), investigates the “fracture-avoidance”
hypothesis. The fracture-avoidance hypothesis is essentially that the ground finches (Geospiza)
have developed wider and taller beaks mainly for the purpose of fracture avoidance (Soons,
1093)—i.e., basically the functionality and durability of their beak in the hard environment. To
test their hypotheses, they developed “finite-element models” (FEMs) of the upper beak in
ground finches (1094), collected, dissected, and CT-scanned several specimens, including the G.
fortis, G. fuliginosa and G. scandens. The tests supported their hypothesis that “tall and wide”
beaks handle pressure better and are more conditioned for fracture avoidance: “Tall and wide
beaks seen in G. fortis, G. fuliginosa and G. magnitrosis are seen to distribute the load applied to
the beak with lower peak stress values” (1096). The data reinforced their hypothesis that beak
morphology “should evolve in concert with the force generating capacity of the jaw adductors
through selection for the capacity to avoid structural failure under conditions of increased muscle
and food reaction force” (1097).
In class, we’ve been studying evolution by natural selection, and performed our own little
experiment to demonstrate adaptive success in natural selection as seen with Darwin’s Finches
beak types. The experiment itself is simple: using a variety of beak apparatus, each student
competed against his peers to pick up as many sunflower seeds as she could and place said
sunflower seeds into the apaper cup. There were five rounds. At the end of each round, the seeds
were counted up, and the three birds/students with the lowest amount of seeds were sent into
Loser’s Corner, and the top three seed gatherers were sent into the Winner’s Corner. The most
effective beaks—the beaks with the most fitness—would replace the least effective beak and
quickly grow and become the dominant species. When a bird/student lost, this would represent
her beak not being a favorable trait, and therefore would being passed on to the next generation,
and that species would go the way of the dodo.
My initial hypothesis for the experiment was that the clothespin beaks would increase in
frequency as the experiment went on. My rational was that the clothespin would be effective at
picking up sunflower seeds, and would be favored by natural selection. My rational for this
hypothesis was that the clothes pin beak had an inherent advantage for collecting resources, i.e.,
the clothespin seemed like an apt tool for picking sun flower seeds off a desk and placing them in
a paper cup at a clip faster than the completion.
Materials and Methods
Our experiment included sunflower seeds, paper cups, and several variations of “beak” types
in order to test which would be the most successful and have the most adaptive success. The
beak types were: tongs, clothespins, chopsticks, binder clips, tweezers, chip clips, large hairclips,
and, introduced as a mutation in the third round, a small hairclip. Also, willing volunteers would
be necessary to recreate the experiment.
The “beaks” or beak-like apparatuses, were distributed to the students (one student per beak).
The base level of our experiment introduced an environment of 2 tongs, 5 clothes pins, 5
chopsticks, 5 binder clips, 5 tweezers, 5 chip clips, 5 large hairclips. A single small hairclip was
introduced in round 3. The sunflower seeds had been distributed unevenly, more or less
randomly. In a later round, more sunflower seeds were introduced into the environment. It had
been a good season. There could have also been a drought; this was done to represent selective
pressures, the environments effect on the fitness of traits.
Results
Beak Types
Beginning Round 1 Round 2 Round 3 Round 4 Round 5
Tongs
2
3
3
3
3
3
Clothes Pins
5
5
7
8
9
10
Chopsticks
5
5
4
3
2
1
Binder clips
5
3
3
1
1
1
tweezers
5
5
5
5
5
5
Chip clips
5
2
6
6
8
9
Large hairclip 5
5
5
5
4
3
The most
favorable
beak was
the
clothespin.
The beaks most suitable to the gathering the seeds quickly increased in number. The
clothespins and chip clips were the most successful beaks, clothes pins having the greatest,
finishing with 10 clothespin. Several species just got by throughout the experiment—passing on
their beaks to the next generation, but not exactly flourishing. The tongs (the most surprising
variation began with 2 tongs, finished, somehow, with 3); the tweezers started with five members
of its species and finished with five members of its species. Three species suffered severe
declines: the chopsicks—started with 5 and ended with 1—the binderclips, started with and
ended with 1 surviving member of the species, and the large hairclip, started with five and ended
with 3 surviving members. The small hairclip mutation, which happened in round three, turned
out to be not a favorable mutation at all: the small hairclip went extinct by the end of the game,
lost forever, not but a footnote in history.
12
10
Tongs
Clothes pins
8
Chopsticks
Binder Clips
6
Tweezers
Chip Clips
4
Large Hairclip
Small Hairclip
2
0
Beginning
Round 1
Round 2
Round 3
Round 4
Round 5
Frequency of beak success
Conclusion
My hypothesis that the clothes pins would increase in frequency was supported by the
experiment. Our data shows that clothe pin was indeed a favorable trait; it consistently improved
in frequency after the second round, and the clothespin had doubled in number by the final
round.
There were some outside factors that the experiment can’t account for, and more tests would
have to be run with a different test group before the data could say which is really the most
effective beak. For instance, the experiment was done on the honor system—there were no
official observers or cameras. A test subject/bird could have simply lied about how many
sunflower seeds they had gathered. Another outside factor to be considered is the variation of
skill level in the test subjects, e.g. the chopstick beak might have fared better or worse depending
on the student’s ability with chopsticks. The way the beaks are used by individuals would create
interesting variations that, in the data of this single experiment, is hard to account for. There
were also environmental factors that could yield different results. All the beaks were handed out
in sequence, meaning that the chopsticks all sat next to each other, the clothespins inhabited one
location, etcetera. The seeds could have been unfairly disturbed onto their desks.
Running the experiment again with other students would likely yield very similar results—
the most effective beak types are the most effective beak types—but there would be variations
and anomalies.
Discussion
The scientific method is used to objectify facts. By identifying a problem or an unproven
idea, proposing an hypothesis, accurately collecting and analyze data, and assessing whether the
data supports or falsifies the hypothesis. The scientific method is an effective tool for analyzing a
situation and trying to parse facts from baseless speculation. I would argue that most fields use
the scientific method in some way or another. A detective, for example, uses the scientific
method: she makes an assessment that is plausible—Mr. Blue did it in the dining room with a
candle stick, whatever—then has to follow up on her hypothesis by further investigating the
crime, collecting data, and piecing together clear facts. The detective would then have to make
an assessment about whether the evidence supports her original hypothesis. This experiment
demonstrated the scientific method because I proposed a hypothesis that was a plausible
assumption (in this case, that clothespins would be an effective tool for picking up sunflower
seeds), and tested the hypothesis by performing an experiment and gathering data. I then
evaluated the data and assed that it supported my hypothesis.
The theory of evolution by natural selection explains how characteristics are passed on from
generation to generation. This activity demonstrated how favorable traits are passed on to the
next generation while unsuccessful ones die out. Natural selection is cruel, if you had an
unfavorable beak, you stood no chance.
References:
Soons, J., A. Herrel, A. Genbrugge, P. Aerts, J. Podos, D. Adriaens, Y. De Witte, P. Jacobs, and
J. Dirckx. "Mechanical Stress, Fracture Risk and Beak Evolution in Darwin's Ground
Finches (Geospiza)." Philosophical Transactions of the Royal Society B: Biological
Sciences 365.1543 (2010): 1093-098. Web.
"Charles Darwin & Evolution." Charles Darwin & Evolution. Web. 07 Feb. 2015.
http://darwin200.christs.cam.ac.uk/pages/index.php?page_id=b6
"Darwin's Finches and Natural Selection in the Galapagos." Darwin's Finches and Natural
Selection in the Galapagos. N.p., n.d. Web. 06 Feb. 2015.
http://earthwatch.org/expeditions/darwins-finches-and-natural-selection-in-the-galapagos