Lab evolution

Biology 1, Philippine Science High School – Main Campus
Laboratory Activity # 2: EVOLUTION
The lives of organisms are coupled with the environment both on a short and long time scale. Responses of
organisms within a short time scale are associated with the relationship of an individual organism with its environment.
Within a long time scale, we need to go beyond the individual level and consider what happens to groups of individuals in
response to particular conditions in their environment.
In nature, organisms do not exist alone. They are always in association with other individuals of the same or of
different species. This collection of organisms of the same species occupying a defined geographical area is referred to as
a population.
Individual members of a population are not identical. They may vary in color, size, rate of growth, and tolerance
to drought or high temperature, to name a few examples. Some of these traits vary due to direct physiological,
morphological, or behavioral responses of organisms to their environments. Environmentally controlled traits are non-
heritable. Heritable traits, on the other hand, are those which can be passed on from parents to offspring.
In humans, characteristics such as color of the skin, eyes, and hair are common examples of heritable traits. The
Filipino population can therefore be described as predominantly brown-skinned with dark eyes and dark hair. The gene
and gene frequencies of a population may change over long periods of time. When this change happens, evolution is said
to have occurred. Evolution is therefore simply defined as a change in the gene frequencies of a population through
generations. Evolution occurs when population composition changes.

Objectives:
1. To distinguish between heritable and non-heritable traits of individuals within a single population.
2. To understand the process of natural selection and the concept of adaptation.

Materials: (to be provided by the teacher, except for those marked *)
sticks of various colors plastic containers watch/timer*

PART A. Procedure for heritability of variable traits within a population :
1. Before beginning this exercise, construct a table where you will record your data. Read through these
instructions first so you will have an idea how your table should look like.
2. Search the Internet for published data on ‘degrees of heritability’ or ‘heritability estimates’. Notify your teacher
(through email or in class) about sites you wish to include in the whitelist. Take note that inclusion of such sites
in the whitelist may not be immediate, thus allot ample time for research.
3. From the available data, choose three plant species and three animal species. List these in your data table.
4. For each species, list down three traits and their degree of heritability. Specify whether the trait is genetically or
environmentally determined. A genetically determined trait has a high heritability value ( 0.5 or 50%), while an
environmentally determined trait has a low heritability value ( 0.50 or 50%). Write these down in your data
table as well.

PART B. Procedure for natural selection in action:
Field work
1. Before beginning this exercise, construct a table where you will record your data. Read through these
instructions first so you will have an idea how your table should look like.
2. Obtain colored sticks from your teacher; these sticks represent individuals in a population. Count 10 individuals
of each color (red, green, and natural color). Place all 30 sticks in a plastic container and mix them well. Note
that the population composition starts out with equal proportions of the different colored individuals. Your data

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table should include the initial count (10) and the initial proportion (0.333) of each color of stick, as well as the
total count (all colors of stick = 30) and a sum of the proportions (=1.000).
3. Locate a 10 sq. m. portion of sandy/rocky area within the PSHS campus. Scatter the sticks within the area;
members from other groups may help in scattering the sticks.
4. Place the emptied container at the center of the 10 sq. m. area. The container will serve as the “catching
ground”. Assign two members of your lab group to collect the dispersed sticks and to deposit these in the
catching ground within the span of 60 seconds. Sticks should be collected then deposited only one at a time, and
there should be no running in the process. The third lab group member will monitor the time and record the
data as “Final Prey Caught” or FPC. Only undamaged or slightly damaged sticks should be considered during the
counting of FPC. Provide a space in your table for the FPCs of other groups as well.
5. Repeat Steps 3 and 4 in a grassy area. Record these data in a separate table.
*Before starting a new round of dispersing and collecting sticks, make sure all sticks were retrieved from the
previous dispersion and collection; members from other lab groups are encouraged to help in retrieving
uncollected sticks.

Data collation
6. ‘Group data’ should now be combined into ‘class data’. Thus, the initial individual count of each color of stick
would now be 100, with a total population of 300 sticks. The FPC of each color of stick will now be equal to the
FPCs of that color of stick for all groups. Record these data in a new table, still indicating the initial proportions
of each color of stick.
7. Determine the number of “Final Prey Survived” or FPS for each color by subtracting the FPC from the initial
count of 100. Record this in your table and include a row for the sum of the three values of FPS.
8. Compute for the “Final Proportion” or FP of each color of stick by dividing that individual FPS by the total FPS.
Record this in your table.
9. Compute for the “Expected Prey Survived” or EPS by dividing the total FPS by 3. The EPS will be the same value
for all three colors of stick. Record this in your table.
10. For each color of stick, square the difference of the FPS and the EPS, then divide this by the EPS. Add the three
values (one for each color) that you get and record this total in your table. This sum is called the 2 value.
11. Determine if the changes in the population are significant by referring to the values below:
Not significant ( 2 5.99) Significant (5.99 2
9.21) Highly significant (9.21 2
)
What you have just performed is a statistical test known as the chi-square (“kigh square”) test.

Worksheet
1. For the worksheet of this activity, use short bond paper (8.5” X 11”). Note that if you are printing your work at
the library, you will have to provide your own paper since they only have A4 (8.27” X 11.69”). Your work should
be computerized and should include the following information: section and group number, class number and
name of each member, date(s) performed, and date submitted.
2. The worksheet consists of two parts: (I) the Results Section and (II) the Discussion Section.
I. Results Section: This section should include all the tables that were required of you in this activity.
II. Discussion Section: Write your answers to the following questions.
1. Compare the heritability of traits between plants and animals.
2. Compare and contrast environmentally determined traits with genetically determined traits.
3. Is evolution by natural selection occurring in the stick population? Explain your answer.
4. Which individuals (green, red, or natural) have the higher fitness? Do the same individuals have the
same fitness in different environments? Explain your answer.

Modified from:
Caldas, M.P., V.C. Cuevas, Z.N. Sierra, C.R. Cervancia, and M.T. Zafaralla. 2000. Laboratory Guide in Ecology. Environmental Biology
Division, Institute of Biological Science, CAS, UPLB Pub. p. 1-6.

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