Variation within a Population

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Lines of Evidence
for Past Change

The Importance of Variation

1. Variation within a population

Overview

Each team examined a population of fossils - all the same species, a single population, collected at the same time. All showed variation within the population. Teachers were asked to consider the following:

What are some similarities, what are some differences?
What features (characters) can we use to measure similarities or differences
What are your population "subgroups" and how did you determine them?

Responses

Sand dollars
	bell curve distribution of size color variation ratio of height/width consistent
Clams/bivalve (A)
	curve of ridges vary color size 1-4 cm - wide variation of size
Snails (A)
	4-6 cm size color: pale to gray spire, spiral in different directions hatch marks of different types
Clams/bivalves (B)
	1-6 cm sizes two different colors - gray and pink
Limpets
	1.75 cm - 3.5 cm in length different shades consistency in striping distance and number texture varied from smooth to grainy, but grainy only on big ones
Snails (B)
	four types: varied in size from .5 cm - 3 cm three very different looking, like moon snails and were all < 1 cm the rest were conical and similar, but striations running in different directions opening different shapes - some more elongated, some more round

Why is variation important within a population?

With variation, individuals will be different from one another and those differences allow some to survive better than others. With variation, selection has something to work on.