This is the new updated edition of the first book in the bestselling Uncovering Student Ideas in Science series. Like the first edition of volume 1, this book helps pinpoint what your students know (or think they know) so you can monitor their learning and adjust your teaching accordingly. Loaded with classroom-friendly features you can use immediately, the book includes 25 “probes”—brief, easily administered formative assessments designed to understand your students’ thinking about 60 core science concepts.

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The purpose of this assessment probe is to elicit students’ ideas about natural selection. The probe is designed to find out how students interpret the commonly used phrase “survival of the fittest.”

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adaptation, natural selection, variation

The best answer is Lance’s: “I think ‘fit’ means more apt to reproduce.” Size, swiftness, strength, and intelligence are key factors often related to survival, but they do not always determine whether an organism is most “fit” to reproduce and pass its genes on to offspring. The key idea portrayed in the phrase survival of the fittest is that fittest means best suited to survive and reproduce. In some instances, size is an advantage. For example, a large male sea lion is more apt to be the dominant male who breeds with a harem of female sea lions. Because of his impressive size, the females are more attracted to him and the other males are intimidated. Because the other males fear him, he has less competition for food as well. Therefore, he is more apt to survive and reproduce because he can outcompete the other males for food and mates. On the other hand, imagine breeding two dogs. One dog is a very large, muscular, big-boned, fit male. This male is bred to the same type of dog, a petite female. However, the puppies are too large and cannot be delivered without a caesarean section. In this case, the bigger male wasn’t necessarily the fittest. If this had happened in nature, the female dog probably would have died in birth and the male would have lost his chance to pass his genes on to offspring. Examples also exist in the plant world. Flower breeders have developed large dahlias that are prized for their huge flowers. However, these large dahlias must be supported with wires and stakes as they grow because they would fall to the ground and possibly die without support (BSCS 2005). Intelligence, swiftness in escaping danger, and strength are also factors that can contribute to survival, yet they do not always equate with reproductive success.

Elementary Students

In the elementary grades, students build understandings of biological concepts through direct experience with living things and their habitats. They observe and learn about structures, functions, and behaviors that help organisms survive in their environments. They develop an understanding that some organisms are better suited than others to survive in certain environments. They develop precursor ideas to the concept of natural selection, such as the idea that some characteristics are inherited and passed on to offspring. They may have heard the phrase survival of the fittest and equate fit with strength and size.

Middle School Students

Students at the middle level formally develop an understanding of the concept of natural selection. Often the phrase survival of the fittest is used without defining what is meant by fit, thus leading to students’ erroneous misinterpretation of the intent of this phrase. At this level, it is important to develop the idea of variations in populations of organisms that may give some individuals an advantage in surviving, reproducing, and passing on those traits to their offspring. Teaching students about the selection of individuals is the first step in helping them understand natural selection as a mechanism for species’ change.

High School Students

Biological evolution and its mechanism, natural selection, are major focuses of high school biology. At the high school level, students shift from a focus on selection of individuals with certain traits that help them survive to a focus on the changing proportion of such traits in a population of organisms. Their growing understanding of genetics builds on middle school ideas about variation. However, students at this level may still hold on to a misconception that “survival of the fittest” means that “physically fit” species are more fit than smaller ones.

This probe is best used at the middle or high school level. Make sure students have encountered the concept of natural selection before using this probe as is. If they have not encountered this term, consider removing the first sentence from the prompt. This probe is best used to engage students in argumentation about the phrase survival of the fittest and what it means.

• Field-test results of this probe showed that many middle school students are more apt to think of “fit” as big and strong. They relate “fittest” to physical fitness, rather than a species’ ability to survive and reproduce.
• Many people mistakenly think that the biggest individual is the fittest (BSCS 2005).

American Association for the Advancement of Science (AAAS). 2001. Atlas of science literacy. Vol. 1. (See “Natural Selection” map, pp. 82–83.) Washington, DC: AAAS.

Benz, R. 2000. Ecology and evolution: Islands of change. Arlington, VA: NSTA Press.

Biological Sciences Curriculum Study (BSCS). 2005. The nature of science and the study of biological evolution. Colorado Springs, CO: BSCS.

Diamond, J., C. Zimmer, E. M. Evans, L. Allison, and S. Disbrow, eds. 2006. Virus and the whale: Exploring evolution in creatures large and small. Arlington, VA: NSTA Press.

Kampourakis, K. 2006. The finches’ beaks: Introducing evolutionary concepts. Science Scope (Mar.): 14–17.

Scotchmoor, J., and A. Janulaw. 2005. Understanding evolution. The Science Teacher (Dec.): 28–29.

• Have students generate examples of when “bigger is better” in relation to an organism’s ability to survive and reproduce. Then generate examples in which it may be a detriment. Try this with other characteristics to show that there is not one characteristic that always determines fitness for survival.
• Compare and contrast with students the common use of the word fit (as in physical fitness) with the scientific meaning of the word in relation to natural selection. Add this to students’ growing number of examples of the way we use words in our society that are not always the same as the way they are used in science.