Essential Science for Teachers: Life Science
Variation, Adaptation, and Natural Selection Children’s Ideas
Children’s Ideas About Variation, Adaptation, and Natural Selection
Below are common ideas children in grades K-6 have about this topic, compiled from research on children’s ideas about science (see the Session 5 Children’s Ideas Bibliography). Consider what evidence might refute this idea, and why a child would be likely to believe this?
1. Variation has little to do with evolution.
Evolution is defined as change in a population over time. This implies that evolution can only be observed if some version of a trait — like hairiness or height in plants — becomes more common over many generations. Variation is thus a condition for evolution. Evolution is an abstract concept and one that children — and adults — are unlikely to ever observe. What can make sense to children is the possibility that certain variations may help an individual survive and produce more offspring. This may be a first step toward understanding evolution.
2. The environment is the cause of variation among individuals.
Individual variation exists even when the environment is kept constant. In the video, the growth conditions for the Fast Plants in Kathy Vandiver’s class were controlled, yet plants of the same species varied greatly. Children readily observe individual variation. If they have not been introduced to the basics of heredity (i.e., DNA and genes), then they are likely to account for individual differences by considering what might vary around that individual: the environment.
3. The environment is more important than genes in causing variation.
If the environment were more important than genes in causing variation, even subtle changes in the environment would be expected to have an impact on any number of traits. Yet despite constant changes in the environment, very little change occurs in individuals as a result. If children have a basic understanding of the genetic basis of heredity, they may still believe the environment has a greater role in causing variation because they have a hard time believing that there is so much variability resulting from genes alone. Since they can’t observe variation in genes, and they can observe variation in the environment, they may conclude that the environment has a greater impact. They may also have had experience manipulating conditions that have dramatic effects on plants — this could influence their early ideas about the environment vs. genes.
4. Sexual reproduction is not recognized as a source of variation.
If you look at the offspring of any two parents, you’ll notice that each varies from the other (except in the cases of identical twins and clones). Offspring receive hereditary information from both parents, and this information varies. Consider a litter of puppies: each was formed from one sperm and one egg from the same two parents and each developed in the same environment, yet the puppies will still vary. It therefore makes sense to conclude that some aspect of sexual reproduction — in this case, different information in different sex cells — is responsible for the variation in the puppies. Children can easily understand the basics of sexual reproduction — offspring form from two parents. They can also easily observe that individual offspring from one set of parents vary. Still, young children may not at first connect the mechanism of reproduction with why individuals vary.
5. Traits are inherited through the “blood” or “brain.”
Reproduction involves the transfer of hereditary information through a physical structure — the molecule DNA. No part of the blood or brain is involved in this transfer. In sexually reproducing organisms, this transfer occurs through the sex cells. Children who have not yet been introduced to the basics of sexual reproduction — that it requires two parents and involves information that is transferred in sex cells — are likely to account for heredity in ways that directly connect a female parent to its offspring. Blood, in particular, is a likely explanation.
6. Mutation results in undesirable (e.g. “monstrous”) traits.
A mutation is an error in the replication of DNA before it is passed to a daughter cell — whether this is a body or sex cell. Mutations result in new information in the genes, which can result in new variation in a population. Variation, in turn, allows populations to evolve. Even new variation can potentially be beneficial. If this weren’t so, every time mutation occurred, the result would be a poorly adapted individual (or a “monster,” as children may think of it). Populations would not survive. Mutation as a source of variation is an advanced concept in the study of heredity so it is not surprising that children have little context for understanding it. The basis for believing that mutation results in monsters is likely derived from movies and television.
7. Adaptation involves individuals changing in response to their environment in order to survive.
In an evolutionary sense, adaptation occurs over many generations and involves change in a population. It is observed when some variation in a trait becomes more common with each generation. This is different than the responses that an individual might make in order to survive during its lifetime. The first meaning that children have for the word adaptation will often involve a change that an individual makes. To build an understanding of adaptation as an evolutionary concept, children might be encouraged to consider two or more generations of a population that have changed in ways that make each successive generation better suited to its environment than the previous one.
8. Individuals adapt out of need or desire.
Adaptation has a genetic basis. Need or desire to change (i.e., vary) in some way in order to survive has no impact on the information that is already present in an individual’s genes. This reflects anthropomorphic reasoning: People can consciously decide to change, therefore change comes about because of need or desire. One way to counter this idea in terms of evolution is to encourage children to think about other life forms that cannot think — like plants.
9. Traits that are developed during an individual’s lifetime can be passed on to their offspring.
In order for traits to be passed to offspring, they must be coded in a parent’s DNA and then transferred during reproduction. Traits that are developed during a lifetime, such as a muscular build or the ability to speak several languages, do not have an impact on one’s DNA. Children who understand that offspring inherit traits from their parents may extend this idea to traits that a parent develops during his or her lifetime. It may be difficult to challenge this thinking with traits that have a genetic basis — one’s build, for example. Encouraging children to think about someone who has dyed his or her hair or who has learned how to swim may help challenge this thinking.
Children's Ideas Bibliography
The Children’s Ideas listed in this section of the Web site were compiled from the following research:
- Bishop, B. & Anderson, C. (1990). Student conceptions of natural selection and its role in evolution. Journal of Research in Science Teaching, 27(5), 415-427.
- Brumby, M. (1979). Problems in learning the concept of natural selection. Journal of Biological Education, 13(2), 119-122.
- Deadman, J. & Kelly, P. (1978). What do secondary school boys understand about evolution and heredity before they are taught the topics? Journal of Biological Education, 12(1), 7-15.
- Driver, et al. (1992). Life and living processes. Leeds National Curriculum Support Project, Part 2. Leeds City Council and the University of Leeds, UK.
- Engel Clough, E. & Wood-Robinson, C. (1985). Children’s understanding of inheritance. Journal of Biological Education, 19(4), 304-310.
- Settlage, J. (1994). Conceptions of natural selection: A snapshot of the sense-making process. Journal of Research in Science Teaching, 31(5), 449-457.
Session 1 What Is Life?
What distinguishes living things from dead and nonliving things? No single characteristic is enough to define what is meant by "life." In this session, five characteristics are introduced as unifying themes in the living world.
Session 2 Classifying Living Things
How can we make sense of the living world? During this session, a systematic approach to biological classification is introduced as a starting point for understanding the nature of the remarkable diversity of life on Earth.
Session 3 Animal Life Cycles
One characteristic of all life forms is a life cycle — from reproduction in one generation to reproduction in the next. This session introduces life cycles by focusing on continuity of life in the Animal Kingdom. In addition to considering what aspects of life cycles can be observed directly, the underlying role of DNA as the hereditary material is explored.
Session 4 Plant Life Cycles
What is a plant? One distinguishing feature of members of the Plant Kingdom is their life cycle. In this session, flowering plants serve as examples for studying the plant life cycle by considering the roles of seeds, flowers, and fruits. A comparison to animal life cycles reveals some surprising similarities and intriguing differences.
Session 5 Variation, Adaptation, and Natural Selection
What causes variation among a population of living things? How can variation in one generation influence the next generation? In this session, variation in a population will be examined as the "raw material" upon which natural selection acts.
Sessions 6 Evolution and the Tree of Life
Why are there so many different kinds of living things? Comparing species that exist today reveals a lot about their relationships to one another and provides evidence of common origins. This session explores the theory of evolution: change in species over time.
Session 7 Energy Flow in Communities
Communities are populations of organisms that live and interact together. The structure of a community is defined by food web interactions. The process of energy flow is the focus of this session as the interactions between producers, consumers, and decomposers are examined.
Session 8 Material Cycles in Ecosystems
Studying an ecosystem involves looking at interactions between living things as well as the nonliving environment that surrounds them. Life depends upon the nonliving world for habitat, as well as energy and materials. In this session, material cycles will be explored as critical processes that sustain life in an ecosystem.