How Many Bacteria Species Can Coexist on a Single Hand? (And do girls really have cooties?)

Sounds like a riddle, but it’s not trivial. We’ll get back to that in a minute. First consider the scenario: The class arrives from physical education. Today’s activity was mat ball, a variation of dodge ball involving lots of kids and lots of contact with balls and mats. They’re pumped, a little sweaty and out of breath, and one or two are a few seconds late—probably not because they were washing their hands! Would you have students wash their hands in this scenario? Not likely. It’s just not part of the lesson plan.

We accept a certain lack of sanitation mostly because it’s not feasible to allow 26-30 kids to wash their hands several times a day. We try to take solace in the hand sanitizers, though rumor has it there’s no substitute for warm water, soap and a minute of scrubbing.

Low-temperature electron micrograph of a cluster of E. coli bacteria, magnified 10,000 times. Each individual bacterium is oblong shaped. Photo by Eric Erbe, digital colorization by Christopher Pooley, both of USDA, ARS, EMU. Wikimedia Commons.

So what’s the big deal? Most bacteria on our skin are harmless or beneficial, right? How many could there be anyway? Well, recently published a story, Women lead men in bacteria types, hands down  that might surprise you. Researchers were surprised to find the incredible number of different bacteria species found among 51 college students’ hands and the very low number of species shared by all students. Further, there was a difference between left and right hands. And finally, there was a significant difference between men and women.

According to the news article,

They [researchers] identified 4,742 species of bacteria overall, only five of which were on every hand . . . The average hand harboured 150 species of bacteria. Not only did individuals have few types of bacteria in common, the left and right hands of the same individual shared only about 17 per cent of the same bacteria types . . .

Researchers suspect differences between left-and right-hand bacteria diversity have to do with each hand’s interactions with environment that can alter the hand’s conditions in terms of oil or salinity, for example. Differences between men and women might have to do with hormone production or slight variations in pH. Researchers commented that, for the subjects involved in this study, hand washing did not appear to remove the bacteria. It is important to note the study did not measure mass of bacteria present or population sizes for each species, only the diversity of species present.

How to Turn This News Event into an Inquiry-Based, Standards-Related Science Lesson

The National Science Education Standards Content Standard F states:

As a result of activities in grades 5-8, all students should develop understanding of

  • Personal health
  • Populations, resources, and environments
  • Natural hazards
  • Risks and benefits
  • Science and technology in society

The ideas in this news article connect to the bullets above. The following discussion highlights the ideas in the list.

Ask students if they’ve ever had a bacterial infection. What caused it? What are bacteria? Many will state they are harmful, disease causing germs. How common do they believe bacteria are? Are they in contact with any right now? How do they protect themselves against bacterial disease? Lead students to understand that many kinds of bacteria are harmless and, in fact, beneficial. Our digestion is aided by bacteria, for example. Bacteria are used in the production of yogurt and cottage cheese, among other foods. You can show them photomicrographs indicating bacteria are distinct cells, but quite small. Bacteria impact our personal health in both positive and negative ways.

How are bacteria connected to populations, resources and environments? Remind students that a group of the same kind of bacteria living in the same area is a population. Can a human hand be an adequate environment with resources to support a bacteria population? How many kinds of bacteria do you think might be able to coexist on a single human hand? Entertain all students’ guesses. Share only the numbers from the story with them. How do their guesses compare with the numbers reported?

Try some true or false questions:

1. There is no difference in the kinds of bacteria found on the same person’s right and left hand.

2. Men and women have the same kinds of bacteria on their hands.

3. Among a group of people, there is a high number of different kinds of bacteria that all people share.

Share the rest of the findings reported in the article. Ask students to generate inferences to account for the variation reported. What questions can they generate related to the findings? What kind of tests do they think would be good to conduct next and why?

You can connect the idea of natural hazards to changes in bacteria populations if you care to. After a flood for example, the biggest threat is disease due to polluted water, from overflow of sewage mixing with drinking-water supplies. At times like these, the bacteria populations found on flood-ravaged persons’ hands can be expected to differ from those found under normal conditions.

What are the risks and benefits involved in controlling bacteria through various methods: sanitation, sterilization, irradiation, and antibiotics, for example? What are the risks and benefits of using helpful bacteria to control or minimize the occurrence of harmful bacteria in food?

What role does technology play in public health policies regarding available vaccinations, medicines, and public education campaigns? See the Centers for Disease Control webpage for additional ideas and information at

To find lessons and activities that would support this topic of study, please search the MSP2 Educational Digital Library – Terms such as germs or bacteria will get you started.

We Want Your Feedback

We want and need your ideas, suggestions, and observations. What would you like to know more about? What questions have your students asked? We invite you to share with us and other readers by posting your comments. Please check back often for our newest posts or download the RSS feed for this blog. Let us know what you think and tell us how we can serve you better. We appreciate your feedback on all of our Middle School Portal 2 publications. You can also email us at

This post was originally written by Mary LeFever and published November 10, 2008 in the Connecting News to the National Science Education Standards blog. The post was updated 2/29/12 by Jessica Fries-Gaither.

Birds of a Feather: Citizen-Science and Data Analysis

Do you need an innovative way to engage students in data collection and analysis? Or maybe you’d like to teach life science concepts in a more authentic context. Whether you are a science teacher, a math teacher, or both, you may want to consider a citizen-science project from the Cornell Lab of Ornithology.

Focusing on bird observation, the projects provide important information about species distribution and behavior to ornithologists. However, much of the data is also accessible online – providing opportunities for students to analyze and conduct inquiry-based projects.

The Cornell Lab of Ornithology sponsors many different citizen-science projects. We’ve highlighted four that might be most appropriate for middle school participation. You can learn more about all the projects at the CLO web site.

Participants record information about bird observations. The database is used by scientists, conservationists, and birdwatchers who want to know more about the distributions and movement patterns of birds across the continent.

Celebrate UrbanBirds
Participants learn about 16 species of urban birds, select a birdwatching area, and observe for 10 minutes, recording which species they see. Scientists use the data to study bird populations, behavior, and their interaction with the urban habitat. Celebrate Urban Birds also includes ideas and resources for urban greening activities.

Project PigeonWatch
Participants observe pigeons and record data about flock numbers, color, and mating behavior. The data is used by scientists to better understand why pigeons continue to exist in so many colors and which colors are preferred for mates. This project does not currently have online data entry available. Printable data forms can be completed and returned to the Lab.

Project NestWatch
Participants monitor nests and breeding habits of any bird species.

A series of BirdSleuth curriculum modules are available for purchase and can help teachers integrate the projects into their classrooms. However, these modules are not necessary for participation in any of the citizen-science projects.

Science and mathematics are seamlessly integrated in these projects. Participating in bird observation allows middle school students to learn these concepts in an authentic setting:

Life Science

·         Diversity and Adaptations of organisms
·         Populations and Ecosystems
·         Bird behavior


·         Data collection
·         Data analysis – graphing, statistics (range, mean, median, mode)

The citizen-science projects from the Cornell Lab of Ornithology can target the Life Science Content Standard of the National Science Education Standards. Bird observations may also lead to student-directed inquiry, which align with the Science as Inquiry Content Standard. Students also work on the NCTM Data Analysis and Probability Standard as well as the NCTM Connections Standard as they apply mathematics outside of a school context.

Best of all, these projects can be completed anytime, anywhere. Get your students outdoors and observing birds today!

We Want Your Feedback
We want and need your ideas, suggestions, and observations. What would you like to know more about? What questions have your students asked? We invite you to share with us and other readers by posting your comments. Please check back often for our newest posts or download the RSS feed for this blog. Let us know what you think and tell us how we can serve you better. We appreciate your feedback on all of our Middle School Portal 2 publications. You can also email us at Post updated 11/28/2011.