I’m wondering if you can tell me: what makes a hair stop growing? Why do, say, leg hairs or eyebrows stop growing,
but the hair on my head continues to grow?
Thank you for your question regarding differential growth rates of human hair types.
This is a very interesting question that has been addressed recently in a scholarly article – Human Head Hair Is Not Fur by AH Neufeld and GD Conroy. Evolutionary Anthropology, vol. 13:3, p. 89, June 2004.
Humans, like other mammals, have hair over most of their bodies. Head hair is different from hair elsewhere on the body because it continues to grow (although it is anatomically the same as other hair). When head hair is transplanted elsewhere, it grows longer than the hair on those parts of the body.
Here is a description of the growth process from that article:
“Both head hair and body fur grow in cycles. The hair follicle produces a strand of hair during its active growth phase, called anagen. Then the growth slows, and the follicle “rests” for a while, the telogen phase. Then comes exogen when the hair falls out, and the follicle begins growing a new strand of hair as the anagen phase begins again. Hair on the leg usually grows for 19 to 26 weeks and then falls out. Hair on the head keeps growing for two to six years.”
The article states that it is not known why head hair continues to grow, and further research is needed.
We hope this information is useful.
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Gale Science in Context (formerly The Science Resource Center) is a one-stop science database for all your science-related research needs. This in-depth, curriculum-oriented, resource focuses on key concepts taught in school classrooms, including…
- Earth and Environmental Science
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In addition to these six major subjects, the revamped database main page provides access to approximately 390 preselected topics ranging from “abortion and family planning” to “zoology.” It also presents more complex topics such as “reflection, refraction, diffraction and wave interference.” Searchable content includes images, academic journals, experiments, news, magazines, statistics, videos, audio plugs and websites.
Choose the topic “evolution” and you Continue reading “Science Insight – Science Databases”
The reference librarians at The Seattle Public Library are pretty darn amazing. They don’t know everything, instead they know where to find everything. As part of an irregular series of posts we salute the talented and dedicated reference staff at your local library. Names and other identifying information have been removed from the questions we showcase. Got a stumper? Click on Ask a Librarian. It’s what we do.
“What part of the brain controls writing (forming letters)? “
We have found some good basic information on the website of the Center for Neuro Skills. This site describes the parietal lobe near the back and top of the head as having the functions Continue reading “June Question of the Month – An irregular series”