Mapping the Future

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Embryo: the egg after fertilization and before it has developed into a recognizable form.

Mechanistic: related to or determined by physical or biological processes. Also, working or acting like a machine.

Prediction: a best guess, an educated guess, about what might happen in the future.

Tolerate: to allow or endure something or someone that is unfavorable. In medical terms, it is a person's ability to take a drug or treatment without serious side effects or discomfort.

Egg Beaters

Part of making a mechanistic prediction involves gathering information about different life stages. But how would you find out if a developing animal is feeling too hot or too cold? If the animal was in a shelled egg, would you knock on its shell and hope for a response? Or would you just assume that it can handle any temperature? Biologists are trying to figure out how to measure what temperatures developing animals can tolerate.

heart monitor

A scientist places a lizard egg in a heart monitor to check the heart rate of the embryo.

Just as human babies have different needs than adults do, the same is true for the needs of baby reptiles or birds, even those still developing in the egg. So how do scientists determine what conditions are good for an animal before it is even born? One way is to record the heart rate of the growing embryo, which is what we call a developing baby before it is born or hatches.

You may have noticed that your heart rate changes if you are nervous or if you get too hot.  The same is true for embryos. For example, an embryo’s heart rate might increase steadily as it is heated up until it reaches 90°F. But at higher temperatures, it could start to slow down. This decrease heart rate tells a scientist that the embryo has become stressed.

heart monitor screen

This screen shows the heart rate of the lizard embryo.

When the egg reaches the temperature that causes its heart rate to drop rapidly, this is called the “breaking point.” By pushing an egg’s heart rate up to the breaking point, scientists are able to determine which temperatures the egg can tolerate. This information helps scientists to develop a more accurate prediction of the types of environments in which babies can survive.

Additional images via Wikimedia Commons. Eggs image by Zack Bittner on flickr.

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Bibliographic details:

  • Article: Egg Beaters
  • Author(s): Adriana Manrique
  • Publisher: Arizona State University School of Life Sciences Ask A Biologist
  • Site name: ASU - Ask A Biologist
  • Date published: June 9, 2012
  • Date accessed: June 27, 2022
  • Link:

APA Style

Adriana Manrique. (2012, June 09). Egg Beaters. ASU - Ask A Biologist. Retrieved June 27, 2022 from

American Psychological Association. For more info, see

Chicago Manual of Style

Adriana Manrique. "Egg Beaters". ASU - Ask A Biologist. 09 June, 2012.

MLA 2017 Style

Adriana Manrique. "Egg Beaters". ASU - Ask A Biologist. 09 Jun 2012. ASU - Ask A Biologist, Web. 27 Jun 2022.

Modern Language Association, 7th Ed. For more info, see
Reptile eggs

Baby reptiles, even those still developing in the egg, have different needs than adults.

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