Over decades of research, scientists have built up a partial picture of what specialized cells within the brain and spinal cord do. By studying how the brain develops, they could identify genes that were active in different populations of neurons and where in the brain those neurons resided. In some cases, these genes could then be used to genetically delete the neurons, allowing us to get some indication of what they might be doing, building on the information we've obtained from studies of brains with damaged regions.

But this approach has its limits. The brain is flexible enough to potentially adapt to the loss of some cells, and their loss early in development may alter the development of any neurons they would have normally formed connections with. It would be far more informative to activate and shut down the neurons in an otherwise intact brain.

Today's Nobel Prize in Physiology or Medicine rewards three people—Karl Deisseroth, Peter Hegemann and Georg Nagel—who developed our ability to do precisely that. Starting from studies of single-celled algae that are attracted to light, these and many other researchers built an entire field of study that we now call optogenetics: using light to alter the behavior of nerve cells marked by the activity of individual genes.

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Egyptologists have long debated whether the earliest pharaohs of the First Dynasty were buried with various servants and officials to serve them in the afterlife—a form of human sacrifice. But there is very little archaeological evidence available, given that many of the earliest Egyptian tombs were plundered and/or hastily excavated. A new paper published in the journal Frontiers in Environmental Archaeology reassesses a collection of skulls excavated from tombs in the 1920s and concludes that over one-third show evidence of blunt force trauma. This suggests that they may have been victims of so-called "retainer sacrifice."

Author Roselyn Campbell is a bioarchaeologist at Purdue University who has long been fascinated with the history of human sacrifice. "I'm interested in how we as human beings decide which types of violence are okay and which are not, and how we even define violence," Campbell told Ars. "It's very context-specific. We have to be careful not to extend our own ideas about what violence is and how it's used into other cultures. With Egypt, we have such a long history of European and colonial archeology; they came in with very specific ideas about what this culture was. You really have to make an effort to contextualize the legacy data we have."

Naturally she found the debate over whether ancient Egyptians practiced retainer sacrifice pertinent to her interests. "People tend to fall into one of two camps," said Campbell. "Either retainer sacrifice definitely happened, end of discussion, or it definitely didn't happen, end of discussion. But nobody's actually looked at the bones in a very long time." Forensic science has advanced considerably over the last century, so re-analysis could be useful. Complicating matters is the fact that older sets of remains are often incomplete and/or modified for preservation, destroying vital forensic information in the process.

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