Researchers studying gene expression in mice and fish have just delivered surprising news: Some of the animals’ genes lived on after they died—and others switched on. The authors describe their findings [PDF] on the preprint server bioRxiv. 

Conventional wisdom tells us that when you’re dead, you’re dead. Sure, the microorganisms in your body may go on, but you, as an organism, are kaput. Microbiologist Peter Noble and his colleagues were operating under this basic assumption when they decided to check out the DNA of recently deceased mice and zebrafish. The researchers weren’t looking for anything in particular; rather, they were planning to test a new method they’d developed for measuring gene expression. 

Noble and his colleagues collected tissue samples from the blood and organs of newly departed fish and mice. The researchers then analyzed the animals’ DNA at regular intervals for two days (for the fish) and four days (for the mice), keeping tabs on the activity of 1063 different genes. They expected to find a gradual postmortem shutdown, and for some genes, they did. But 24 hours after death, hundreds of other genes were still kicking, and they kept on kicking right up to the four-day mark.

The story gets weirder. After death, other genes—ones that had lain dormant—actually turned on. Interestingly, most of these “undead” genes are associated with embryonic growth and development, and they typically switch off once an animal is born. At death, apparently, they switch back on. Other members of the zombie gene cohort are associated with tumor growth, a fact that Noble says might explain why people who get organ transplants from newly-dead donors are at a higher risk for cancer. 

The experiments were conducted in lab mice and fish, not people, but the researchers believe their findings have broad implications. As any true-crime podcast fan knows, current techniques for pinpointing time of death are imprecise and spotty. But Noble and his colleagues say that tracking these zombie genes could provide a far more accurate measurement, as they suggest in a second study [PDF] on bioRxiv: "The significance of this study is two-fold: selected groups of upregulated genes provide accurate prediction of postmortem time, and the successfully validated experimental design can now be used to accurately predict postmortem time in cadavers," they write. 

These studies raise all kinds of questions, both scientific and philosophical. The bottom line, Noble told Science, is that “we can probably get a lot of information about life by studying death.”

Know of something you think we should cover? Email us at tips@mentalfloss.com.