The Forgotten History of Sleeping in Two Shifts

Zaria Gorvett. The forgotten medieval habit of 'two sleeps'. BBC, January 2022

For much of human history, people didn’t sleep through the night in one long stretch. Instead, they slept in two parts: an early “first sleep,” followed by a quiet period of wakefulness around midnight, and then a second sleep until morning. This pattern was so common that people once referred to it casually in court records, letters, and literature.

Historian Roger Ekirch uncovered this forgotten habit while studying life before the Industrial Revolution. He found that the time between sleeps, often called “the watch,” was used for prayer, conversation, chores, or simply reflection. People didn’t see this midnight waking as a problem; it was a normal part of nightly life.

The two-sleep pattern likely existed because nights were long and dark before artificial lighting. People went to bed earlier and woke naturally in the middle of the night. Modern experiments show that when people live without electric light, their sleep often returns to this older rhythm on its own.

Biphasic sleep began to disappear in the 19th century as gas lamps, electric lights, and factory schedules pushed bedtimes later while mornings stayed the same. Sleep became compressed into a single block, and the old pattern faded from memory. Understanding this history may help explain why waking up at night doesn’t always mean something is wrong. For most of human history, it was simply how people slept.

How Our Neighborhoods Shape Our Health

Noaeen, M., Rostami, A., Ghanem, I. et al. Mapping neighbourhood-level drivers of type 2 diabetes for precision public health using predictive and causal machine learning. Sci Rep, January 2026.

Type 2 diabetes is often discussed as a disease of individual lifestyle (diet, exercise, and genetics). But a new study from the University of Toronto reveals a deeper truth: where you live may be just as important as how you live.

Using artificial intelligence and advanced causal modeling, researchers analyzed data from over 1,100 neighborhoods across the Greater Toronto Area. Instead of focusing on individuals, they examined neighborhood-level features such as obesity rates, physical activity, income, age structure, mental health, and work stress. Their goal was not only to predict where diabetes is most common, but also to understand which factors actually drive that risk.

The results were striking. The AI models were able to identify high-diabetes neighborhoods with more than 95% accuracy. The strongest predictors were familiar – high obesity, physical inactivity, and older populations, but the causal analysis uncovered something more surprising: mental health was one of the most powerful protective factors. Neighborhoods with better average mental well-being had substantially lower diabetes rates, even after accounting for income, age, and lifestyle.

Work stress and smoking, on the other hand, were found to raise diabetes risk, highlighting the biological toll of chronic psychological strain. Interestingly, neighborhoods with higher proportions of recent immigrants and visible minorities tended to have lower diabetes prevalence, reflecting the well-known “healthy immigrant effect” and the protective role of social cohesion and cultural practices.

The study suggests a new vision for public health: instead of treating diabetes only in clinics, we should also treat it in communities, through mental-health support, stress reduction, walkable streets, and social infrastructure. In the age of data science, healing may begin not just with the patient, but with the neighborhood.

The Hidden Effects of Living in Space

Wijdan Al-Ahmadi et al., Spaceflight alters molecular networks linked to diverse human diseases in a single cellular model. Sci Adv, January 2026.

When astronauts return from space, many report strange changes. Their hearts beat differently. Their sleep is disturbed. Their vision becomes blurry. Their muscles weaken. For years, scientists have known about these effects, but not fully understood why they happen. A new study gives us a powerful clue by showing what happens inside human cells when they are exposed to space.

In this study, researchers sent human immune cells to the International Space Station and compared them with the same cells grown on Earth. They then examined how thousands of genes behaved in each environment. Nearly one third of all active genes changed their activity in space. This shows that spaceflight does not just cause small damage. It reshapes the way cells function.

Some of the biggest changes were seen in genes linked to the heart and muscles. These genes help control the electrical signals that keep the heart beating normally. In space, they became much more active. On Earth, the same genes are linked to irregular heartbeats, which may help explain why astronauts sometimes develop heart problems during long missions.

The study also found changes in genes that control sleep and the body clock, including those linked to melatonin. This matches the sleep problems many astronauts experience. Genes involved in vision and other senses were also affected, especially those connected to vitamin A and eyesight, helping explain vision changes in space. At the same time, genes that repair damaged DNA were reduced, likely because of cosmic radiation, making cells more vulnerable to long term damage.

These findings suggest that space activates the same biological pathways that cause heart disease, nerve problems, and aging on Earth, but in a much shorter time. By studying life in orbit, scientists may learn not only how to protect astronauts, but also how to better understand illness here on Earth.