(Left to right): WOLFGANG ADLER, © PHOTO MUSEUM ULM; Ray Bulson/Alamy Stock Photo; ESA/Hubble & NASA

Top stories: The secrets of Roman concrete, superfast stars, and making a pox from mail-order DNA

Neandertals and modern humans started mating early

There’s a new plot twist in the unfolding mystery of how Neandertals were related to modern humans. Researchers sequenced ancient DNA from the mitochondria—tiny energy factories inside cells—from a Neandertal who lived about 100,000 years ago in what is now southwest Germany. They found that the mitochondrial DNA, inherited only from the mother, resembled that of early modern humans. That led to a startling conclusion: A female member of the lineage that gave rise to Homo sapiens in Africa mated with a Neandertal male more than 220,000 years ago—much earlier than other known encounters between the two groups.

Even tiny amounts of oil could doom seabirds

Some of the most devastating pictures after big oil spills are of seabirds coated in black sludge. But a new study reveals that even a small amount of oil could cause major damage to bird populations like the western sandpiper. Just a smudge on their wingtips and tails makes it much harder for them to fly than normal birds, which could prevent them from reaching their breeding grounds in time.

Milky Way’s superfast stars may have been fired out of a nearby galaxy

A small number of stars moving so fast they’ll eventually escape the Milky Way may not have come from our galaxy at all. Until now, scientists have largely believed that such hypervelocity stars originate when binary stars get torn apart by the supermassive black hole at the center of the Milky Way, which consumes one star and flings the other away at incredible speeds. But a new study shows that most of the 20 or so hypervelocity stars found so far might actually come from outside our own galaxy, in the Large Magellanic Cloud, a small satellite galaxy orbiting the Milky Way at nearly 400 kilometers per second.

How Canadian researchers reconstituted an extinct poxvirus for $100,000 using mail-order DNA

Eradicating smallpox, one of the deadliest diseases in history, took humanity decades and cost billions of dollars. Bringing the scourge back would probably take a small scientific team with little specialized knowledge half a year and cost about $100,000. That’s one conclusion from an unusual and as-yet unpublished experiment performed last year by Canadian researchers that synthesized the horsepox virus, a relative of smallpox, from genetic pieces ordered in the mail. Scientifically, the achievement isn't a big surprise. But the new work is raising troubling questions about how terrorists or rogue states could use modern biotechnology.

Why modern mortar crumbles, but Roman concrete lasts millennia

Modern concrete—used in everything from roads to buildings to bridges—can break down in as few as 50 years. But more than a thousand years after the western Roman Empire crumbled to dust, its concrete structures are still standing. Now, scientists have finally figured out why: a special ingredient that makes the cement grow stronger—not weaker—over time. Researchers studied drilled cores of a Roman harbor from Pozzuoli Bay near Naples, Italy. When they analyzed it, they found that the seawater had dissolved components of the volcanic ash, allowing new binding minerals to grow.