Sixty-six million years ago, an asteroid slammed into the Gulf of Mexico. The catastrophe led to the extinction of as many as three-quarters of all species on Earth, including dinosaurs like Tyrannosaurus rex. But some flying feathered dinosaurs survived, and eventually evolved into the more than 10,000 species of birds living today, including hummingbirds, condors, parrots and owls.

Based on the fossil record, paleontologists have long argued that the asteroid’s impact was followed by a big pulse of bird evolution. The mass extinction of other animals may have eliminated a lot of competition for the birds, giving them the chance to evolve into the remarkable diversity of species that fly around us today.

Continue reading “An Asteroid Wiped Out Dinosaurs. Did It Help Birds Flourish?” →

Women are much more likely than men to have their immune system turn against them, resulting in an array of so-called autoimmune diseases, like lupus and multiple sclerosis. A study published on Thursday offers an explanation rooted in the X chromosome.

The research, published in the journal Cell, suggests that a special set of molecules that act on the extra X chromosome carried by women can sometimes confuse the immune system.

Continue reading “Why Do Women Have More Autoimmune Diseases? Study Points to X Chromosome” →

Multiple sclerosis, an autoimmune disease that affects 2.9 million people, presents a biological puzzle.

Many researchers suspect that the disease is triggered by a virus, known as Epstein-Barr, which causes the immune system to attack the nerves and can leave patients struggling to walk or talk. But the virus can’t be the whole story, since nearly everyone is infected with it at some point in life.

A new study found a possible solution to this paradox in the skeletal remains of a lost tribe of nomads who herded cattle across the steppes of western Asia 5,000 years ago. It turns out that the nomads carried genetic mutations that most likely protected them from pathogens carried by their animals, but that also made their immune systems more sensitive. These genes, the study suggests, made the nomads’ descendants prone to a runaway immune response.

Continue reading “Ancient Skeletons Give Clues to Modern Medical Mysteries” →

Every spring, trillions of flowers mate with the help of bees and other animals. They lure the pollinators to their flowers with flashy colors and nectar. As the animals travel from flower to flower, they take pollen with them, which can fertilize the seeds of other plants.

A new study suggests that humans are quickly altering this annual rite of spring. As toxic pesticides and vanishing habitats have driven down the populations of bees and other pollinators, some flowers have evolved to fertilize their own seeds more often, rather than those of other plants.

Continue reading “Flowers Are Evolving to Have Less Sex” →