Scientists have traced the ancestry of the modern horse to a lineage that emerged 4,200 years ago and quickly became dominant across Eurasia. The research published Thursday suggests that's when humans started to spread domesticated horses around the world. This horse lineage had a genetic mutation that changed the shape of its back, likely making it easier to ride. People had domesticated other animals several thousand years before horses — including dogs, pigs, cattle, goats and sheep. But the new research that analyzed 475 ancient horse genomes shows that the shrinking genetic diversity associated with domestication happened much faster in horses.

For the first time, researchers have identified a genetic form of late-in-life Alzheimer's disease. Most cases of the mind-robbing disease occur after age 65. A gene called APOE4 has long been considered a key risk factor. But new research says if people inherit two copies of that gene it's not just a risk — it appears to be the underlying cause. About 15% of Alzheimer's patients are thought to carry the gene pair. Scientists say the distinction could have implications for both research and treatment. The findings were published Monday in Nature Medicine.

The coffee that picked you up this morning is 600,000 years old. Researchers have found that the world's most popular type of coffee, known as arabica, emerged hundreds of thousands of years ago through natural crossbreeding of two other coffee species. Using genes from coffee plants around the world, scientists built a coffee plant family tree to better understand where it came from and how to better protect it from disease and climate change. These wild coffee plants originated in Ethiopia but are thought to have been first roasted and brewed primarily in Yemen starting in the 1400s. The research was published Monday in the journal Nature Genetics.