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Francis Collins, left, and Craig Venter led rival teams that raced to decipher the sequence of chemical components in human DNA, the master molecule of heredity. Their success is the first step toward gaining the power to tailor our genes, which could revolutionize medicine but may also tempt us to try to improve on nature.

Few diseases are more terrifying than the slow descent into dementia known as Alzheimer's. But this year researchers made excellent progress in finding errant genes that contribute to the condition. They also began to test compounds that attack beta amyloid, a protein that may cause Alzheimer's by clogging brain cells. If that theory proves true, the first effective therapies may be on the way.

The five cloned piglets presented to the world by PPL Therapeutics, a biotech firm with offices in Scotland, New Zealand and the U.S., were not as cute as Dolly the lamb. But they could be far more important. PPL is using genetic engineering to develop a breed of pigs whose organs can be successfully transplanted into humans. If it works, cloning could someday provide a hefty supply of organ donors.

In the Mediterranean Sea off Alexandria, French underwater explorer Franck Goddio found Herakleion, the long-lost Egyptian port city described in classical writings. Herodotus visited the city in 450 B.C. and saw a temple honoring the fabled Hercules. Among the treasures Goddio recovered were a basalt head of a pharaoh, a life-size, headless statue of the goddess Isis and a bust, above, of Serapis, the bearded sun god.

Mars once had oceans and rivers, much like Earth, but ages ago the Red Planet dried up totally-or so most scientists thought until this year. New images from the Mars Global Surveyor show channels on the surface that could have been made recently by water flowing from underground sources. The discovery increases the probability that some form of life lurks in the planet's inner recesses.

Even a mammogram may not detect a breast tumor until it has been growing for five to seven years. That's why researchers worked this year to develop methods for uncovering tinier tumors. Three of the strategies have shown promise: blood tests to detect the cancerous cells shed by tumors, the removal of fluid from milk ducts in the breast to check for cells that show abnormal growth and the use of magnetic resonance imaging to find trouble spots.

The furry, four-legged creature, which lived 45 million years ago, could fit into your hand. Yet Eosimias, new evidence shows, was a link in human evolution: the oldest known higher primate, a group that gave rise to monkeys, apes, Democrats and Republicans.

Studies have shown that drinking black tea lowers your risk of suffering heart disease or a stroke. Now new research offers an explanation for this benefit. Black tea may help blood vessels that have loose elasticity by restoring the vessels' ability to expand when the pulse rate quickens. So that morning jog is less likely to give you a heart attack.

In 1864, during the American Civil War, the Confederate submarine H.L. Hunley torpedoed and sank a Union ship off South Carolina. Then, for unknown reasons, the Hunley went to the bottom of the Atlantic. There it lay until this year, when a team led by U.S. Navy archaeologist Robert Neyland raised the Hunley in hopes of solving the 136-year mystery of its sinking.

After the French Revolution, Louis XVII died of tuberculosis in a Paris prison at age 10. Or did he? In the following decades dozens of people claimed to be the real dauphin. They were not proved to be imposters until this year, when scientists matched dna taken from the imprisoned boy's mummified heart with samples taken from preserved locks of the hair of his mother, Marie Antoinette. Case closed.