Darwin's Flowers

Most people are familiar with Charles Darwin's activities aboard the HMS Beagle and its famous journey to South America. He made some of his most important observations on the Galapagos Islands, where each of the 20 or so islands supported a single subspecies of finch perfectly adapted to feed in its unique environment. But few people know much about Darwin's experiments after he returned to England. Some of them focused on orchids.

As Darwin grew and studied several native orchid species, he realized that the intricate orchid shapes were adaptations that allowed the flowers to attract insects that would then carry pollen to nearby flowers. Each insect was perfectly shaped and designed to pollinate a single type of orchid, much like the beaks of the Galapagos finches were shaped to fill a particular niche. Take the Star of Bethlehem orchid (Angraecum sesquipedale), which stores nectar at the bottom of a tube up to 12 inches (30 centimeters) long. Darwin saw this design and predicted that a "matching" animal existed. Sure enough, in 1903, scientists discovered that the hawk moth sported a long proboscis, or nose, uniquely suited to reach the bottom of the orchid's nectar tube.

Darwin used the data he collected about orchids and their insect pollinators to reinforce his theory of natural selection. He argued that cross-pollination produced orchids more fit to survive than orchids produced by self-pollination, a form of inbreeding that reduces genetic diversity and, ultimately, survivability of a species. And so three years after he first described natural selection in "On the Origin of Species," Darwin bolstered the modern framework of evolution with a few flower experiments.

Student B.

The First Vaccination

Until the stunning global eradication of smallpox in the late 20th century, smallpox posed a serious health problem. In the 18th century, the disease caused by the variola virus killed every tenth child born in Sweden and France. Catching smallpox and surviving the infection was the only known "cure." This led many people to inoculate themselves with fluid and pus from smallpox sores in the hopes of catching a mild case. Unfortunately, many people died from their dangerous self-inoculation attempts.

Edward Jenner, a British physician, set out to study smallpox and to develop a viable treatment. The genesis of his experiments was an observation that dairymaids living in his hometown often became infected with cowpox, a nonlethal disease similar to smallpox. Dairymaids who caught cowpox seemed to be protected from smallpox infection, so in 1796, Jenner decided to see if he could confer immunity to smallpox by infecting someone with cowpox on purpose. That someone was a young boy by the name of James Phipps. Jenner made cuts on Phipps' arms and then inserted some fluid from the cowpox sores of a local dairymaid named Sarah Nelmes. Phipps subsequently contracted cowpox and recovered. Forty-eight days later, Jenner exposed the boy to smallpox, only to find that the boy was immune.

Today, scientists know that cowpox viruses and smallpox viruses are so similar that the body's immune system can't distinguish them. In other words, the antibodies made to fight cowpox viruses will attack and kill smallpox viruses as if they were the same.