Dolly the sheep was born on July 5, 1996 and died in February 2003, after she was euthanized following a discovery of a progressive lung disease. Created by the Roslin Institute and biotechnology company PPL Therapeutics near Edinburgh, Scotland, Dolly’s birth was heralded as the first cloning of a mammal, but that was not technically true.
Dolly was indeed the first mammal cloned from an adult somatic cell, as she was carved from the mammary tissue of a fully grown sheep. Cloning in biology is the process of producing genetically identical individuals, or the creation of a copy. By those standards, the first cloned animal was created in 1885.
In 1885, August Weissman produced a theory that he thought would explain why a cell, with all the information to create a human being, could be as highly specialized as a skin cell. He theorized that each daughter cell had half the amount of information as the cell from whence it came, thus diminishing the amount of genetic information.
Capitalizing on this, embryologist William Roux performed an experiment on a two-celled common frog embryo (a blastomere). Since the blastomere was two cells, they would each have the genetic material to create a frog. When he split them apart and destroyed the other cell with a hot needle, the result was half a frog, thus upholding Weissman’s hypothesis.
Hans Adolf Edward Driesch attempted to repeat the experiment with four-celled sea urchins. He shook apart the blastomere. Instead of creating two different half-animals, he ended up with two sea urchins and effectively disproved Weissman’s theory. Driesch recreated the experiment several times with sea urchins, and found the same thing. He came to the conclusion that, in destroying half of the blastomere, Roux had damaged the original cell.
Roux’s and Driesch’s work led to the work of Hans Spemann. Spemann worked with salamanders. Due to their tightly bonded natures, Spemann used his son’s hair as a noose to separate the cells. They created two adult salamanders from the original salamander.
Spemann recreated his experiment, splitting apart the cells of more developed embryos. This time, he created only half-embryos. He determined that, after a period of time in the embryo’s development which he called “determination,” cells became specialized – thus paving the way for modern cell theory.