Spemann splits an embryo.
|In 1902 Hans Spemann, a German embryologist, split a
two celled salamander embryo in two. Following the
division, each cell grew to be an adult salamander,
proving that early embryo cells did indeed carry all the
genetic information needed to create a new organism.
These results disproved Weismann's
1885 hypothesis that the amount of genetic information
carried by a cell diminishes with each division.
Due their tight bonding, Spemann could not shake the cells of the salamander embryos apart as Hans Adolf Edward Dreisch had done earlier in his experiment with sea urchins. Instead, Spemann created a noose from a single strand of his baby son's hair and tightened the noose around the embryo until he split the two cells of the embryo apart.
Spemann repeated the experiment, splitting apart the cells of more developed embryos. Unlike his initial experiment, only half embryos grew from these more highly developed embryo cells. From his findings Spemann concluded that at a certain stage in an embryo's development, which Spemann called determination, the specialization of the cell's of the embryo is determined. According to Spemann's findings, only before this stage can complete organisms can be created from individual embryo cells.