I wrote about Ender's Game in an earlier blog because it won two sci-fi literary awards. Ender's Shadow takes place at the same time as Ender's Game, but from the perspective of one of the other children in Battle School - Bean. Besides the difficulties in writing essentially the same story from a totally different viewpoint, Ender's Shadow focuses more on the political ramifications of war and the aftermath that would result from defeating the alien species. Ender's Game and Ender's story itself continues on to describe how Ender deals with his role in the destruction of the Buggers on a psychological and emotional level. Ender's Shadow and Bean's story continues with how Bean uses his super-intelligence to influence the world's politics and establish Earth as one political force instead of multiple individual nations.
On a sci-fi level, Ender's Shadow delves into two main topics: faster than light speed communication (via something they call the ansible) and genetic engineering (specifically whether Bean is still human because he has been genetically altered to be super-intelligent). Orson Scott Card doesn't dig into the science behind either of these ideas - they're sort of just stated as having occurred. Card is more interested in the ethics and consequences of having this technology available. The ansible issues are discussed more in the sequels to Ender's Game. The sequels to Ender's Shadow deal with the physical results of Bean's genetic engineering.
Here's how it's explained in the book:
"Savants were the key, for me. Autistic, usually. They have extraordinary mental powers. Lightning-fast calculations. Phenomenal memories. But they are inept, even retarded in other areas. The human brain could be far smarter than it is. But there is a trade-off. A terrible bargain. To have this great intellect, you have to give up everything else. The genome that allowed a human being to have extraordinary intelligence acted by speeding up many bodily processes. The mind worked faster. The child developed faster.
The key unlocks the mind because the brain never stops growing. But neither does anything else. There is no adult height. There's just height at time of death. You can't keep growing like that forever. There's a reason why evolution builds a stop-clock into the growth control of long-lived bodies. You can't keep growing without some organ giving out, eventually. Usually the heart. The prognosis is 25 years of life."
This is what the sequels to Ender's Shadow address. Bean is a brilliant kid who shapes the politics of the world but he has a severely limited life span because of his altered genes. It's ironic because Bean spent the first ten years of his life super small (all his energy went to developing his brain), and then his body catches up and he ends up a giant. But don't worry! Bean's destiny is not an early death...there are five more books and lots of futuristic science to explore!
