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Inherit the Stars - First Contact, by Yukinobu Hoshino, Grade: B
Not a lot more to add regarding my opinion of the manga. The artwork is still good, although the character faces are occasionally messed up. The narration is still too wordy and doesn't add that much to the story. And I have a few complaints about the "science" part of the SF.
(Danchekker describes what he's been able to figure out about the Giants' physiology.)
The story: Shortly after Hunt and the others learn about the Giants, they reconstruct what they think happened. The Giants lived on Minerva, but the CO2 levels were rising and they built space ships a few million years ago to explore other worlds where they could live. They tried moving to Earth, but the CO2 levels were already too high and the planet was too cold. Instead, they just collected samples of the Earth species, including a Cro-Magnon Man. This guy figured out how to escape the cage, saw the Giants controlling the ship, and tried duplicating their actions to get back to Earth, managing to crash the ship on Ganymede and killing everyone on board instead. Meanwhile, a different Giant ship traveled to another star to try to rebalance it to make that system livable, and again, they screwed up and blew up the star, destroying their hyperdrive. The crew of the ship used their orbit around the star to reach near-light speed before sling shooting back home just in time to intercept the beacon that Hunt and crew turn on. The Giants visit Hunt and the other humans, and everyone becomes friends.
(First contact with the surviving Giants.)
One part of the speculation has the surviving Minervans leaving the moon and going down to Earth, where they turned into Homo Sapiens and wiped out the pre-existing Neanderthals 50,000 years ago. It seems, though it hasn't been explained yet, that the Jevlen "Peace Council" might have been from the other side of the Minervan conflict, and they've been on Earth trying to get the humans to kill themselves off, while stockpiling weapons and slowing down human technological advances. Both WW II and the Cold War were instigated by the Jevlen. Currently, the Jevlen claim to be enforcing the peace, as a cover for hiding information on the Giants. When the Jevlen learn that humans have made contact with the Giants, they go into a panic and begin work on wiping out the humans once and for all. Meanwhile, Danchekker and a couple assistants do some DNA analysis on the tissue samples they've managed to amass. They have a lab rat running a maze to find the cheese, then inject that rat's DNA into other rats to show that the transferred DNA allows the other rats to run the maze faster, too. But, the injected rats turn violent and attack each other rather than share the cheese. Hypothesis - human intelligence is the result of failed DNA manipulation by the Giants, as is the human tendency towards violence. The book ends with the Giants making their first visit to Earth, where they are greeted by the humans as friends.
One note on the title: The original English title was "The Gentle Giants of Ganymede". The Japanese title of the wide books is "ファースト コンタクト" (First Contact).