sciencehabit (1205606) writes "Cut most species of flatworm in half, and you end up with two flatworms. The front half will grow a new tail and, more impressively, the back half will grow a new head—complete with a fully functioning brain. But a few species of these worms mysteriously lack this ability, at least when it comes to regrowing a head. Now, three teams of researchers have not only zeroed in on the biological reason for this limitation, they've also managed to restore the worms' full regenerative abilities by manipulating a single genetic pathway, reversing a million years of evolution with a single genetic switch."
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