When Darwin was building the case for his Origin of Species, he
frequently relied on breeding of domestic animals as an example.
If people could create so many varieties by selectively breeding
naturally occurring variations, just imagine what natural
selection could do over deep time, he argued. Now, researchers
have identified a single mutation that changes the way horses
can manage their gait, or the timing and pattern of their leg
movements. Although the mutation shows up in a number of breeds,
it's present in a very high number of harness-racing
trotters—where its presence was linked to increased winnings.
Horses are noted for having a variety of very distinct gaits,
ranging from ambling and trotting, up to a gallop. Each of these
comes with distinct rhythm of leg movements, placement of
footfalls, and patterns of fore- and hind-limb motions. As
horses have been bred for everything from heavy lifting to
showing off in flashy parades, different gaits have become
predominant in specific breeds. The new wor