All of us are left-handed. At least, the bits that make up our
proteins are. This is surprising since Nature is predominantly
ambidextrous when it comes to assembling these molecules from
scratch. Some scientists argue that left-handedness was handed
down to us from space, but others say it just happened by chance
in some little nook on the primordial Earth. Amino acids, sugars
and other chiral molecules come in two varieties that are mirror
images of each other. Handedness, or as it's technically called,
"chirality," occurs in certain molecules that come in two
varieties that are mirror images of each other, like right- and
left-handed gloves. In living creatures, amino acids – the
building blocks of proteins – are almost exclusively left-
handed. Whereas, the sugars that make up the helical backbone of
DNA and RNA are all right-handed. (Scientists tend to focus on
the left-handed amino acids because they are easier to analyze
than the right-handed sugars.) Life's exclusive use of one hand
over the other is r