Identical twins arise
when a single fertilized egg (zygote) splits in two. The correct medical term
to describe identical twinning is 'monozygotic'. Fraternal twins are the result
of two eggs fertilized by two separate sperm, hence referred to as 'dizygotic
twins'.
Identical twins have
the same DNA, to a large extent, unlike fraternal twins who are only as
genetically similar as any regular pair of siblings. Thus DNA tests cannot tell
identical twins apart. (However recent studies claim that identical twins can
differ genetically)
Each pair of twins
participating in the study lived in the same environment and ate the same food.
Identical twins participating in the study were genetically identical. Two sets of identical twins and two sets of
fraternal twins and plenty of samples from unrelated children were in the same
room. This was done with the same scientist present so that background odours
would be minimized.
10 German
Shepherds, well trained for identifying suspects by scent were put through
a total of 120 scent line-ups. A canine would sniff a swab and then seek
out a matching scent from seven possibilities. Each dog goes through 12 tests.
Dogs distinguished
identical twins from one another without fail. This was in spite of the fact
that each twin lived in the same place and ate the same food as their
counterpart.
The failure of most of
the previous studies accounted to 'untrained dogs or police dogs that were used
in a variety of capacities, not just for scent line-ups, or very few dogs', say
researchers.
The youngest twins who
participated in the study were only five years old. This meant even people who
have the same DNA and the same surroundings begin to diverge at a very early
age. The exact reason why this happens is unclear. Identical twins, in spite of
having the same DNA have individual smells.
The question 'whether
or when the scents of identical twins start to differentiate with age?' remains
unsolved.
Source: Dogs Discriminate Identical
Twins; LudvikPinc et al; PloS one 2011.
Source: Medindia
