Science news article:
The article has not been peer reviewed, yet.
What they found was that an ancient transposition event of one ALU
transposon may have started the common ancestor of all apes down a path
to losing their tails.
They found that all the monkeys and apes that they looked at shared one
ALU insertion in the TBXT gene, and all apes had a second ALU transposon
in the gene. Together these two transposons cause miss splicing of the
TBXT gene so you get a shorter defective protein. Human genetic
diseases have been found to be due to transposons inserting into or
around genes. This ancient insertion messed up tail development. They
replicated the same mutation in mice and got messed up tail development
ranging from no tail to shorter tails in mice with the same missing part
of the TBXT protein.
So in the past there was a common ancestor of all extant apes that
suffered the insertion of an ALU transposon into the TBXT gene. It
messed up tail development, and we don't know why the messed up tail
trait was not selected against. It might have been due to drift or some
unknown selective advantage to not having a tail. As I stated before
ALU transposons are still causing trouble and messing up genes in our
current population. This is an example where the ALU mutation did
something that the animal may have found to be advantageous.
The paper doesn't mention it, but other monkeys have lost their tails.
Some Macaques and Mandrills. What would be interesting is that since
Monkeys seem to have the first insertion. The tailless monkeys may have
similar ALU insertions to the second insertion event found in apes. The
insertions don't even have to be in the exact same spot, just be in the
general area so that the aberrant splice junction can form between the
two ALU sequences and remove the exons to make the protein shorter.