[joeyo]

  > This probably happened only once in history and under
  > very specific conditions, which are very unlikely to be
  > repeated.

Anything not forbidden is compulsory. -- Murray Gell-Mann

[ajju]

"Anything not forbidden is compulsory" only if you assume an infinitely long time horizon

Without having more data points, it is hard to say whether the average life span of a planet in the Universe is long enough for multicellular life to inevitably develop.

So far, all evidence points to no. It is also true, however, that so far we have negligible data.