It has been said that SARS may be from outer space and arrived at earth on a passing commet. The question here is not about SARS but us. Could we too have arrive on this planet in bacterial form in the same way? Could I be a decendent of E.T.? Most people would say yes to this last question as I dont seem to be like most other people.
Another thing to consider is that if this planet was colonised by bacterial life which we evolved from, might the originators of the bacteria want it back. If this planet has evolved into a habbitable form for the originators then they could want to move in on our nice green turf. To this effect SARS is the answer to thier invasion problem. How do they get rid of the planets dominant species? Well simple they infect us all with a deadly virus and when they arrive the population is reduced and takeover is easy.
Watch the skies people, THEY are comming.