[DoctorBeaver (OP)]

Which came first?

Bacteria & viruses are simpler organisms than, say, a dinosaur or a human. So which came first?

If the simpler organisms evolved first, what did they live off of if there were no higher organisms for them to infect? And if the higher organisms developed before bacteria & viruses, why was a seemingly backward evolutionary step to simpler organisms taken?  []

[another_someone]

Bacteria do not need to infect anything.  There are many different types of bacteria, and only some of them are parasites.

Viruses, on the other hand, cannot live independently of other life - thus viruses must be later than bacteria (but both would have predated animals).

This is not to say that evolution does not sometimes simplify things - in some niches, there is no benefit for the complexity, and it can be a liability.

[dkv]

I dont think we can find out which came first.
We assume that simpler the construction carries greater chances of getting created.
Which brings up Virus as the most likely candidate.
Life came out of disease.

[paul.fr]

Bacteria and other single cells organisms, such as prokaryotic cells, came first. This actually relates to a question i have been formulating for about 4 months!

[dkv]

I disagree with the single cell hypothesis.
The truth is there are simpler construction which are 200 to 2000 times smaller than single cell bacteria.
They came first.

[another_someone]

I disagree with the single cell hypothesis.
The truth is there are simpler construction which are 200 to 2000 times smaller than single cell bacteria.
They came first.

There is certainly much speculation on what preceded bacteria, but whatever it was, it could not be what we normally regard as a virus (although there is some speculation that it may have contained RNA, as used by some viruses, before DNA came into use).

[blakestyger]

In reply to another_someone (Viruses cannot live independently of other life).
Neither can animals - they are totally reliant upon plants as they cannot manufacture their own nutrients.

[another_someone]

In reply to another_someone (Viruses cannot live independently of other life).
Neither can animals - they are totally reliant upon plants as they cannot manufacture their own nutrients.

Indeed, but it is not generally questioned that plants and bacteria developed before animals.

In fact, it is not only the issue of nutrients, but free molecular oxygen itself is a requirement for animals life, but from molecular oxygen only exists on this planet as a consequence of photosynthetic life.

As to whether animals actually need plants is open to question, although it is generally assumed that plants pre-date animals; but what is clear is that animals do require some autotrophic life to convert basic raw materials to organic compounds, as well as some photosynthetic life forms; but both these roles can be undertaken by bacteria as well as by plants.