In biology, can one publish results that were already published in a conference proceedings? In my old field (a subdiscipline of computer science) it's not unusual to publish a preliminary version of a paper in a conference proceedings, and then later submit an updated version to a journal, presenting essentially the same result.

My question is, is it possible / accepted to do the same thing in biology? (And theoretical evolutionary biology in particular.)

I ask because some colleagues and I recently developed an evolutionary model that shows some surprising results which are quite relevant to current work in evolutioanry biology. We submitted it to a modelling conference and published it in the proceedings as an 8 page paper. However the feedback I've got from biologists suggests that this result has quite a big potential audience and deserves to be publised in a journal of reasonable impact, where biologists will read it.

To be clear, the journal version would not just be the same text as the conference version - it would be longer, including substantial new analysis as well as more details and context that couldn't be included in the conference version. The question is just whether it's possible (in biology) to present the key result from the model as the main result of the journal paper, or whether the new paper would have to take the form "we present a new analysis of the model previously published in [conference proceedings]". (The latter is possible of course, but I worry that it would limit the impact of the paper, since the new analysis is a much more incremental advance.)
Yes I believe this is possible, but depends on the policies of the specific journal and the nature of the conference publication.

Actually I know of cases where journal editors contact authors of work published in conference proceedings, and suggest submission of an extended version in their journal. This would typically happen in a relevant sub-field where both journal and conference publications are possible, such as bioinformatics.