There have been a number of examples, (Why does evolution not make our life longer?, Is evolution a fact?, If evolution is not about increased complexity, why does so much complexity evolve?), where questions that were either considered to be on-topic for the site and were not closed or were closed after several answers had been posted generated many answers that were either unreferenced or were purely based on opinion.
Users who come to this site to look up answers who are unfamiliar with the Stack Exchange model and how the Biology SE community work, may not be aware that there could be problems with an answer that has been upvoted but is not properly referenced. The community needs to have a way to address these types of answers and at the very least be able to add a warning that the answer may lack the necessary facts to be considered a quality answer.
Also, unreferenced answers provide no opportunity for either the OP or someone reading the answer to research deeper, as they would be able to do by reading the source material provided in a properly referenced answer.
Given that we only have two non-moderator users who are active daily that have the 20,000 Reputation needed to propose answer deletions, the community has very little recourse to address poor answers other than with comments or downvotes. The issues are that comments can often be ignored or deleted, and in some cases, an answer may receive a significant number of upvotes, even if it lacks quality, which negates the effect that downvotes should carry.
Currently the only recourse that carries any weight is to raise a moderator flag, which on a mostly good answer that is missing citations is a waste of the moderators' time. Also, unless the question and answers are contentious, people may not think to flag an answer that doesn't provide references, even though it would improve the quality of the answer provided.
At present, moderators have the option of adding the following banner to answers that they feel need to have references and citations.
Some of the information contained in this post requires additional references. Please edit to add citations to reliable sources that support the assertions made here. Unsourced material may be disputed or deleted.
I think that it would be worthwhile to add voting functionality similar to the close vote function for answers, so that the community could put to a vote whether or not an answer is lacking because it has not been properly referenced.
A successful vote would add the banner to the answer, and it could follow the same guidelines for a successful vote as are in place for a close vote.
If an edit is raised to the question, then it would go into a "Remove Banner" queue, similar to the reopen queue, so that if the poster makes an effort to add sufficient references, then the banner can be removed.
If the answer is not fixed after a certain period of time, then it may be worthwhile to move it to a delete queue, or have some form of penalty for not complying with the banner request to add references, such as loss of reputation from all upvotes on the unreferenced answer.
I would also suggest that a disclaimer to the effect of "Unreferenced answers may not be reliable and should be read with caution," should be added to the banner so that those coming to the answer at a later time understands that they need to do more than just read the answer, even if accepted or upvoted, to determine if it is factually correct.