But it did reintroduce that old canard that emotion can only be scientifically studied in humans, specifically: "“We can only know that by verbal report,” he said. “So we can’t scientifically study feelings in any creature but a human.”" I would make two comments to that.
|Max xx / Photo / CC BY-NC-SA|
If we place special value on verbal language-based self-report this is a choice made for reasons other than science, and brings with it the assumption that pre-verbal, non-verbal, or even people speaking other languages may not have real emotions. This exact prejudice that has historically deprived babies and various foreigners the benefit of anesthetics during procedures whether it would be considered inhumane for adult in-group members.
Secondly, if we deem all emotive communications to be essentially similar in their scientific value, which do you really find more convincing, a grammatically correct sentence expressing some kind of suffering... or an anguished scream? I cannot speak to the issue of fruit flies, but I think the days when we felt it at all questionable that other mammals (capable of emotive communication) experienced basic emotions like fear, frustration, or anxiety.
When we consider animals very unlike us such as invertebrates, insects or amoeba, I do not know that the question is really: do they feel fear?--so much as what would fear feel like to them? How morally relevant to us would that experience be? That is the question we will long struggle to answer, and so long as we consider self-report the gold standard of scientific data we will not even begin to make progress towards answering it.