One issue that one runs into with your question is how one defines a new field being spun off. Some people have argued that biology didn't really split off from philosophy until the 1850s and 60s, especially with the work of Darwin and Wallace. This is a popular view among Kuhnians who mark a field as becoming science when it gains an overarching accepted paradigm. (However, one could argue that the field left philosophy before it entered science.)
The word "scientist" was first used in 1833, and prior to that "natural philosopher" was used. But certainly by the late 1700s, they were practicing what we could call science. So that argument fails even if one extends the date.
Economics is generally thought of having split off from philosophy when Adam Smith wrote The Wealth of Nations, and that's in the late 18th century. But arguably, merchantilist ideas were a form of economics that predated Smith and were separate from philosophy. And you could push the date farther up, pointing out that until fairly late most of the people thinking about economics are people like Bentham who we think of as philosophers.
Possibly the best example of an area that split off recently might be psychology. Wilhelm Wundt is sometimes regarded as the individual who split that off, doing actual controlled scientific experiments in the late 19th century. But there was research being done by scientists/biologists/natural philosophers much earlier in the 19th century, especially in regards to whether the nervous system was the source of cognition. Wikipedia claims that that work started as early as 1802 with Cabanis (this is surprising to me since I didn't realize he was that early). One could argue given all the subsequent Freudian and Jungian material that psychology didn't really split off from philosophy until that was removed from mainstream psychology which was in the 1960s and 70s. However, that seems like a weak argument.
Linguistics might be another example, but again, how you define the split matters. It also runs into the not tiny issue that much of linguistics spun off from issues of philology, a field already distinct from philosophy. But other areas of linguistics broke off later, and some people still seem to think of issues like Sapir-Whorf as philosophical questions.
So a lot of this seems to depend on definitions, but regardless of definitions it seems clear that no field has spun off in the last 30 years. Going back farther makes the question murkier, but a decent argument can be made that there has been no such spin off in the last 150 years.
I would guess that these splits were generally not recognized as splits until much later when we had distinct bodies of work and then we can look back at the initial roots of the topic. This shows that there might be a bunch of roots of new fields present now that simply haven't grown large enough to be recognized yet.
Creating Friendly AI seems to require us humans to either solve most of the outstanding problems in philosophy, or to solve meta-philosophy (i.e., what is the nature of philosophy, how do we practice it, and how should we program an AI to do it?), and to do that in an amount of time measured in decades. I'm not optimistic about our chances of success, but out of these two approaches, the latter seems slightly easier, or at least less effort has already been spent on it. This post tries to take a small step in that direction, by asking a few questions that I think are worth investigating or keeping in the back of our minds, and generally raising awareness and interest in the topic.
The Unreasonable Effectiveness of Philosophy
It seems like human philosophy is more effective than it has any right to be. Why?
First I'll try to establish that there is a mystery to be solved. It might be surprising so see the words "effective" and "philosophy" together in the same sentence, but I claim that human beings have indeed made a non-negligible amount of philosophical progress. To cite one field that I'm especially familiar with, consider probability and decision theory, where we went from having no concept of probability, to studies involving gambles and expected value, to subjective probability, Bayesian updating, expected utility maximization, and the Turing-machine-based universal prior, to the recent realizations that EU maximization with Bayesian updating and the universal prior are both likely to be wrong or incomplete.
We might have expected that given we are products of evolution, the amount of our philosophical progress would be closer to zero. The reason for low expectations is that evolution is lazy and shortsighted. It couldn't possibly have "known" that we'd eventually need philosophical abilities to solve FAI. What kind of survival or reproductive advantage could these abilities have offered our foraging or farming ancestors?
From the example of utility maximizers, we also know that there are minds in the design space of minds that could be considered highly intelligent, but are incapable of doing philosophy. For example, a Bayesian expected utility maximizer programmed with a TM-based universal prior would not be able to realize that the prior is wrong. Nor would it be able to see that Bayesian updating is the wrong thing to do in some situations.
Why aren't we more like utility maximizers in our ability to do philosophy? I have some ideas for possible answers, but I'm not sure how to tell which is the right one:
As you can see, progress is pretty limited so far, but I think this is at least a useful line of inquiry, a small crack in the problem that's worth trying to exploit. People used to wonder at the unreasonable effectiveness of mathematics in the natural sciences, especially in physics, and I think such wondering eventually contributed to the idea of the mathematical universe: if the world is made of mathematics, then it wouldn't be surprising that mathematics is, to quote Einstein, "appropriate to the objects of reality". I'm hoping that my question might eventually lead to a similar insight.
Objective Philosophical Truths?
Consider again the example of the wrongness of the universal prior and Bayesian updating. Assuming that they are indeed wrong, it seems that the wrongness must be objective truths, or in other words, it's not relative to how the human mind works, or has anything to do with any peculiarities of the human mind. Intuitively it seems obvious that if any other mind, such as a Bayesian expected utility maximizer, is incapable of perceiving the wrongness, that is not evidence of the subjectivity of these philosophical truths, but just evidence of the other mind being defective. But is this intuition correct? How do we tell?
In certain other areas of philosophy, for example ethics, objective truth either does not exist or is much harder to find. To state this in Eliezer's terms, in ethics we find it hard to do better than to identify "morality" with a huge blob of computation which is particular to human minds, but it appears that in decision theory "rationality" isn't similarly dependent on complex details unique to humanity. How to explain this? (Notice that "rationality" and "morality" otherwise share certain commonalities. They are both "ought" questions, and a utility maximizer wouldn't try to answer either of them or be persuaded by any answers we might come up with.)
These questions perhaps offer further entry points to try to attack the larger problem of understanding and mechanizing the process of philosophy. And finally, it seems worth noting that the number of people who have thought seriously about meta-philosophy is probably tiny, so it may be that there is a bunch of low-hanging fruit hiding just around the corner.