Re: Ch. 4: The Tree of Life
Yes, I gather that there is a stage in which interbreeding is still possible, but becoming problematic.
It is interesting to think about why humans separated for many thousands of years, especially New World vs. Old World, did not become separate species. Evidently it takes longer than that, although clearly extinction can take less time than that.
Yes and no. It's true that in real time it may take weeks before people's observation of falling sales is confirmed to be economy-wide and they realize it isn't just their business that is affected. But the bit about retrospective identification of recessions refers to a more dramatic issue, and one that does not really match up to the speciation case.
Recessions must be officially identified, because certain laws are triggered when there is a recession on. There are criteria identified by the NBER, which is charged with making the call, but none of them is hard and fast. In 2001, in particular, it was not clear that GDP was falling (before 9/11), which is normally a requirement, but GDP had slowed to barely perceptible growth and unemployment was rising, so the NBER declared (something like six months later) that the recession had begun. (Later data revisions showed GDP had in fact fallen).
It is quite possible that if there had been no 9/11, and the interference with air travel which followed, that the NBER would have read the tea leaves differently and claimed that no recession had happened. That was a hindsight classification, but in theory they are not supposed to base the call on later developments. Usually, of course, it is not such a close call.
When one asks if it is possible for the economy to linger at a tipping point, and have the possibility of going into a recession or not, 2001 is the classic case. But most recessions have reached the point of inevitability by the time the government is aware of them and ready to react. Maybe that is what your comment referred to, but I think that is a phenomenon of delay in receiving information rather than the need to watch dynamic factors play out a little before knowing whether the result is a turn up or down.