Cécile Ané and I talked about problems with comparative methods at #SSB2015 yesterday, from broken methods, to incomplete data, to intrinsically unreachable inferences. One of the unsolvable problems is that we (usually) can’t recognize trends without fossil data — e.g., a clade that has gradually had all its lineages increase in body size through time will end up presenting a facade in extant taxa the same as if the bodies had always been more or less that size. Rich FitzJohn explained it to me with the metaphor of a stream, and in trying to prepare an explanation for our audience, a haiku just popped into my head:
Leaves afloat on stream.
How fast? One glance tells me not.
Please, a second glance!
This led to other haikus. For the problem of pseudoreplication discussed recently by Rich and me, wherein a single clade can be mistakenly interpreted as showing many instances supporting correlation and diversification effects:
Leaves jump, fly, shout
Heed not their many lone cries!
It’s but one wind’s voice.
Our ability to understand diversification is severely hampered by our incomplete picture of phylogeny, with systematic errors in branch lengths from underparameterized models and nearly no information about extinction because of lack of fossils. For this:
Birds know leaves in sun
I know roots and furrowed trunk
Neither knows the tree
Over all, we need to let go of the hope to understand everything about the evolutionary process. There are many interesting problems we can solve, and insights into evolutionary processes we can gain. But, there are also questions we will never be able to answer, either in principle, or because of lack of information.
In youth, I sought it all
Now I know a leaf, and smile
Beauty I can hold
We, as a field, need to look for and find those limits, and come to peace with them.
