Rohan Maddamsetti
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The price of a Metaphor is eternal vigilance

3/1/2016

1 Comment

 
Humans naturally use metaphors and analogy to reason about the world. Analogies help people see connections between disparate fields, and they help people generalize and make abstractions. Darwin’s key insight was that evolutionary change in the natural world could occur through processes similar to animal breeding or plant domestication—“natural” selection is like artificial selection. Analogy is even useful in fields as abstract and precise as mathematics (see chapter 6 of this very useful book). For example, a function takes a number as input, and produce a number as output. Operators (such as differentiation in calculus) are analogous to functions: they take a function as input and produce a function as output.

​The danger occurs when analogies break down and become positively misleading. I learned last week that one of the problems that many students have in learning about evolution, is understanding that mutation is a random process of change. Mutations don’t occur in a directed fashion when they are needed. My thinking is that this false lead comes from an easy, but false analogy between evolution and learning.
 
People can adapt to new circumstances through learning, and learning is usually driven by some need or desire to change. Evolution can produce outcomes that look like they were produced by learning: the classic example is the false Lamarckian belief that giraffes could evolve longer necks through a process of successive generations of straining for higher and higher branches of a tree. It’s true that “use it or lose it” applies to how people learn. But is the same true of evolution? Did giraffes evolve by “learning” to reach higher and higher branches?

A lot of productive science occurs when people think deeply about common assumptions or analogies that seem true on first glance but are actually false. Salvador Luria was obsessed by the question of whether mutation was random or directed, and developed a key experiment with Max Delbruck that resolved the question. Luria and Delbruck proposed that if mutations occur in response to need, antibiotic-resistant mutants should occur in response to antibiotic treatment. If antibiotic-resistant mutants arise randomly, but then preferentially survive antibiotic treatment, a particular “jackpot” distribution of mutations would occur. Here is a schematic of their experiment (Luria and Debruck 1943).
Picture
If antibiotic-resistant bacteria arise in response to antibiotics (picture A), then it's reasonable to assume that similar numbers of mutants will arise in replicate experiments. If antibiotic resistance occurs as a result of a random mutation however (picture B), then the number of resistant mutants will vary dramatically depending on when the mutation occurs. If the mutation occurs very early in the experiment, then a "jackpot" of resistant mutants will appear in the end. Also notice how 'jackpot' is an analogy that helps us understand the experiment!

​By figuring out that evolution is NOT like learning—mutations are random—Luria and Delbruck won the Nobel prize. So—while analogies are generally a good mental tool, understanding when and how they break down is very, very important.
1 Comment
Boris Borcic
7/9/2017 12:58:48 am

Landing here while searching google on the quote in your title. I think you miss the cause of the students being misled. Ask Google images for "evolution". There it is. Repeated countless times. Unless you read off this traditional representation, with time running left to right, as implying (the equivalent to) an individual being who is transforming as he goes forth -- the misconception of your topic -- what you get is a sequence of species with our own leading the way, which is the opposite of what really happens -- the ancestor species preceded us, we trail, which is why we can see their traces. To be accurate instead of misleading, the picture thus would need to independently mirror each figure in the sequence left-right. The latter is the charge I've repeated against that representation, context prompting, like a dozen time over decades. The former is a conclusion I reached a few day back, the last time, just a few days back, because in the end I found the explanation I'd given myself of the universal preference for this wrong version -- people convening of the superiority of man over other species, represented by the leading position -- inadequate, insufficient. So I asked myself what I was missing, what do people read into that representation that I am missing -- in particular, the kids that perforce shouldn't read it as a representation of the superiority of man, since - given the famous "controversy" - a thing they know beforehand is that evolution theory dethrones man from the master position that creationism confers to him.

A fun angle is that the wrong wisdom convened by this representation, by the way it neglects its natural meaning from the viewpoint of kids, shares nature with the wrong wisdom about Genesis 2-3, "the original sin", conveyed by the folk wisdom that the exact name of the forbidden fruit, eg "knowledge of good and evil", is really a fig leaf. There you'd have an hypocrite God convening of a fig leaf with the adult reader, in a story whose clearest element in the eye of a kid, is that seeing fig leaves enrages Him.

Last point, the maleness -- writing this it felt awkward that I needed to rely on the male gender to refer to the figures in the picture, for the sake of not complicating my language -- this opens the question whether the right way to rectify that loathed traditional picture of evolution, should not be to transform the figures from male to female, simultaneously to making them face left instead of right, towards the past. That's just a question to ponder, since at first blush that tweak seems likely enough to be misinterpreted in turn.

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    I am a postdoc at Harvard Systems Biology. Views here are wholly my own, and reflect my thoughts at the time of writing.

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