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).
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).
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.
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.
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