Can Darwinian Evolution Explain Lamarckism?

If you took a high school biology class, you’re probably familiar with Jean-Baptiste Lamarck’s theory of evolution and its emphasis on the “inheritance of acquired characteristics” — think giraffes stretching their necks longer to reach the leaves high in trees. In textbooks Lamarck’s theory is often presented as a rival to Charles Darwin’s theory of evolution by natural selection. The simplistic storyline is that the two theories battled it out in the 19th century and that Darwinism won, leading to Lamarckism’s demise and the rise of what biologists call the Modern Synthesis.

But recent discoveries have exhibited a remarkably Lamarckian flavor. One example is the CRISPR-Cas system, which enables bacteria to pass information about viruses they have encountered to their offspring. There are also clear-cut examples of transgenerational epigenetic inheritance, in which higher animals affected by environmental factors transmit favorable genetic changes to their offspring across generations. Such mechanisms make sense to us as designers: An animal should pass on, in its genes, information that it has gained about the environment. Such discoveries have sparked debate about the possibility of an update to the Modern Synthesis. Is there a role for Lamarckian mechanisms in modern evolutionary theory?

At the level of specific mechanisms, yes. At a deeper level of causes, though, the answer is a resounding “no” — natural selection reigns supreme. How can that be, you ask? The simplistic juxtaposition of Darwin and Lamarck in elementary biology courses is a false equivalence. If Lamarckian patterns of inheritance do exist, and are indeed beneficial to the organism (that is, they are evolutionary adaptations), then the only way that they could have arisen and been maintained over evolutionary time is by Darwinian natural selection. There’s simply no way around it. Our puzzles for this month explore a simple version of transgenerational epigenetic…

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