If instincts are passed on through genetics, how is that information encoded in DNA?

For example, spiders instinctively know how to spin webs. Does that imply that the algorithm for web spinning is directly encoded in spider DNA?


Web spinning in spiders is a complex behavior and probably involves a number of different factors, genetic and environmental. Genetically there are surely many different genomic regions underlying the development and expression of the behavior.

Is the algorithm for web spinning directly encoded in the DNA? Not directly. There is not a single region of contiguous DNA sequence that codes for all the steps involved in building a web. Instead, there is a sequential and parallel developmental process beginning at fertilization (earlier if you include parental epigenetic modifications) - encoded and regulated by the genome and its products - that, without too many errors, generates a viable and fertile web-spinning organism. But the DNA sequence involved in that algorithm is spread all over the genome and includes coding genes, non-coding (ncRNA) genes, and regulatory regions. And the genome alone will not carry out an effective algorithm without proper environmental inputs like nutrition and parental provisions.

The act of constructing a web, when and where, and the design of the web is likely carried out via brain architecture and neuronal patterning, but of course these structures are built based on the DNA-based, developmental algorithm. In that sense, there are many nested levels of algorithms.

One of the best models used for studying behavioral genetics is the fruit fly Drosophila. Many different behaviors have been studied at the genetic and molecular level in Drosophila including courtship, foraging, sleeping, and memory-related tasks. A popular science book on behavioral genetics worth checking out is Time, Love, and Memory by Jonathan Weiner. It details the work of Seymour Benzer and provides a lot of background and easily understood explanations of how genes and their products can work together to exhibit complex phenotypes like sleeping patterns. It includes a detailed (though not up-to-date) description of circadian gene circuitry and how it develops.

At the moment, the best that I can think of for an algorithm directly encoded for by DNA is the sequential activation of HOX genes for animal body plans. But even in this case DNA code does not progress through correct development without other factors.

  • $\begingroup$ +1 sound good, do you have any primary references? $\endgroup$ – Abe Mar 7 '13 at 6:31
  • $\begingroup$ Thanks, Abe. If you're looking for some hardcore data, the most interesting paper I've read recently, and that I enjoyed, investigated how innate courtship behavior is modified by learning. Besides characterizing the changes in behavior based on experience, it described the genetics and cell biology that regulates the behavior. nature.com/nature/journal/v489/n7414/full/nature11345.html $\endgroup$ – boloyao Mar 7 '13 at 7:24
  • $\begingroup$ Regarding web-spinning: after a quick search through pubmed, there really isn't much literature on the behavior. The genetics and transgenics of silk production is heavily studied (you may have heard about silk-producing goats), but nothing detailed about web construction. There have been studies on web making by intoxicated spiders. You can find some primary sources from the wikipedia references. en.wikipedia.org/wiki/Effect_of_psychoactive_drugs_on_animals $\endgroup$ – boloyao Mar 7 '13 at 7:41

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