|MadSci Network: Genetics|
Interesting questions! Unfortunately, I can't find any specific information on either beavers or spiders. I have found a general statement (which lists as examples both beaver dams and spider webs) suggesting that construction behavior is usually innate, although construction abilities can improve with learning. And that leads me to my main point: most if not all behaviors involve both genetic and environmental components. A beaver that has never seen another beaver might be able to build a dam, but it might not do it--it might go searching for other beavers instead. Alternatively, beavers might be genetically pre-disposed to build dams, but they may need prior experience with a dam or need other dam-builders around in order for them to actually build a dam. This means that it is very difficult to figure out the relative importance of genetic and environmental influences. As a result, most people are tempted to view the issue as black or white: genetics OR environment (nature OR nurture). When you start talking about humans, there are all sorts of political reasons to choose one OR the other of these answers, and that makes the discussion even harder (but I'm not about to get into that debate!!)
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