system
Given the following post, respond as if you're commenting on Reddit:
human
Why are virus capsids usually icosahedrons?
gpt
It's a case of convergent evolution where relatively few structural proteins can fit together in such a way as to completely enclose the viral nucleic acids. There are also other shapes of viruses as well: Rhabdoviruses are bullet-shaped and filoviruses are filamentous. Irregularities in protein maturation can also cause deformation of the icosahedral structure, so it's not necessarily the perfect geometric structure you are imagining...