class IntelligentLife    # Wrong way to do this!
  @@home_planet = nil
  def IntelligentLife.home_planet
    @@home_planet
  end
  def IntelligentLife.home_planet=(x)
    @@home_planet = x
  end
  #...
end

class Terran < IntelligentLife
  @@home_planet = "Earth"
  #...
end

class Martian < IntelligentLife
  @@home_planet = "Mars"
  #...
end

