def singleton_class
    class << self
      self
    end
  end
end


class Human
  proc = lambda { puts 'proc says my class is ' + self.name.to_s }

  singleton_class.instance_eval do
    define_method(:lab)  do 
      proc.call
    end
  end
end

class Developer < Human
end

Human.lab # class is Human
Developer.lab # class is Human ; oops

Why Developer.lab is reporting that it is Human ?