What are scientists looking out for as other variants inevitably develop?

Read the following passage. the early mill girls were of different ages. some were not over ten years old; a few were in middle life, but the majority were between the ages of sixteen and twenty-five. the very young girls were called "doffers." they "doffed," or took off, the full bobbins from the spinning frames, and replaced them with empty ones. based on the passage, early mill girls were mostly young. were mostly middle aged. were of a variety of ages. were mostly children.