Not sure how they were conceived, but the Morlocks were breeding or cultivating them for food, so they probably were all the same genetically so if one was blonde they all were.
shareWhy are all the people in the future blonde?
Likely thousands of years of artificial selection, the same way our commercially raised turkeys are all white.
Such traits can be refined and concentrated by sexual selection (a collection of physical traits that a culture finds attractive, and selects in favor of) and isolation; think of what it took to produce the dark hair/dark eyes and relatively hairless bodies of Asians and Native Americans. Something like that would have had to have happened to the Eloi at a remote point in their past, either by their own choice, or imposed upon them by the Morlocks.
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