In I Am Legend by Richard Matheson, what does this mean?

The rest of her letter wasn’t a lie, he knew that. Without the pill, without any evidence of word or memory, he knew. He knew what even Ruth and her people didn’t seem to know.

He looked into the eyepiece for a long time. Yes, he knew. And the admission of what he saw changed his entire world. How stupid and ineffective he felt for never having foreseen it!

Especially after reading the phrase a hundred, a thousand times. But then he ’d never really appreciated it. Such a short phrase it was, but meaning so much.

Bacteria can mutate.

Why did Neville say that? Did he mean that the newly formed Society will itself fall to death due to the mutation?

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    I don't remember this being the ending. I remember another scene after this with him in prison waiting for his execution and among the last lines were his thought that he is now the monster of legends. Are there different versions of this story?
    – slebetman
    Commented Jan 14, 2022 at 23:26
  • @slebetman - i checked, it is not the end at all but Chapter 18, the end you speak of is in Chapter 21. Commented Jan 16, 2022 at 15:54

1 Answer 1


The operative part of the quote is "Bacteria can mutate," which is shorthand for the idea that living things can change. The point is both that the original disease that killed so many and made the rest "vampires" is changing, and so are the infected people changing, as the bacteria and its hosts (humans) adapt to one another. (Note also that Neville is changing too, with the knowledge he has just received.)

You need to consider this in the context of what has just gone before. Neville made a slide of Ruth's blood and discovered that she was infected:

"Yes, but—" He broke off as he slid the glass slide onto the microscope.

"Robert, what could you do?"

She slid off the stool as he bent over the microscope.

"Robert, don't look!" she begged suddenly, her voice pleading.

But he'd already seen.

At which point she attacks him, since she's afraid of what he will do to her. (Up to this point Neville has killed every infected person he's found.) When he wakes up, Ruth is gone and he finds her letter.

The letter tells him that the infected have learned to live without always needing fresh blood. They have stopped preying on one another, and the living infected are wiping out the undead infected; in fact the living infected are forming a new society.

What you don't understand yet is that we're going to stay alive. We've found a way to do that and we're going to set up society again slowly but surely.

Neville then simply picks up the microscope:

Then he looked up. Slowly he slid off the stool and placed the microscope back on its base.

He doesn't prepare a new slide, he's still just looking at Ruth's blood. And what he sees simply confirms what he saw before she hit him - she's fully infected. That realization means that a fully infected person can be a person; can laugh, care, and be fully human. (It also means that some of the infected he's been executing were people; that he has been murdering people.)

What Neville had never foreseen, and what nobody else seems to have realized yet, is that diseases and hosts can reach a biological accommodation that allows both to survive. What "Ruth and her people" don't know is that they are not a new people starting their society; they are just human people, slightly changed, trying to put society back together. Bacteria can mutate.

  • He is looking at the bacteria through a microscope (hence 'eyepiece') and can see with his ow eyes that it they have mutated. He can't, of course, see the DNA itself, but the mutated bacteria may have a different pattern of outgrowths. Commented Jan 14, 2022 at 12:02
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    @KlausÆ.Mogensen He's just picked the microscope up off the floor; he hasn't set anything new up in it. The last thing he prepared, before Ruth's attack knocked the microscope (and him) over was a slide of her blood. Neville is looking at Ruth's blood and seeing the bacillus and realizing that an infected person can still be a person. It's not that the bacteria has changed, he can't see that, it's his understanding.
    – DavidW
    Commented Jan 14, 2022 at 14:26
  • @DavidW The passage you quote appears to describe him having “bent over the microscope” and “already seen” before Ruth knocks it over. But it does also work if what he’d seen were her actions, instead of the slide.
    – Davislor
    Commented Jan 14, 2022 at 23:25
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    @Kashmiri No. The bacteria didn't affect Neville because, before the global plague, he had been bitten by an infected vampire bat that gave him a weakened form of the bacteria; he was able to survive (though he got very sick). When the plague came he was immune.
    – DavidW
    Commented Jan 15, 2022 at 4:29
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    @StanleyWebb: This sinister idea occurred to me also when reading the line: that their efforts to rebuild might be futile. However, in real life two medieval plagues, syphilis and bubonic plague both lessened in severity. I don't know if science understands why this happens although it can help illnesses/bacteria spread better since the infected don't die as fast and if outward signs are slower to appear, other humans are more likely to interact with them -- maybe that simple: bacteria that produce fewer outward signs are preferentially chosen for.
    – releseabe
    Commented Dec 7, 2022 at 8:06

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