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Recently I have come across this sentence in a biology textbook :

Little more than 15 years after the human genome sequence was announced, researchers had completed the sequencing of thousands of genomes, with tens of thousands in progress.

I have looked at every web page regarding the usage of past perfect tenses I could find, but could not find a single reason why the past perfect tense makes sense in this sentence :

Little more than 15 years after the human genome sequence was announced, researchers had completed the sequencing of thousands of genomes, with tens of thousands in progress.

My understanding of the sentence is that the sequencing of thousands of genomes happened 15 years after the human genome sequence was announced, but the usage of past perfect would mean the exact opposite, at least in my opinion.

I would like someone to shed some light on this sentence and explain why the usage of the past perfect tense is not wrong and what the sentence is supposed to mean. Every answer is greatly appreciated.

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To understand why the past perfect was used here, you need more context than you have given.

Presumably there is some narrative new methods of sequencing genomes that are much faster than the old methods.

I imagine the full context is something like this...

Before CRISPR was invented it took months to sequence a genonme. 15 years after sequencing the human genome, thousands more had been sequenced. But the process was slow. CRISPR made sequencing fast. Individuals could have their own genomes sequenced and oncologists could sequence cancers to fine-tune treatment...

So the paragraph is about the time when CRISPR was invented. By that time (15 years after the human genome project) thousands of genomes had been sequenced. This justifies the use of the past perfect.

Without such context there is no need for the past perfect. It would be grammatical to have used the simple past tense.

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  • Thanks for your answer. I have thought about this context problem myself, but there does not seem to be anything like that in the paragraph where this sentence appears, but that might very well be because I am not a native speaker and I am not getting the deeper connections. This is the only sentence in the entire paragraph that uses past tenses, that is why I was confused. Anyway, your answer that the simple past may be used helps a ton, thanks again!
    – S3th
    Aug 7, 2021 at 10:08
  • Sometimes that can occur because the author has composed a sentence in one way that requires a past perfect, then edited to a form that doesn't require it.
    – James K
    Aug 7, 2021 at 10:23
  • Mhm, I see, that sounds plausible. Thanks for all the help, appreciate it.
    – S3th
    Aug 7, 2021 at 10:39

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