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Comment by iamleppert | Hacker News Reader

Isn’t it obvious they aren’t physically identical? They have the same genes but are not identical!

The term is being used in reference to their genes, not their appearance.

I'll mirror what someone else said, have they actually sequenced them? Clearly a lot of changes happened at a very early state, mutations, so why should we expect their genetic makeup to be identical?

Also:

In animals and human chimeras, this means an individual derived from two or more zygotes, which can include possessing blood cells of different blood types, and subtle variations in form (phenotype).

https://en.wikipedia.org/wiki/Chimera_(genetics)

For example, in 2002, news outlets reported the story of a woman named Karen Keegan, who needed a kidney transplant and underwent genetic testing along with her family, to see if a family member could donate one to her. But the tests suggested that genetically, Keegan could not be the mother of her sons. The mystery was solved when doctors discovered that Keegan was a chimera—she had a different set of DNA in her blood cells compared to the other tissues in her body.

https://www.scientificamerican.com/article/3-human-chimeras-...

it’s almost certainly not identical now, it just used to be at conception

"Identical twins" is not a description of the twins character, specific physical features, behaviour, nurturing. Instead, 'identical twins' is a noun-phrase meaning two children from a single zygote, ie 'monozygotic'.

It does not mean "twins who are literally identical"; though you could think of it as twins who are genetically indistinct.

I'm a physicist with no biology qualifications, but it just sounded to me like you may have misunderstood the linguistic meaning. Apologies if I was wrong about that.

This is where English terms we use is very imprecise and can be confusing. English calls twins that were once the same zygote "identical" no matter what they look like or what happened after the zygote split.

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