[chris37]

That may all be true, but how did the Cvirus gain segments of the HIV virus?

How did it gain spike proteins that unlock two types of human cells while existing in animals?

[Pelham]

That may all be true, but how did the Cvirus gain segments of the HIV virus?

They shared similarities from the start. This is a paper from Sept 2003 right after the first SARS virus burned out. Covid-19 is caused by the SARS-CoV-2 virus.

Cloaked similarity between HIV-1 and SARS-CoV suggests an anti-SARS strategy

How did it gain spike proteins that unlock two types of human cells while existing in animals?

You can read about that here:

The proximal origin of SARS-CoV-2