I'm pretty sure its budding, hope it helps
If a species is said to be extinct, then that species is reduced to zero. There are none living in existence. The affects to other organisms of its extinction would depend on their value to the ecosystem. Regardless, extinction completely stops evolution of the species extinct.
Answer:
Testing positive for HIV means a high chance of death and a good chance of lower reproduction rates. But some people are immune to HIV, which makes them more evolutionarily fit, likely to live longer, likely to reproduce more, which would increase the frequency of the immune allele in the population. Over time, this increase in frequency of the gene that causes immunity could spread across the human race and cause it to evolve.