Celeste Provo

I understand evolution, and 28 years would give the “infected” a long time to evolve . However, these “infected” were not similar to the 28 weeks later, “infected”. Additionally in 28 weeks later, it was explained the “infected” died after not having a food source. My question is what is the food source for the 28 years later “infected”, animals were shown, however, if the “infected” were using the animals as food sources I highly doubt there would be an abundance of animals 28 years later. The movie was not scary nor a thriller in anyway. It seems 28 years later is a separate entity from the 28 days and 28 weeks story line.