Did you predict that in each interaction there would be an evolutionary pressure to reduce negative effects or increase positive effects? those predictions make sense, but why, after 3.5 billion years of evolution, do we still have interactions with negative effects?

Yes, in each interaction, there would be an evolutionary pressure with negative and positive effects

Explanation:

Parasitism and mutualism are two fundamental relationships in evolutionary studies with negative and positive effects respectively. Even after 3.5 billion years of evolution, we still have some form of parasitism among animal species that result in negative effects. This may be due to the necessity of evolutionary interactions and the balance maintained by ecological nature for both fauna and flora. Individual species compete for the limited resources available for ultimate survival. In mutualistic units with two species, there must be a parasitic character.

since there isn't any suggested answers i will give you the reason and hopefully you can figure it

south africa, or rather all of africa, has not been in the location in which it is nowadays throughout the geological past. after the super-continent pangaea started to break apart, gondwanaland, in which was africa, moved further south, and parts of it came to be very close to the south pole. because the climate in this part of the world is very cold due to the very dispersed sun rays in there, what is now south africa, started to freeze, and the conditions were right for the formation of glaciers. the glaciers existed up until the period when gondwanaland started to break apart and what is now africa started to move towards north, sp it warmed up and the glaciers melted.