Combine the given two facts to write a concluding fact. Note that there should be some parts of the first and second facts that are not mentioned in this conclusion fact. Your combined fact should be the result of a chain between the two facts. Chains form when two facts connect together to produce a concluding fact. An example of a chain is: "pesticides cause pollution" (fact1) + "pollution can harm animals" (fact2) → "pesticides can harm animals" (conclusion fact). Parts of the concluding fact overlap with the first and the second fact. To construct such a  concluding fact, a useful way is to borrow the subject from one fact and the ending conclusions from another fact.

Fact 1: a glacier causes mechanical weathering. 
Fact 2: Mechanical weathering produces detritus.
A glacier can produce detritus.

Fact 1: Behaviors that improve fitness increase through natural selection. 
Fact 2: Many organism behaviors have evolved through natural selection.
An organism's fitness is a result of evolution.

Fact 1: Some viruses can cause cancer. 
Fact 2: Cancer requires an accumulation of mutations.

Some viruses can cause mutations.