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: Hair helps to insulate and protect the body. 
Fact 2: Hair is composed of the protein keratin.
The protein keratin helps to insulate and protect the body.

Fact 1: gills are used for breathing water by aquatic animals. 
Fact 2: Fish are backboned aquatic animals.
fish use gills for breathing water.

Fact 1: Bottleneck effect occurs when a population suddenly gets much smaller. 
Fact 2: Population growth is reduced by external migration.

Bottleneck effect occurs with external migration.