The Selection Pressures 4 is a priority contract to complete for the NuCaloric faction in Marathon, and it’s the final one in the series.
The Selection Pressures 4 quest can be broken down into three separate tasks. Let’s look at how to complete all of them on a single run to finish the Selection Pressures questline.
Table of contents
Marathon Selection Pressures 4 Contract walkthrough
The Selection Pressures 4 contract can be broken down into the following tasks.
- Acquire active contagion sample in Bio-Research
- Analyze the sample using an analyzer in Quarantine
- Download the analysis results, then exfil
How to acquire active contagion sample in Bio-Research

The first task takes you to the Bio-Research POI in the northern part of the map. Get to the second floor using the stairs and reach the end of the walkway (doesn’t matter from which point you enter the walkway).

Reach the building shown in the image above and head inside. Go inside the first room to your left in the building, and the contagion sample will be highlighted for you to scan.
How to analyze the sample using an analyzer in Quarantine

Next, we are headed to the Quarantine in the southwestern part of the map. Go inside the main building, and the analyzer will be located on the second floor inside a room. While the Quarantine is a big area, the analyzer will be highlighted the moment you enter the main building (making it really easy for you to track it down).

You can use the stairs to get to the second floor of the building and then analyze the sample to complete the second task. Place the sample in the inventory for the analyzer, and it will start the analysis. You’ll need to defeat several UESC enemies to unlock the doors.
How to download the analysis results
Kill all the UESC enemies, and interact with the analyzer to download the results. Then, you’ll have to safely exfil from the map. If you die in the process, you’ll need to restart from the first step. Escape unscathed, and you’ll finish the final Selection Pressures contract.