cull the herd
1. Literally, to separate or remove (and usually kill) inferior animals out of a herd so as to reduce numbers or remove undesirable traits from the group as a whole. We had to quickly cull the herd when it came to light that some cows might be carrying an infectious disease.
2. By extension, to separate or remove people from a larger group. With so many people applying for a limited number of jobs, employers have had to cull the herd by introducing much stricter criteria and a more elaborate application for hiring. Universities have long used standardized test results as a means of culling the herd of applicants they receive each year.
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