library_construction_protocol: Sperm was isolated from semen (which contains various cell types) using a published discontinuous gradient protocol (Wu, de Gannes, Luchetti, & Richard Pilsner, 2015). DNA was isolated from the purified sperm cells using a Qiagen AllPrep DNA/RNA mini kit following the manufacturer's protocol. Somatic cell contamination after sperm isolation never exceeded 1% of total cells. The samples were sent to Admera Health (South Plainfield, NJ), a CLIA-certified laboratory, for WGBS analyses. The directional Illumina TruSeq DNA Methylation library kit was used for sample preparation following the manufacturer's protocol. WGBS was then performed on an Illumina HiSeq X sequencer resulting in 150 bp PE reads achieving roughly 4x coverage genome wide per sample. Raw FASTQ files were received from Admera Health for further analyses. All samples were processed blindly without the processors' knowledge of tertile level from sperm isolation through the WGBS analyses.