Because biological processes can result in different loci having different evolutionary histories. species tree estimation requires multiple loci from across multiple genomes. While many processes can result in discord between gene trees and species trees. incomplete lineage sorting (ILS). https://www.hindigyanvishv.com/best-catch-Sunjoy-9-x-11-Foot-Arched-Pergola-Cover-Backyard-Roof-Canopy-Tent-For-Parts-p29332-mega-find/