LDF Amicus Brief Challenges Racialized ​“Warrior Gene” in Capital Case

On January 20, 2026, the NAACP Legal Defense Fund (LDF) filed an ami­cus brief in the U.S. Supreme Court in sup­port of Amos Wells, a Black man in Texas who was sen­tenced to death in 2016 after a tri­al marked by racial bias and harm­ful stereo­types. The brief urges the Court to grant cer­tio­rari to address the con­tin­u­ing harm caused by the false stereo­type that Black men are inherently violent. 

Central to Mr. Wells’ death sen­tence at tri­al was tes­ti­mo­ny about monoamine oxi­dase A (MAOA), often referred to as the ​“war­rior gene.” The gene codes for the enzyme monoamine oxi­dase A, which plays a key role in the catab­o­lism of neu­ro­trans­mit­ters, includ­ing dopamine, nor­ep­i­neph­rine, and serotonin. 

A defense expert foren­sic psy­chol­o­gist tes­ti­fied that indi­vid­u­als with the low-activ­i­ty MAOA (MAOA‑L) gene, com­bined with adverse child­hood expe­ri­ences and mal­treat­ment, face an increased risk of future vio­lent behav­ior. Because Mr. Wells was found to have both fac­tors, the expert claimed he was 4.5 times more like­ly to engage in vio­lence than some­one without them. 

LDF argues that Mr. Wells’ tri­al reflects a broad­er pat­tern in the U.S. crim­i­nal legal sys­tem, where racial stereo­types about the sup­posed inher­ent crim­i­nal­i­ty of Black peo­ple con­tin­ue to influ­ence sen­tenc­ing deci­sions. In it, LDF draws par­al­lels between Mr. Wells’ case and the land­mark 2017 Supreme Court case Buck v. Davis. In that case, the Court inval­i­dat­ed the death sen­tence of anoth­er Black man from Texas after find­ing his tri­al had been infect­ed with racial bias. “[o]ur law pun­ish­es peo­ple for what they do, not who they are,” wrote Chief Justice John Roberts for the Court, stat­ing that pun­ish­ment based on an immutable char­ac­ter­is­tic ​“vio­lates core prin­ci­ples of justice.”

The LDF brief notes that, rather than serv­ing as mit­i­ga­tion, the tes­ti­mo­ny rein­forced racial stereo­types by sug­gest­ing that Mr. Wells was genet­i­cal­ly pre­dis­posed to vio­lence. The fram­ing of MAOA‑L evi­dence also opened the door for jurors to view Mr. Wells as inher­ent­ly dan­ger­ous, plac­ing race and biol­o­gy at the cen­ter of his trial. 

Research has shown that the pres­ence of foren­sic or med­ical evi­dence in the court­room can heav­i­ly bias jurors. The Fifth Circuit has rec­og­nized that juries are almost always per­suad­ed that a defen­dant is a ​“future dan­ger”– a require­ment for a Texas death sen­tence — when med­ical experts tes­ti­fy. In Mr. Wells’ case, the LDF con­tends this expert’s tes­ti­mo­ny also ensured jurors con­sid­ered future dan­ger­ous­ness through a racialized lens. 

MAOA evi­dence is rel­a­tive­ly new and con­tro­ver­sial. Some courts have refused to accept MAOA-based evi­dence. For exam­ple, in New Mexico, dur­ing Anthony Blas Yepez’s pre­tri­al hear­ing in 2015 on non-cap­i­tal mur­der charges, a defense med­ical expert tes­ti­fied to his MAOA defi­cien­cy and what he char­ac­ter­ized as Mr. Yepez’s “[pre­dis­po­si­tion] to com­mit­ting vio­lent behav­ior.” Prosecutors argued that the tes­ti­mo­ny did not meet pro­fes­sion­al stan­dards for sci­en­tif­ic evi­dence, and the tes­ti­mo­ny was exclud­ed – a deci­sion upheld by the New Mexico Supreme Court. In con­trast, an Arkansas court admit­ted MAOA-based evi­dence dur­ing the sen­tenc­ing phase of Rene Patrick Bourassa Jr.’s cap­i­tal tri­al. He was sen­tenced to life with­out parole. Many legal schol­ars have warned against using MAOA evi­dence in crim­i­nal cas­es, not­ing that while genet­ic mark­ers com­bined with mal­treat­ment may sug­gest risk, they do not ​“cause” criminal violence.