Articles of Interest: What Experts are Saying About Emerging Adult Behavioral Development Since Roper v. Simmons

Thirty years ago this month, the Supreme Court in its land­mark deci­sion Roper v. Simmons found cap­i­tal pun­ish­ment for indi­vid­u­als under 18 years of age uncon­sti­tu­tion­al under the Eighth and Fourteenth Amendments. In explain­ing their deci­sion, the Court drew in part on ​“sci­en­tif­ic and soci­o­log­i­cal” stud­ies show­ing that a lack of matu­ri­ty in youth can lead to ​“impetu­ous and ill-con­sid­ered actions and deci­sions,” which sup­port­ed the idea that this cohort were less cul­pa­ble and there­fore should not be sub­ject to the death penalty. 

The Court in Roper con­fined its rul­ing to 16- and 17-years (it had pre­vi­ous­ly found that youth under the age of 16 were not death eli­gi­ble), but exten­sive research now sug­gests that there is lit­tle dif­fer­ence between the devel­op­men­tal chal­lenges that face ado­les­cents (those under the age of 18) and those fac­ing emerg­ing adults (defined here as 18‑, 19- and 20-year olds) when it comes to impulse con­trol, risk-tak­ing, and the ten­den­cy to bend to peer pres­sure. Here, we share a taste of the research on emerg­ing adult devel­op­ment, which presents a ques­tion sim­i­lar to that addressed by the Supreme Court in Roper, that is, if the emerg­ing adult cohort of 18‑, 19‑, and 20-year olds, whose actions are often both ​“impetu­ous” and ​“ill-con­sid­ered” are actu­al­ly mature enough to be con­sid­ered cul­pa­ble to the degree that would jus­ti­fy their expo­sure to capital punishment? 

Changes in impul­siv­i­ty and sen­sa­tion-seek­ing are present through emerg­ing adult­hood, which could explain dif­fer­ences in risk-tak­ing behav­iors between this age group and adults. A 2011 study by Dr. Paige Harden & Elliot Tucker-Drob exam­ined lev­els of impul­siv­i­ty and sen­sa­tion-seek­ing from the begin­ning of ado­les­cence through emerg­ing adult­hood. The study involved a large sam­ple of 7,640 indi­vid­u­als, between the ages of 12 and 24, who self-report­ed on sur­vey mea­sures of impul­siv­i­ty and sen­sa­tion-seek­ing, both traits influ­enc­ing risk-tak­ing behav­iors. Regarding impul­siv­i­ty, the study found that it declined with age until lev­el­ing off in the mid-20s, which could be explained by neu­ro­science research that has shown the grad­ual mat­u­ra­tion of impulse con­trol areas (i.e. the cog­ni­tive-con­trol sys­tem) through emerg­ing adult­hood into an individual’s mid-20s. Regarding sen­sa­tion-seek­ing, the study found it to increase, until peak­ing around age 16, there­after very slow­ly declin­ing through emerg­ing adult­hood and beyond to the mid-20s. The trend in sen­sa­tion-seek­ing could be explained by neu­ro­science research that has shown brain regions respon­si­ble for emo­tions, nov­el­ty, and reward (i.e. the socioe­mo­tion­al sys­tem) are more sus­cep­ti­ble dur­ing ado­les­cence and emerg­ing adult­hood when com­pared to both chil­dren and adults. According to the authors, this is the first lon­gi­tu­di­nal sur­vey data study to sup­port neu­ro­science find­ings of a dual-sys­tem mod­el of ado­les­cent devel­op­ment com­prised of the sen­si­tive socioe­mo­tion­al sys­tem and the still-matur­ing cognitive-control system. 

In emo­tion­al con­texts, emerg­ing adults, like ado­les­cents, are more like­ly to have issues with self-con­trol and deci­sion-mak­ing. A 2016 study by Dr. Alexandra Cohen and col­leagues com­pared the cog­ni­tive con­trol, includ­ing deci­sion-mak­ing and impulse con­trol, of three age groups (age 13 – 17, age 18 – 21, and age 22 – 25) dur­ing emo­tion­al­ly-arous­ing and non-arous­ing con­di­tions. Relative to adults, both teens and emerg­ing adults demon­strat­ed dimin­ished cog­ni­tive per­for­mance when pre­sent­ed with neg­a­tive cues (i.e. images of fear­ful faces). However, emerg­ing adults did not dif­fer from adults in the non-arous­ing con­di­tion. This sug­gests that the cog­ni­tive con­trol of emerg­ing adults is vul­ner­a­ble to neg­a­tive emo­tion­al influ­ences and marked by con­tin­ued devel­op­ment of the pre­frontal cir­cuit­ry. So, in emo­tion­al sit­u­a­tions, that is sit­u­a­tions that require quick-deci­sion-mak­ing, or ​“hot cog­ni­tion,” emerg­ing adults may per­form poor­ly when com­pared to adults. By way of con­trast, in non-emo­tion­al sit­u­a­tions that allow for thought­ful, delib­er­ate deci­sion-mak­ing, emerg­ing adults may per­form sim­i­lar­ly to adults. 

Emerging adults, like ado­les­cents, are more like­ly to engage in risk-tak­ing behav­ior when sur­round­ed by peers. Studies sup­port the idea that emerg­ing adults are prone to tak­ing greater risks when in a group of same-aged peers. A 2005 study by Dr. Margo Gardner and Laurence Steinberg looked at 306 indi­vid­u­als in three age groups: ado­les­cents (13 – 16), youths (18 – 22), and adults (24 and old­er), to assess the effect of peer influ­ence on risk-tak­ing behav­ior. The study found that while the whole sam­ple engaged in more risk-tak­ing and risky deci­sion-mak­ing, mid­dle and late ado­les­cents (from 13 to 22 years old) were more sus­cep­ti­ble to this peer influ­ence in com­par­i­son with adults 24 and old­er. In one case iden­ti­fied by DPI, five youth were sen­tenced to death in Texas for a group rape/​murder of two teenage girls as part of a gang ini­ti­a­tion. Peter Cantu, Jose Medellin, and Sean Derrick O’Brien were all 18 at the time of the crime and all three were exe­cut­ed. The two remain­ing mem­bers of the group, Raul Villareal and Efrain Perez, had their sen­tences com­mut­ed because they were underage.