However, even though a population of Always Cooperate and Tit-for-Tat can coexist, if there is a small percentage of the population that is Always Defect, the selective pressure is against Always Cooperate, and in favour of Tit-for-Tat.
Namun, walaupun populasi dari Selalu Kooperasi dan Tit-for-Tat dapat bekerjasama, jika ada sejumlah kecil persentase populasi yang Selalu Bertahan, tekanan selektifnya adalah melawan Selalu Kooperasi, dan mendukung Tit-for-Tat.