Вот здесь можно прочитать, кто "повинен" и с какого времени, в появлении (или развитии, если точнее) секции "мамбо" в бачате. Первоисточник -
http://iasorecords.com/artists/antony-santos.
While modern bachata does not begin with Santos, the innovations which he and his group introduced into the genre have been extremely important in defining its current form. Previously, lead guitarists like Edilio Paredes and Augusto Santos played upward with their fingers in a florid, melodic style; even Jesús Martinez, Blas Durán’s pioneering lead guitarist, used his fingers to play although in a simpler fashion. Antony Santos, followed the lead of his mentor Luis Vargas and of Eladio Romero Santos in playing the strings downward, with a thumb pick. The resulting style was simpler and more rhythmic, and has given bachata an instantly recognizable sound when compared with other kinds of Latin guitar music. Meanwhile, the bachata which Santos was recording began to reflect, more and more, the influence of his merengues. His bongo player played the instrument with two sticks, rather than with his hands, and many of the breaks had a merengue feel. In addition, the group developed a mambo section in which the güira plays a pattern typical of merengue and the bass plays a pattern derived from the cha-cha-cha section of traditional bolero. In the merengues themselves, the traditional tambora rhythm was replaced by a simplified version of “caballito”, the rhythm made popular by merengue orquestas like Los Hermanos Rosarios.
As the decade of the 1990s went on, Santos was consistently successful with both his bachatas and his merengues, and the rhythmic patterns which his group developed for the different sections of the song came to be the standard for the genre.
Если перевести в двух словах, то секция "мамбо" пришла в бачату с творчеством Антони Сантоса, и произошло это в 1990-х годах.
Может быть, раньше кто-то тоже делал вставки из мамбо в бачату, но Сантос развил это.
А что такое ритм мамбо, можно посмотреть здесь:
http://www.youtube.com/watch?v=04JVl-AxXWs
В свое время мы разбирались в этом, вместе с Laalu, остальные видео с ритмами я выложу в дневнике, если кому-то это интересно.
Там же я выложила статью о развитии бачаты как музыкального жанра:
http://www.mambotribe.org/forum/blog.php?b=796.
В двух словах - бачата как музыкальный жанр возникла в 1960-е годы на основе болеро, но затем (80-90-е годы) испытала сильное влияние меренге, так что современная бачата (как музыка) - это результат смешения разных жанров, и меренге, конечно, в том числе.