Kathryn Posin Dance Company returns to the 92nd St. Y’s Dig Dance Series with three Posin premiers: “Evolution: The Letters of Charles Darwin,” a whimsical multi-media romp through the life and letters of Charles Darwin with text drawn from his correspondence; the edgy “Triple Sextet,” to Steve Reich’s Pulitzer-Prize-winning “Double Sextet”; and “Memoir,” a solo created for noted artist and company co-founder Lance Westergard.