(1) 12 belong to the same group, and on the 3rd, you can choose people in the same group. There are three options.

② 1, 2 different groups, 1, 2 choose the same group in turn, and the method is 4×3= 12.

Add up to 3+ 12= 15 species.

Another scheme: six people are arranged in a row, and the order is 12 in the same group, 34 in the same group and 56 in the same group.

Regardless of the order within a group, there is no order between groups.

So there are six! /(2! 2! 2! 3! ) =720/48= 15 species