I am not sure what other side of an Argument he might learn.
Is there an Argument and if so, what is it about? Evolution?
If it is Evolution, it is as much an accepted science as many of your other elementary school science teachings to include the Water Cycle Theory, The Tectonic Plate Theory, the Heliocentric Theory . . .
If it is abiogenesis, than there are just a few hypothesis but nothing that has reached Scientific Theory as of yet.
While I don't agree with that type of parenting, if your brother is under the age of 18 then he is beholding to your mother's wishes. Tell your brother that he can think of it as a sociological or psychological study of ancients traditions turning from believed truth to myth. He can compare and contrast with other such religions that are now regarded as myth.