# In addition, evolution cannot explain the many complex sex-determining systems. For example, in most mammals, females have two identical sex chromosomes (XX in this case) whereas males two different ones (XY.) However in birds, reptiles, many insects, and other organisms, the situation is reversed to where the male has two identical sex chromosomes and the female has two different ones; for example male birds have a ZZ chromosome pair and females ZW. No evolutionist has proposed a mechanism by which mammals could have a different sex chromosome system from the reptile ancestors they allegedly share with birds. | # In addition, evolution cannot explain the many complex sex-determining systems. For example, in most mammals, females have two identical sex chromosomes (XX in this case) whereas males two different ones (XY.) However in birds, reptiles, many insects, and other organisms, the situation is reversed to where the male has two identical sex chromosomes and the female has two different ones; for example male birds have a ZZ chromosome pair and females ZW. No evolutionist has proposed a mechanism by which mammals could have a different sex chromosome system from the reptile ancestors they allegedly share with birds. |