simple, the girls liked girls, the guys liked guys...
the baby (neutral for now) was genetically predisposed to like either guys or girls as both were a possibility... and received / did not receive the chromosome to make it the opposite sex as to what it was attracted to
a better experiment would have been a straight person and a gay person of opposite sex producing offspring, as both parents are attracted to the same sex... genetics would perhaps cause the child to be attracted to that sex no mater what the sex of the child... however it is often the case that a gene skips one or more generations...
in all actual fact I highly doubt that this is an inherited gene at all...
all evidence I have though, is that since I first was physically attracted to people it has always been those of the opposite sex... so I believe that it is something you are born into, however there is no reason to believe that a persons up bringing can or cannot change that... the whole nature vs nurture argument... which I think is just a big load of s*** as it is actually both, you are born into some traits while others are developed and or more defined through your upbringing.
inb4 fake science.
owait