when I worked at the dairy, there was this girl, Pam. Pam worked just as hard as the guys and did a lot of the same things (at least, the things they let her do). The "guy tasks" she didn't do were not because she couldn't, but because our boss would not let her learn. When I left the dairy, she was JUST being allowed to do "scary" things like *gasp* feeding the cows. and she'd worked there for two years!! There's no heavy labor in feeding. You move the feed into the feed cart with a skid-steer (bobcat). You push some buttons on the feed cart. you drive the feed cart down the aisles. YOU PUT THE AISLE CHAINS BACK UP SO US PEOPLE MOVING COWS DON'T HAVE LOOSE COWS EVERYWHERE (*twitch twitch the guys were horrible about this. One idiot did so on the last set of chains that I can't see from the parlor and I lost a dozen cows to the field...and when I hollered at him over the sound of the feed cart to come and help, he swore that he'd see to it that I never worked there again...despite they fact they've been explicitly told to put the chains up and that it is not the milking assistant's responsibility to do so. and the bad part? Our boss showed such favoritism to the guys (particularly the feeding guys) that it was possible that I might be fired over someone else's stupid mistake, particularly if he didn't give me a chance to tell my side first. Luckily, our boss was out of town that weekend and our manager is much more sensible than he is.

sure, you could make the argument of "well the guys worked harder and did tougher tasks". The problem with that argument, the only reason the guys did the welding and tractor work was because our boss was sexist pig who wouldn't let girls who grew up on farms welding and hauling tractors do so.

so yah, the guys got paid more...but did it have any logical explanation besides the boss's sexism? No...no not really.