It was so bad that I was even looking forward to seeing Ed, my boss, when we docked with today, as I could then go home and forget these dreadful people. So as soon as I felt the timeship settling into its home cradle I wiped condensation off the porthole expecting to see him looking in.
Ed's not perfect. Like all bosses he has some personality defects, he's no good on technical stuff, he can't be objective in appraising his staff, he lacks a few basics like charisma and all other good points, but at least he is a mammal and his head points forward. The thing I saw through the porthole had a head mounted sideways and the face of a Picasso model.
'Ed' was equally horrified to see me, but must have immediately drawn the same conclusion I did - we'd drastically changed the past and survived now only as long as the timeship was still sealed. It enthusiastically attacked the seal, knowing we'd disappear if the ship opened. This is what I hate about creatures working in time travel in the alternative timelines, they always want to preserve their own faulty realities. It would be much better if they were trained to help people like me when we need to restore the one true timeline.
So, I pushed the Chronometric Lever hard over to Devonian and turned to face my companions during the long journey back.
"Someone changed the past. Those flatfish we saw were meant to turn back upright before giving rise to all the vertebrates, but now they didn't. I'd bet every vertebrate in the modern world has its head on sideways, and it's someone's fault."
O'Kelly looked sheepish, and reaching into a pocket muttered something about souvenirs as he pulled out a very unhappy-looking flatfish.
"Quickly!", I shouted, "It may not be quite dead, give it the kiss of life!"
McLeod looked skeptical as O'Kelly locked his lips to the horrible thing and blew for all he was worth, she said quietly "Surely it doesn't actually breathe air, apart from predating lungs by a long time?"
"Well, yes", I admitted as quietly, "But watching him do that makes me feel better while I think about this."
"But how can this happen, surely if history can be changed no-one would be allowed time tourism?"
"It doesn't happen very often, there are only a few stable timelines and it takes a very lucky change to jump to the next groove. We must have taken out just exactly the wrong fish, so now we need to recruit a new universal ancestor for the backboned creatures."
She didn't like this explanation, "But tourism can't justify even a small chance of something this bad happening?"
"That's like saying the Roman Empire wouldn't let itself be overrun by barbarians rather than divert manpower from wine-making to the army. Or that the late industrial age wouldn't burn the last of the fossil fuel to cause global eco-catastrophe rather than adopt sensible technology. Or that Pleistocene hunters wouldn't wipe out new food megafauna as soon as they meet them. All societies are willing to destroy themselves rather than accept a minor inconvenience - it's human nature."
"I don't mind being a stabaliser for a flatfish, but we seem to be changing their behaviour rather than their genes. Isn't this Lamarckian evolution, based on inheritance of acquired characteristics, the theory that turned out not to be true? Surely we should be killing all the ones swimming sideways, using proper Darwinian principles?"
"They're all swimming sideways, killing all of them won't make them evolve: we have to train them.", I said, wrenching a particularly stubborn one upright and trying not to let her see its fin come off in my hand. I went on quickly "Genes for swimming upright can only be positively selected if they're helpful, which only happens in fish who already do it, so they have to learn before they can evolve that way."
She thought about this while prizing one of the shyer flatfish from a rock crevice, allowing me time to hide the loose fin and discard the broken fish with an expression implying it was a useless mutant anyway. Then she said,
"So we have to act as if Lamarck was right, although he wasn't, because it works."
"Yes, it's like using Newtonian mechanics for everyday purposes although we know it's not true in the Einsteinian sense. Most scientific theories are complicated replacements for easier ones that explained the same results in a less clever way."
"I see, it's a first order heuristic, like 'All men are bastards'?"
"Ah, vaguely like that, yes."
So this time we approached the present day with confidence, and as I wiped away the porthole's condensation I saw Ed's delightfully forward-pointing face looking in at us. He seemed a little concerned at how much I'd worn out, and aged, my tour group, but for once I was even looking forward to being told off.
As I broke the seals and we climbed out, McLeod had the expression I recognised as thought leading to problems, so I asked Ed to pause in the tirade I wasn't listening to and waited for her to speak.
"It's probably nothing, but I seem to remember that the right side of my brain controls the left side of my body, and vice versa. Was that always true?"
"Er," I said, "I remember that too, but we can't tell now what was true before we broke the seal, we're part of this timeline."
O'Kelly contributed unhelpfully, "I don't remember that. Does that help?"
McLeod went on, "So, we turned those fish the wrong way, adding another ninety degree twist instead of reversing the original twist. All vertebrates who ever lived have had their heads on backwards"
There was silence until I looked at Ed and pointed out "There's no way to prove this is a change, and even if it is, it's not my fault."
But I could already see the future, another bad appraisal.