I’ve read that human beings haven’t changed much physically for the past 40,000 years or so. What if you could transport a human from that era into our present one? Maybe we have changed quite a bit physically, but we just don’t really have a way of measuring the changes. What do you think the most significant physical differences would be between a modern human and the historical one? Exposure to what would kill the human first? I’d imagine it would be something like a bacterial or viral infection. Do you think the human would hear things that we automatically tune out? There must be a huge difference between the amount of electromagnetic waves bouncing around now as compared to then. Could that mess the human up also? Never mind the air-born viruses and bacteria, what about air pollution and other changes in the atmosphere? That human could probably breathe, but for how long?
Educated guess follows, pending the arrival of experts.
I would suspect that the biggest threat to your hypothetical time travelling Cromagnon pal would be bacteria and viruses. Since these critters adapt to our immune systems fairly rapidly,there’s a good possibility that Og (or whatever his name is) would come down with a bug his immune system just isn’t prepared for.
As far as pollution, noise, and electromagnetism, there hasn’t been a particularly elevated amount of these around long enough to provide much Darwinian pressure. I doubt we’re significantly more resistant to electromagnetic waves than Og is. Most modern hazards just aren’t immediately debilitating. Long term health effects don’t matter to Mother Nature unless they result in fewer successful offspring. Of course, one could also argue that darwinian pressure tends to favor the poor (generally, they have more offspring than the rich). 
~~Baloo
I don’t know about 40,000 years ago, but the average man is 6 inches (15cm) taller than he was only 100 years ago. I’d say that is a significant physical change.
To be fair, you should bring Og here just as he or she is born. A lot of adapting to our environment occurs as a very young child (like developing defenses to bacteria and viruses). You might have an equally hard time if you were transported 40,000 years into the past, with viruses which have since vanished.
I’ve got to go with the ‘germs are going to kill him’ assumption, but for slightly different reasons. I don’t know if there’s any reason to believe there are any germs floating around in the world now that people weren’t coping with 40,000 years ago, I can’t think of any. Sure some mutate, like the post WWI Spanish 'flu virus, but the chances are they wouldn’t be particularly more devestating to a person from 38000 bc than to the people they affect today. The few exceptions might be the really common ones that we get a chance to develop resistance to due to colostrum (mothers milk).
What has changed is the geographic distribution of most of these diseases. A person from that period would only have been exposed to a few local diseases, whereas most infectious diseases now have worldwide distibutions. This means that a person from any given area from 40,000 years ago will have about the same chance of succumbing to a disease as an isololated Amazonian Indian from today, or a New Guinean Highlander from 60 years ago, or a North American Indian from 300 years ago. Nothing to do with his age or the way bugs adapt, just his geographic isolation.
I can’t think of any reason why a person of that time would be more likely to tune out or hear anything different from any other culturally isolated person, whether Amazonian Indian or Kalahari Bushman. These were modern Homo sapiens sapiens just like you and me. If there were any physical differences from this time period they haven’t shown up on skeletons or artwork, nor are any cultural changes apparent from the remains of religious ceremonies.
The one change we do know of is that people have shrunk somewhat over 30,000 years, by about 9%. What USCDiver has pointed out is apparently the result of a recent dip caused presumably by the agricultural revolution and resulting overcrowding/dietary deficiencies. Judging by teeth sizes (and there are more teeth than any other type of early human remains) early humans were somewhat larger than modern humans.
Oh, and one last point, Neanderthals were still around until 35,000 y.a., so if you just select a random person from 40000 y.a. you could get a 5’3" 200 kg man with a sloping forehead, or possibly a human/Neanderthal hybrid.
Thankyou all for giving me some answers. I never even thought of the fact that there are peoples in cultural isolation today (or at least pretty recently), and none of them have ever asked “Can’t you HEAR THAT? It’s driving me NUTS!”. That was one of my favorite little ideas, that all of the electromagnetic waves bouncing around now would have some sort of effect on a person who hadn’t been exposed to them.
I really do appreciate the thoughtful insights, such as viruses back then that would kick the snot out of a modern era time traveller, the effects of geographic isolation, and the fact that most of the differences in the environment would have more long term effects as opposed to short term.
It seems very easy to forget just how much geography has been a factor in our development as those physical boundaries seem to shrink more and more quickly with the passing years. Add in the dilution of cultural differences coming about by these disappearing boundaries, and it seems to me we are becoming a less diverse and interesting species as a whole. How long will it be before the difference between various cultures is almost negligible? So many things are stored in electronic media, what happens if the printed word becomes nearly non-existent? What will take the place of religion as one of the defining characteristics of a society? Is marriage also becoming a vestigial institution? Where does a person fit in any more?