I have looked into this before, not I gotta find it. Let’s start with an important issue. It isn’t the average temperature that will kill a naked person, and H. erectus was a naked of hair as we are. The thing that will kill an unclothed, without fire person is the extreme weather events. 8 hours of 18-19 deg F during a night, will probably do a person in. Why do I say that? Well, lock a person in a big freezer today, even fully clothed, they will probably die in that time frame. So let’s look at Dmanisi, Georgia’s temperatures this year. Febr 2020 had 19 days where the low was below freezing Most were in the 20s, but 2 days in a row were 18-19 deg F.
So now, let’s go back 1.77 myr ago when erectus lived in Dimanisi, which has an elevation of 4000 ft or so, about equivalent to eastern Colorado, Below is a glacial chart and you will see that it is at a time of more glaciation, but…
The average temperature of that glaication was about 3.7 deg C warmer than the Pleistocene glaciations. So, if Feb in an interglacial time today can get as cold as 19 deg F or -7.78 deg C (see chart below), let’s use this interglaicial winter temperture and add make it 3.7 deg C warmer.
| Fahrenheit | Celsius |
|---|---|
| 18 | -7.78 |
| 19 | -7.22 |
| 20 | -6.67 |
| 21 | -6.11 |
| 22 | -5.56 |
| 23 | -5 |
| 24 | -4.44 |
| 25 | -3.89 |
| 26 | -3.33 |
| 27 | -2.78 |
| 28 | -2.22 |
| 29 | -1.67 |
Doing that means the H. erectus will have to suffer through nights of 29 deg F, or -1.67 deg C. Do you think you can survive a night like that naked and without fire? My guess is no.
There is a strange study by the UK medical system where they tested people in houses with low temperatures, 17 deg c or so. The men war only light cotten pants and the women light cotton blouse and skirt. At 17 deg C they were taken right to the verge of hypothermia which is defined as core temperature at 35 deg C. I think this test was cruel, but they did it and got the data. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1604514/pdf/brmedj00448-0025.pdf
Now, I don’t think H erectus would have survived at -1.67 deg C naked at 4000 ft elevation, without fire and good clothing. And remember, it isn’t the average temperature that does the killing. It is the one bad cold front that is out of normal. If that happens once every 20 years, well, the population can’t make it much longer than that.