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I'm sorry if this is a stupid question, I'm just starting my first year of a biomedicine degree and I'm curious - googling didn't find me any answers.

I know that the Aboriginal Australians and many other native peoples have been wiped out by diseases such as smallpox, influenza, the common cold, and malaria. A lack of immunity to our diseases is currently an ethical concern of contacting previously uncontacted tribes.

Seeing as we can't properly develop full immunity to the common cold - as it's always changing - but we manage to always fight it off, and (I think) our immune systems are all fundamentally the same, why can't their immune systems just quickly learn to handle something like the common cold? Can't they simply develop antibodies? Why does it become fatal when introduced to a new group?

Thanks!

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I think your question stems from your assumption that different human populations share an immune system that is fundamentally the same. This is not the case. In fact, some of the greatest genetic variability in human populations can be found in the human leukocyte antigen (HLA) gene complex. The HLA genes codes for the major histocompatibility complex (MHC) proteins in humans. These cell-surface proteins are involved in regulating the immune system.

Different human populations have different levels of innate immunity to certain pathogens based on their historical exposure to different pathogens at different frequencies over evolutionary time.

I'm going to use the generic terms 'indigenous person/people' to refer to non-European indigenous people who encountered Europeans for the first time between the 15th-late 18th centuries. They can be Aboriginal Australians, Native Americans/First Nations, Amerindians, etc.

The primary reason that indigenous people were historically so vulnerable to European diseases is that the Europeans had been exposed to these pathogens for a long time, which led to them developing resistance to the pathogens. This is natural selection at work. The individuals most likely to survive were those with an immune system able to fight off those particular diseases.

Prior to European contact, indigenous people would never have encountered the pathogens that the Europeans brought with them, they lacked any immunity to them as a result. This allowed contagious disease like smallpox to spread quickly and kill a lot of people these groups.

You might ask why didn't Native Americans' diseases wipe out the Europeans when they came into contact with them?

One of the main reasons for that was domesticated animals. Europeans, by mainly the luck of the draw, had lived in close contact for centuries with a large variety of domestic animals, and thus, got exposed to a large number of species-hopping diseases, thus developing immunity. Native Americans had very few domestic animals, and got far less exposure.

References:
Riley E, Olerup O. HLA polymorphisms and evolution. Immunol Today. 1992 Sep;13(9):333-5. Review. PubMed PMID: 1361325.

Patterson KB, Runge T. Smallpox and the Native American. Am J Med Sci. 2002 Apr;323(4):216-22. Review. PubMed PMID: 12003378.

Markov PV, Pybus OG. Evolution and Diversity of the Human Leukocyte Antigen(HLA). Evolution, Medicine, and Public Health. 2015;2015(1):1. doi:10.1093/emph/eou033.

Guns, Germs, and Steel by Jared Diamond

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    $\begingroup$ To expand Its not that european population were not hit just as hard by these diseases, but they were hit that hard in the past, and one at a time. The europeans were getting hit one by one with these diseases as they evolved, while the native peoples are getting hit with several at once compounding the damage. $\endgroup$
    – John
    Apr 5, 2018 at 16:11
  • $\begingroup$ This is generally a good answer about an important aspect of the immune system that is variable and under selective pressure, but is not directly relevant to the question about the common cold. Most viruses associated with the common cold syndrome are poorly immunogenic, don't require antigen presentation for clearance, and so provide no selective pressure on HLA alleles. $\endgroup$
    – De Novo
    Jul 25, 2018 at 22:04
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Following on from @ValentinianMc's answer, Europeans may have been in contact with more people in total than native Americans and Australians. European populations would have had trade and contact with Asian and African populations. This could introduce more vectors for certain diseases (e.g. plague from Asia, via the Silk Road or Smallpox from Africa), which might have exposed Europeans to more pathogens than isolated communities. Exposure to diseases could possibly increase the Afro-Eurasian immunities to them. However, this also has the added effect of introducing epidemics such as the Black Death of the 1340s-50s, so it's not really a good thing to have more disease vectors.
However, this isn't to say that Native Americans were completely sparsely populated. In fact, the Aztec capital of Tenochtitlan was one of the most densely populated cities in the world (population ~250k in the 1510s). This might imply that the density of people is not the cause of the European immunity, but the total number of people in contact with one another.
You could also question whether differences (or the existence) of plumbing systems between Afro-Eurasian and other populations. If the Native Americans had a more advanced sewage system than European nations, they would be exposed to fewer water-borne diseases (and possibly not develop an immunity).
Lastly, the Colombian exchange was both ways and some evidence suggests that Europeans received (from Native Americans) an increased susceptibility to Rheumatoid Arthritis. This could demonstrate how all populations have diseases, and that the fact that Europeans fared better than Native Americans wasn't due to Europeans having any better overall immunity, it may have been the fact of which diseases were transmitted.

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