- High levels of solar radiation negatively impact the survival of humans because it affects human food sources like crops and love stock. They might not be able to survive the higher levels of radiation. It makes it harder for people to keep there core body temp down to 98.6 F because the increase in heat.
Short term
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Facultative
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Developmental
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Cultural
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| squinting to protect eyes from sun. | increased melatonin production in skin. making skin darker to protect from sun. |
Natural selection favoring more slender bodies that retain less heat. Bipedal walking less surface area for radiation.
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Technology, clothing, housing, sunblock, umbrellas
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- The benefits is that we get to learn why people developed the traits they have and what we can do to adapt to our changing environment better.
- People who live in areas where solar radiation is stronger like tropical area would have darker skin to protect themselves from the radiation. The study of environmental influences on adaptations is a better way of understanding human variation because “race” does not categorize people into groups with similar variation to study the way a groups environment influence their traits would be a better method because that’s how one would learn how they have adapted to that environment. For example you can learn that as a result of radiation in Africa the people are darker to adapt. Or maybe it was “sexual selection” as some scientists think it is. Another example would be head shape; you can really infer that this “race” has this head shape because it varies.
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| Facultative |
| Developmental |
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| Cultural |
I think what you are doing in your first section is equating solar radiation with heat stress. Yes, solar radiation might affect crop plants but they have adapted to radiation levels just like humans. Aside from that, we are discussing human adaptations here, not plant adaptations.
ReplyDeleteExposure to the sun in equatorial zones will make it more difficult to maintain core body temperatures but this is due to heat stress, not solar radiation stress. Solar radiation stress is two-fold: One part is the possible damage to the skin caused by radiation, and the other is a positive effect of vitamin D absorption from the sun. Populations at the equator have darker skin to protect against radiation and still are able to absorb sufficient vitamin D. As you go farther from the equator, the intensity of vitamin D from the sun lessens, but so does the radiation stress. That means populations farther from the equator can adapt with less melanin (because they can) so that they can absorb sufficient vitamin D. Evidence of this is that people who trace their genetic history to equatorial regions and have high melanin levels have difficulty absorbing enough vitamin D if they live closer to the polar regions.
I agree that squinting could be seen as a means of protecting the eyes from sun damage. Otherwise, there is no short term adaptation to solar radiation damage to the skin. That is why it is such a dangerous stress.
Good job on your facultative trait.
Longer, leaner bodies help with heat stress, not solar radiation stress. But I agree that bipedal locomotion has been suggested as a possible adaptation to solar radiation (and heat) stress. A more common example are the different base levels of melanin in the skin, with populations being darker from birth nearer the equator and other populations being lighter skinned at birth farther from the equator.
Sun screen is a cultural adaptation to solar radiation, as are clothing and umbrellas.
Okay on section #3. Expanding upon your explanation would have been a good idea to clarify. The importance here is in the word "why". The adaptive approach goes beyond just describing traits to actually explaining the reasons why humans look as they do.
Okay in your final section... I think you meant "can't really infer" in your final sentence? Race is a subjective system of categorization, nothing more, and differs from culture to culture. As such, it can't be used as a basis to objectively understand biological traits.
Hi Judy,
ReplyDeleteI found your blog to be very interesting, and I thought it was a good idea to choose solar radiation. I had a lot of trouble fully understanding this topic, but it is clear that you understood it. I completely agree with you that the benefit of studying human variation is that we can see which traits were developed to help adapt to the environment. I also agree with you on the subject of studying “race” not being the best way, because we do not categorize people by race, but more by environmental adaptations. I enjoyed reading your blog, and your point of view on the subject, great post.