Daniel Lemire's blog

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Science and Technology links (April 13th 2019)

12 thoughts on “Science and Technology links (April 13th 2019)”

  1. Andrew Dalke says:

    I have several issues with the trichromacy paper. The most critical is that there was no attempt to determine if people with ‘lifelong dichromatic experience’ had a different response rate. That is, if the results are the same with trichromatic and dichromatic people then the test is useless for the purpose described.

    I remember watching a video about the difficulty in finding people who are functionally tetrachromatic. The researcher made two materials with colors which were not supposed to be distinguishable by trichromats but could be distinguished by tetrachromats. However, some people could tell them apart, including some men. For genetic reasons, tetrachromatic vision requires two X chromosomes. Thus, that test was flawed.

    Similarly, this paper constructs images by applying results from a couple of previous papers, but doesn’t demonstrate that those images are indeed not distinguishable by dichromats.

  2. This all sounds highly speculative to me… but the reason I shared this link despite its speculative nature is that we are often told that we learned to distinguish colors so well as a way to avoid predators.

    1. Andrew Dalke says:

      I can’t comment on how you heard about the origin of trichromacy, but the academic research doesn’t seem to regard predator recognition as the most likely reason.

      For example, this paper says “A popular account suggests that trichromacy was selected to aid primates in foraging by facilitating the detection of ripe fruit against green leaves … there is support demonstrated for this hypothesis … Other theoretical accounts of color vision variation in primates that have received less empirical attention include camouflage detection, predation detection, and nocturnal versus diurnal activity (see Kawamura & Melin, 2017, for a comprehensive review).”

      That’s a book chapter. As an alternative source which I could read, I found “Trichromatic Color Vision in Primates” by Michael H. Rowe at http://neurosciences.us/courses/vision2/Color/rowe.pdf from 2002. The hypotheses listed are “the suggestion that L cone pigments and primate trichromacy evolved as an adaptation for detecting fruit against a background of green foliage” and “An alternative hypothesis, that leaf consumption rather than fruit consumption is the principal factor in maintaining trichromacy, has also received support in a recent paper by Dominy and Lucas”. Predation wasn’t mentioned.

      1. I am not surprised that you found references that do not allude to predation, I am not claiming that it is dominant view… but it is certainly something that is being offered

        By combining color vision modeling data on New World and Old World primates, as well as behavioral information from human subjects, we demonstrate that primates exhibiting better color discrimination (trichromats) excel those displaying poorer color visions (dichromats) at detecting carnivoran predators against the green foliage background.

        Again and again

        Many primate species maintain a polymorphism in color vision, whereby most individuals are dichromats but some females are trichromats, implying that selection sometimes favors dichromatic vision. Detecting camouflaged prey is thought to be a task where dichromatic individuals could have an advantage.

        Let us be clear: I am not making any specific claim regarding this question. I just thought that the latest research was interesting.

        1. Andrew Dalke says:

          I also want to make it clear that I wasn’t saying predator recognition isn’t a proposed reason. I even included that hypothesis in the quotes I copied from the Thorstenson et al. paper you originally pointed to.

          I wanted to contrast your statement “we are often told that we learned to distinguish colors so well as a way to avoid predators” with (quoting now the first of your two latest references) “current explanations focusing almost exclusively at the advantages in finding food and detecting socio-sexual signals”. Where and when did you hear about the predator hypothesis?

          That first reference gives a lovely explanation of why there’s no a priori reason to think that trichromats are better at detecting predators then dichromats: “Two hypotheses could be drawn:
          first, that trichromatism should be advantageous in identifying
          conspicuous predators against a green foliage background, as it happens for primates of conspicuous colorations (e.g., golden lion tamarins) [Sumner & Mollon, 2003]; second, that dichromatic primates should use achromatic information (e.g., shapes, outlines, and textures) more effectively to break
          predator camouflage and outperform trichromats, in the same way they might do when foraging for insects”. Hence the need for experimental research.

          BTW, your second reference concerns camouflaged prey (“how quickly humans could detect cryptic birds (incubating nightjars) and eggs (of nightjars, plovers and coursers)”) and not of humans avoiding predators.

          I agree that it’s an interesting topic, which is part of why I looked into it in more detail.

          1. Where and when did you hear about the predator hypothesis?

            I have been told, I don’t remember when, that human beings are among the few mammals who can spot a tiger in bushes.

  3. Vadim Ivshin says:

    Last link is broken, I guess.

  4. Jouni says:

    The Danish lifecycle assessment of grocery carrier bags doesn’t claim what it is said to claim. The 7000x/20000x difference between cotton bags and plastic bags is the maximum over all criteria, not the overall difference in environmental impact. The biggest difference is in the ozone depletion potential, but even there the absolute numbers are low. It would be significant if every person in the world bought a new cotton bag every day, but the numbers are negligible in any reasonable scenario.

    All the numbers are low for all carrier bag types anyway. The real message should be that it doesn’t matter what kind of bag you use, if you keep reusing it as long as it’s reasonable, and properly dispose of it when reuse is no longer reasonable. More generally, single-use plastics aren’t that bad, as long as the waste will be disposed of properly. Unfortunately plastic is often used in situations, where people don’t care what happens to the waste, and it’s not realistic to expect them to care.

  5. Tomasz Jamroszczak says:

    “Cotton bags must be reused thousands of times before they match the environmental performance of plastic bags”

    There are a lot of assumptions in the paper, incineration, disposal within Europe, most notable being:

    This assessment does not take marine litter into account

    1. Indeed, the plastic bag article seems only to be measuring the manufacturing side of the cycle, and paying no attention at all to disposal.

      As a farmer, I can say that over time, dozens of plastic bags blow onto my property every year – and that is only 34 acres. Cotton based bags (and I don’t see any) would be no problem because they would harmlessly decompose. The plastic bags persist (in ripped up form) years, and they can be ingested by livestock – and cause severe problems for some animals.

      This is the reason to use cotton bags – disposal. Not manufacturing costs (environmental or otherwise). People are careless. Winds are strong.

      1. I find this compelling.

      2. Andrew Dalke says:

        Not just marine litter. The study says: “The effects of littering were considered negligible for Denmark and not considered.”