Past studies have shown that humans can recognize the voice of a friend after hearing just two words with 90% accuracy, and that babies recognize their mother’s voice at birth. I’ve never found an answer to the question of how many voices we have stored this way, and I wonder if it might be up to Dunbar’s Number—the number of social contacts we’re able to store and keep track of without external support systems. That number, around 150, is thought to govern the tribe sizes in hunter-gatherers, among other things, and thus has a large influence human cognition and history.
I always think of this when I notice a celebrity voiceover. If I recognize John Krasinski in an Esurance commercial, does that mean he’s in my tribe psychologically, even though I don’t actually know him? What a strange world we live in.
Anyway, this week’s SciKu was inspired by research out of U.C.-Berkeley showing that zebra finches are also able to recognize the voices of their friends in this way, right up to their own “tribe” size of 50. The thought of finches twittering to their friends made my day.
all these years
your voice on the phone
Photo: Figure 1 from “Biofluorescence in the platypus,” Mammalia, 15 Oct 2020
This Sunday’s #sciku is about the recent accidental discovery that platypuses have fluorescent fur, joining a surprisingly wide phylogenetic range of mammals to feature the trait. Opossums, flying squirrels, and platypuses diverged from each other over 20 million years ago, and yet they all glow in UV light. What’s interesting is that we had no idea they were fluorescent, and still don’t know why it’s adaptive. It seems to be a feature of nocturnal mammals, so likely involves either intra-species signaling—perhaps a sexual fitness display?—or a kind of camouflage to hide from UV-sensitive predators. None of the articles make much of it, but notice in the photo how the coloring is completely different on the dorsal (back) side compared to the ventral (stomach) side. That reminds me of the coloring patterns on sharks and military aircraft, that camouflage themselves differently for those looking from below than those above. Flying squirrels are the same, only glowing on their bellies. Makes me think it’s more about hunting than being hunted. Platypuses eat things like shellfish and aquatic worms, which also bioluminesce. My hunch is that they’re fooling their food.
Anyway, we only discovered glowing squirrels a few years ago, and platypuses this week! So much of nature leaves us in the dark.
the neighbors throw a party
Apparently, the average human body temperature has been decreasing since the beginning of the Industrial Revolution, when Carl Wunderlich’s records established 37 C (98.6 F) as the norm. In the U.S., it’s declined by 0.03 C per decade, and is now as low as 36.4 C (97.5 F).
The theory has been that increasing access to modern vaccines, antibiotics, and clean drinking water has decreased the body’s background inflammatory response—but it wasn’t proven. This study out of U.C.-Santa Barbara does that, using health data from a group of farmer-gatherers in the Bolivian Amazon, who have been undergoing rapid changes in their access to healthcare over the last two decades because of new social programs in Bolivia. The team found that, indeed, the average body temperature of the Tsimane began at 37.0 C and has decreased by a full degree after these government interventions.
This is all new to me, and made me think about how everything is economics. There’s an energy cost to maintaining a higher basal temperature, and being able to use that energy elsewhere is a bio-economic transaction. And where is that extra capital we’re given by modern medicine spent? Could this be why other studies show that general intelligence has been increasing over the last two centuries, as well? Or do we just store it for the future as fat, which is also increasing?
And then the fact that we’re becoming more cold-blooded as a consequence of that bio-economics reminded me of the studies suggesting that wealth decreases empathy—a psycho-economic transaction, where decreased vulnerability leads to a decrease in reciprocal altruistic reward. The famous study shows that more expensive cars are less likely to stop for pedestrians at a crosswalk.
So everything is economics, on every level, including the prosperous but cold math of the global economy expanding its reach into the Amazon. As always, it was fun trying to cram all of these thoughts into a tiny Sunday sciku.
we find it healthy to grow
For a long time I’ve been interested the Snake Detection Hypothesis, which says that it was primates’ co-evolution with snakes that allowed for the rapid development of our excellent vision—we had to be able to quickly recognize camouflaged snakes so they wouldn’t kill us as we coexisted for millions of years in the same habitat. My hunch has been, though I’ve never found any research on this topic, that it’s this same high-contrast pattern detection that allows us to read text, and that the “visual word form area” of the brain is an adaptive overlay on top of the snake detection area. If you look at the pattern on a snake, it kind of looks like text. Which has cool implications for the Eden myth, where it was the snake that taught us knowledge. I have no idea whether or not this is true, but it would be interesting if it is.
Anyway, this paper points toward that hypothesis, showing that the visual word form area is pre-wired into the brains of infants. They put 40 newborns into an fMRI machine and showed that they already have the VWFA. Which begs the question—how could this module have already evolved when majority literacy (let alone universal literacy) is only 75 years old? In 1820, only 12% of the global population could read—yet we already have a pre-wired VWFA just 200 years later? How is that possible? My answer: snakes.
your first words
snaking across the page
parting the grass
A lot of the cool things about this story are in the science paper but not the article: They found mile-long tracks at White Sands National Park and determined it was a girl carrying a toddler, shifting the kid from one hip to the other and occasionally putting it down. She walked in a straight line like she knew exactly where she was going, at about 3.8 mph, so a brisk pace, and then followed the same path back a few hours later without the toddler. During the time in between, a giant ground sloth and a mammoth crossed her tracks. The mammoth just kept walking, but the ground sloth sniffed, then stood on its hind legs to look around, seemingly worried about human predation. A whole mysterious story in these tracks—and what happened to the toddler?
such a long walk into the future fossil