Researchers in Carlos Bustamante's lab at Stanford have recently compared the Y chromosomes of humans and Neandertals. They exome'd an exhumed 49k-year-old Neandertal male from El Sidron, Spain and found that his Y chromosome was not one that has been observed in modern humans. That is, his Y is likely extinct, gone from among the living.
About a month ago, I wrote about how the offspring of human and Neandertal matings couldn't have all been "mules" (couldn't have all been sterile), as some of us have Neandertal DNA in us. But what Bustamante's research reveals is that there were some male Neandertals who may not have mated successfully with humans (the success here being a fertile child), and they provide intriguing speculations about why.
Some of the genes on the Y chromosome can cause immune ruckus for the pregnant, whose male fetuses begin to express their male-specific histocompatibility genes. This can lead to miscarriages. Furthermore, (and equally fascinating) is that there are Neandertal and human-unique mutations on the Y chromosome in genes that are, in fact, histocompatibility genes. It's possible that these lineage-bound differences were incompatible with life when present in the fetuses of male human-Neandertals, perhaps explaining the absence of Neandertal Y in modern humans. As the authors muse, this is consistent with Haldane's rule: if one sex is absent, rare, or sterile among the the first generation matings of different groups, that sex is the heterogametic sex (the sex with the differing sex chromosomes; e.g. X/Y for males).
Mendez, F. L., Poznik, G. D., Castellano, S., & Bustamante, C. D. (2016). The Divergence of Neandertal and Modern Human Y Chromosomes. The American Journal of Human Genetics, 98(4), 728–734. doi:10.1016/j.ajhg.2016.02.023
Shift work–working outside of 9 am to 5 pm–is a feature of our modern, 24-hour economy. 20 percent of us in the developed world do it full-time. But shift work involving circadian disruption is also a probable carcinogen, classified as such in 2007 by the International Agency for Research on Cancer. The evidence in animal models for the carcinogenicity of circadian-disrupting exposures is strong, and, as the evidence in humans emerges, we see a consistent picture across three cancer sites: long-term shift workers are at a modestly increased risk of breast, prostate, and colorectal cancer. But this knowledge is difficult to grasp. It’s like the live lobster slowly cooking to a boil. And why am I telling you this? Well, first, a lot of us work weird and long hours. But shift work is just the most extreme circadian disruptor. Most of us stay up late in front of our computers, engrossed in social media, movies, and work. And some of us even take our devices with us to bed (I’m guilty). Light-at-night is a circadian disruptor. It stops the release of melatonin, which is our body’s chemical message of darkness. Unlike shift workers, though, most of us do eventually get some shuteye and a nice dose of melatonin each night. But we could do better, as not getting quality dark time activates the stress response and suppresses the immune system–this is in addition to the problems of not having a steady flow of melatonin–which compromises our ability to handle all the demands that keep us afloat.
But have you ever tried to break yourself of the itch to check email one last time? Not only are we addicted, but light-at-night is part of our social being. This means that we are extremely unlikely to give up the hold that this technology has on us without changing our culture. The developed world needs leaders who turn out their lights and go to bed without their iPhones. But I’m not putting my phone away unless you do. That’s right. Somehow we need to know that this is an activity we are doing together.
I need to know that you know that I know that you know that we are turning off our lights.
I'm a Public Health Genetics PhD student at the University of Washington and a molecular epidemiology research fellow at the Fred Hutchinson Cancer Research Center. I post (mostly) about topics in epidemiology and genetics.