Links Post: Evolution and More

road-to-bigger-brains
From State of the Science: Finding Human Ancestors in New Places

The Puerto Rican rainforest is beautiful and temporarily low on bugs. (Bugs, I suspect, evolve quickly and so can bounce back from these sorts of collapses–but they are collapses.)

More evidence for an extra Neanderthal or Denisovan interbreeding event in East Asians and Melanesian genomes:

 In addition to the reported Neanderthal and Denisovan introgressions, our results support a third introgression in all Asian and Oceanian populations from an archaic population. This population is either related to the Neanderthal-Denisova clade or diverged early from the Denisova lineage.

(Congratulations to the authors, Mondal, Bertranpetit, and Lao.)

Really interesting study on gene-culture co-evolution in Northeast Asia:

Here we report an analysis comparing cultural and genetic data from 13 populations from in and around Northeast Asia spanning 10 different language families/isolates. We construct distance matrices for language (grammar, phonology, lexicon), music (song structure, performance style), and genomes (genome-wide SNPs) and test for correlations among them. … robust correlations emerge between genetic and grammatical distances. Our results suggest that grammatical structure might be one of the strongest cultural indicators of human population history, while also demonstrating differences among cultural and genetic relationships that highlight the complex nature of human cultural and genetic evolution.

I feel like there’s a joke about grammar Nazis in here.

Why do we sleep? No one knows.

While humans average seven hours, other primates range from just under nine hours (blue-eyed black lemurs) to 17 (owl monkeys). Chimps, our closest living evolutionary relatives, average about nine and a half hours. And although humans doze for less time, a greater proportion is rapid eye movement sleep (REM), the deepest phase, when vivid dreams unfold.

Sleep is pretty much universal in the animal kingdom, but different species vary greatly in their habits. Elephants sleep about two hours out of 24; sloths more than 15. Individual humans vary in their sleep needs, but interestingly, different cultures vary greatly in the timing of their sleep, eg, the Spanish siesta. Our modern notion that people “should” sleep in a solid, 7-9 hour chunk (going so far as to “train” children to do it,) is more a result of electricity and industrial work schedules than anything inherent or healthy about human sleep. So if you find yourself stressed out because you keep taking a nap in the afternoon instead of sleeping through the night, take heart: you may be completely normal. (Unless you’re tired because of some illness, of course.)

Interestingly:

Within any culture, people also prefer to rest and rise at different times: In most populations, individuals range from night owls to morning larks in a near bell curve distribution. Where someone falls along this continuum often depends on sex (women tend to rise earlier) and age (young adults tend to be night owls, while children and older adults typically go to bed before the wee hours).

Genes matter, too. Recent studies have identified about a dozen genetic variations that predict sleep habits, some of which are located in genes known to influence circadian rhythms.

While this variation can cause conflict today … it may be the vestige of a crucial adaptation. According to the sentinel hypothesis, staggered sleep evolved to ensure that there was always some portion of a group awake and able to detect threats.

So they gave sleep trackers to some Hadza, who must by now think Westerners are very strange, and found that at any particular period of the night, about 40% of people were awake; over 20 nights, there were “only 18 one-minute periods” when everyone was asleep. That doesn’t prove anything, but it does suggest that it’s perfectly normal for some people to be up in the middle of the night–and maybe even useful.

Important dates in the evolution of human brain genes found:

In May, a pair of papers published by separate teams in the journal Cell focused on the NOTCH family of genes, found in all animals and critical to an embryo’s development: They produce the proteins that tell stem cells what to turn into, such as neurons in the brain. The researchers looked at relatives of the NOTCH2 gene that are present today only in humans.

In a distant ancestor 8 million to 14 million years ago, they found, a copying error resulted in an “extra hunk of DNA,” says David Haussler of the University of California, Santa Cruz, a senior author of one of the new studies.

This non-functioning extra piece of NOTCH2 code is still present in chimps and gorillas, but not in orangutans, which went off on their own evolutionary path 14 million years ago.

About 3 million to 4 million years ago, a few million years after our own lineage split from other apes, a second mutation activated the once non-functional code. This human-specific gene, called NOTCH2NL, began producing proteins involved in turning neural stem cells into cortical neurons. NOTCH2NL pumped up the number of neurons in the neocortex, the seat of advanced cognitive function. Over time, this led to bigger, more powerful brains. …

The researchers also found NOTCH2NL in the ancient genomes of our closest evolutionary kin: the Denisovans and the Neanderthals, who had brain volumes similar to our own.

And finally, Differences in Genes’ Geographic Origins Influence Mitochondrial Function:

“Genomes that evolve in different geographic locations without intermixing can end up being different from each other,” said Kateryna Makova, Pentz Professor of Biology at Penn State and an author of the paper. “… This variation has a lot of advantages; for example, increased variation in immune genes can provide enhanced protection from diseases. However, variation in geographic origin within the genome could also potentially lead to communication issues between genes, for example between mitochondrial and nuclear genes that work together to regulate mitochondrial function.”

Researchers looked at recently (by evolutionary standards) mixed populations like Puerto Ricans and African Americans, comparing the parts of their DNA that interact with mitochondria to the parts that don’t. Since mitochondria hail from your mother, and these populations have different ethnic DNA contributions along maternal and paternal lines. If all of the DNA were equally compatible with their mitochondria, then we’d expect to see equal contributions to the specifically mitochondria-interacting genes. If some ethnic origins interact better with the mitochondria, then we expect to see more of this DNA in these specific places.

The latter is, in fact, what we find. Puerto Ricans hail more from the Taino Indians along their mtDNA, and have relatively more Taino DNA in the genes that affect their mitochondria–indicating that over the years, individuals with more balanced contributions were selected against in Puerto Rico. (“Selection” is such a sanitized way of saying they died/had fewer children.)

This indicates that a recently admixed population may have more health issues than its parents, but the issues will work themselves out over time.

Advertisements

Mitochondrial Memes (Part 3: Viruses want you to spread them)

Memetics is the study of how ideas (“memes”) propagate, using the evolution and transmission of viruses as its model. Ideas, like viruses, infect their hosts (human brains), then are transmitted to new hosts (other people.) A “successful” idea is one that spreads to lots of people, just as a successful virus is one that infects lots of people.

A new environment or technology can change the way memes propagate or the types of memes that are successful.

Note that this has nothing to do with the factual content of the idea, nor does it require humans to purposefully intend to make ideas more or less successful. More successful ideas will simply spread, whether anyone wants them to or not.

For example, as Moldbug writes on the evolution of modern Progressivism from mainline Protestantism:

The combination of electoral democracy and “separation of church and state” is an almost perfect recipe for crypto-Christianity. . . .

If you have a rule that says the state cannot be taken over by a church, a constant danger in any democracy for obvious reasons, the obvious mutation to circumvent this defense is for the church to find some plausible way of denying that it’s a church. Dropping theology is a no-brainer.

and Foseti elaborates:

The series begins by treating progressivism as a sort of infection of the mind. Assume progressivism is a virus that is solely concerned with spreading itself into as many minds as possible. We see the idea’s evolution, in which it starts as a fundamentalist religious belief and ends up discarding theism so as to better propagate itself in an officially secular system of government. Shed of overt theism, Progressivism “can be propagated by American official institutions, which are constitutionally prohibited from endorsing its ancestor or competitor [ie theistic Christianity].” The devil’s greatest trick . . . and so on.

In other words, the new environment (an explicitly non-theistic political arena) favors moral ideas that are not explicitly theistic.

Viruses are interesting things. They have a lot of the characteristics of living things–like DNA–but not all of them, and so are considered non-living or semi-living things. Critically, a virus cannot reproduce on its own–it must take over a living organism and hijack its reproductive mechanisms to begin producing copies of the virus.

800px-Phage_injecting_its_genome_into_bacteria.svg

Viruses (and other infections,) of course, do not “want” anything, because they are not sentient. But anthropomorphization is a convenient shorthand. Viruses which are spread far and wide “succeed;” viruses which infect one person and never infect anyone else “fail.” Therefore, chances are good that any virus you catch wants to be spread.

The common cold, for example, makes you sneeze, spreading the virus from your nose and mouth to all of your friends and family.

The parasite Toxoplasma gondii, which can only reproduce in the digestive tracts of felines but lives comfortably in just about any warm-blooded host, affects the brains of infected rats and mice to make them less fearful of cats, making them more likely to get eaten by cats, thereby transferring the parasite to its preferred home.

Horsehair worms infect crickets and then compel the crickets to drown themselves so the worms can reach water; liver flukes hitch a ride inside ants, directing them to the tops of blades of glass, where they are devoured by cows–the liver fluke’s destination. (source, with some interesting examples of pathogens that affect plant behavior.)

Immediately after infection, the flu virus makes people more sociable–and thus more likely to spread the virus to other people–before it floors you for the rest of the week. The awkwardly named IIV-6/CrIV virus is an STD that infects crickets, then makes them super-horny, spreading the STD to other crickets. Interestingly, the virus also shuts down the crickets’ immune systems, preventing them from having the “normal” cricket-responses to infection. Thus the crickets did not act or feel sick while going on their sex binge–until, you know, it turned their guts blue and killed them.

Alas, googling “Does AIDS make people horny” has returned zero hits I am actually willing to click on. But it stands to reason that STDs would increase their chances of successful transmission by making their hosts have more sex.

Memes also want you to spread them.

Any meme that can convince you to spread it–say, a meme that claims that it is immoral not to spread it–is a meme that is more likely to be successful than one that encourages you to keep your opinions to yourself.

“If you send this letter to 7 of your friends, you will have good luck! But if you break the chain, you’ll have nothing but bad luck for 7 years!”

“98% of people won’t repost this picture! Are you one of the 2% that’s brave enough to do it?”

One of the interesting things about the past 500 years or so of human history is that we have gotten better and better at spreading information. Not just chain letters and funny cat pictures, but also objectively valuable information like medical advice, scientific studies, cookbooks, and YouTube videos on how to get a small object out of your shower drain. (Get a vacuum cleaner, put a nylon stocking over the tube part, and suck it up.) Even thirty years ago, this blog would have been impossible–I would have had to content myself with slowly reading an encyclopedia, writing out my thoughts by hand, snail-mailing them to a few friends, and then waiting for a response.

If Voltaire were alive today, he’d write a blog instead of all those letters.

 

To be continued.

Mitochondrial Memes (Part 2: Aliens Within)

Part 1: Logos

150px-Biological_classification_L_Pengo_vflip.svgBiologically speaking, you are a member of the species Homo sapiens, (subspecies Homo sapiens sapiens.) Your genus is Homo–this includes all of our near cousins, like Homo neanderthalensis (with whom H. sapiens interbred,) Homo erectus, and the 2+million year old Homo habilis. Your family is hominidae, aka the great apes–chimps, gibbons, orangutans, gorillas, and us. We cannot interbreed with these groups. Your order is primates. The first primates probably evolved 65 million years (or more) ago; their modern members include apes, monkeys, lemurs, and lemur-like creatures like bushbabies.

Your class is mammalia–all animals with hair,[a] three middle ear bones, mammary glands, and a neocortex, at least according to Wikipedia. Most mammals have placentas and don’t lay eggs, but platypuses and echidnas have to be different. The first mammals appeared 225 million years ago.

From there, we head up to the sub-phylum Vertebrata, or all animals with backbones, then to the phylum Chordates, all animals with a nerve cord running down their back (but not necessarily any bones.) Chordates includes all birds, amphibians, reptiles, fish, and obscure creatures like salps, squishy, tubular creatures that look like jelly fish, and sea squirts, basically brainless tubes. Chordates appear to be over 500 million years old.

Next we have the kingdom Animalia, which includes all of the squishy things like sponges, jellyfish, octopuses, earthworms, and starfish, and crunchy things like insects, crabs, and spiders, in addition to us. The first fossil animals are 665 million years old, though older animals may simply not have been fossilized, due to being too soft. All animals are multi-cellular.

Above that, we have the domain Eukaryotes. All Eukaryotes have a nucleus and other organelles enclosed within membranes. Eukaryotes are divided into plants, animals, fungi, and protists, which are generally single-cells and include algae and the malaria parasite.

This is an animal cell, but all Eukaryotes are similar
This is an animal cell, but all Eukaryotes are similar, due to their nucleus (1) enclosed within a membrane (2) and other organelles.

There are two other major domains of life, bacteria and archaea, collectively known as prokaryotes. They have neither nuclei nor any other membrane-bound organelles. As distant cousins go, these guys are pretty distant–the common ancestors of eukaryotes, bacteria, and archaea lived over 1.6 billion years ago, possibly over 2.7 billion years ago (it’s really hard to find fossilized algae and bacteria.)

450px-Phylogenetic_tree.svg

Humming away inside your H. sapiens cells, making energy for you, are mitochondria. You might have heard that your mitochondria can be used to trace your maternal family line, because they 1. Are only passed down from mother to child (eggs have mitochondria but sperm don’t;) 2. Possess their own DNA, referred to as mtDNA or mDNA.

Why do mitochondria have their own DNA?

Because they aren’t human. They aren’t animals; they aren’t even eukaryotes. They’re prokaryotes, like bacteria.

Approximately one or two billion years ago, our ancestor–probably a primitive eukaryote cell–ate a prokaryote. But this prokaryote, by a great stroke of luck, didn’t get digested. Instead it got comfy, settled in, and stuck around. Here’s a helpful graphic to explain the process in more detail:

800px-Serial_endosymbiosis.svg

Yes, chloroplasts are prokaryotic invaders, too.

Mitochondias’ closest living relatives are the other Rickettsiales, an order of proteobacteria, which cause a variety of diseases including Typhus and Q fever. Luckily for us, our mitochondria help keep us alive, rather than kill us.

Part 3: to be named