Mitochondrial Memes (Part 2: Aliens Within)

Part 1: Logos

Biologically 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, 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.)

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:

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

Is Race a Social Construct?

People mean a lot of things when they say “social construct.” Mostly they mean “made up.”

Luckily for us, Google is very helpful:

Dear Google and the NY Times: Not only is that not the biological definition of race, it’s not even the biological definition of SPECIES. This is not what laymen mean when they speak of race, not what racists mean when they speak of race, not what blacks or whites or Hindus mean, and definitely not anyone who actually studies human biology and genetics.

The simple folk definition of “race” is “a group of people who look kinda similar and come from the same large area of the world.” This, of course, absolutely exists. Most people in the world look a lot like their neighbors, especially if they live in their ancestral homeland and their country hasn’t been invaded lately.

Now, the exact details of how you racially classify people–are Hindus Caucasian? How about North Africans and Iranians? What about mixed-race people?–are socially constructed. This mean that a word like “black” may mean something different in Russian than it does in the Dominican Republic than it does in the US.

This does not change the underlying reality–the humans referred to as “black” still possess the quality of looking similar to other people from their ancestral part of the world. Reality does not disappear just because people sometimes disagree on exactly how to use words to define it.

The scientific, biological definition of race gets a little more complicated, since it matters whether we are talking abut chromosomal races, fungal races, or humans. A couple of definitions:

Geographical race

A distinct population that is isolated in a particular area from other populations of a species,^[9] and consistently distinguishable from the others,^[9] e.g. morphology (or even only genetically^[4]). Geographic races are allopatric.^[7]

Physiological race

A group of individuals that do not necessarily differ in morphology from other members of the species, but have identifiably different physiology or behaviour.^[10] A physiological race may be an ecotype, part of a species that is adapted to a different local habitat, defined even by a specific food source.^[11]

Notice that neither of these include, “possessing a gene or cluster of genes common to everyone in the race but to no one outside of it.”

But if you don’t like the Wikipedia, here’s what Biology Reference has to say:

The biological definition of race is a geographically isolated breeding population that shares certain characteristics in higher frequencies than other populations of that species, but has not become reproductively isolated from other populations of the same species. (A population is a group of organisms that inhabit the same region and interbreed.) Human racial groups compose a number of breeding units that in the past remained geographically and perhaps temporally isolated, yet could interbreed and produce viable offspring within the species Homo sapiens sapiens.

The Biology-Online Dictionary has some more definitions.

These races are real things, even if biologists disagree about exactly which race a mushroom should belong to.

The reality on the ground:

There are few truly isolated groups in the world, though the Onge (and most likely the Sentinelese) actually fit the NY Times’s wacky definition of a “race” due to thousands of years of isolation on tiny islands in the middle of nowhere:

From Haak et al.

The Onge are the peach stripe between the olive brown section and the purple section.

Major groups in this dataset, running from left to right (excluding the ancient skeletons at the far left):

Light Green: Brazilian rainforest dwellers who may be most closely related to Melanesians

Light Pink: Aztecs and their relatives

Brown: Canadian Indians

Green: Bushmen/San

Rose: North-East Africans

Dusty Blue: Bantus

Light Blue: Pygmies

Magenta: Tanzanian hunter-gatherers

Orange/Blue/Teal: Europeans

Orange/Purple/Teal: Middle Easterners

Olive Brown: Inuit (Eskimo)

Peach: Onge

Purple: PNG/Australia (Melanesians and Aborigines)

Light Green/Teal: India

Yellow/Red: East Asia

Yellow: Taiwan

Red: Siberia

Some of these groups have very mixed ancestries; people from eastern Canada or the middle of Eurasia, for example. Others are quite distinct–there is no doubt that the Eskimo and Pygmies are genetically distinct, physically distinct, geographically distinct, behave differently, and do not generally marry each other.

We may argue about whether Turks should be considered “Europeans” or “Middle Easterners,” or perhaps say that all orange people should be grouped together, or all teal or blue, but here geography does its job: Europeans look genetically like other Europeans; Indians look genetically like other Indians; Middle Easterners look like each other (except for Bedouins,) etc.

We may also argue about how many races we want to distinguish–people usually determine races based on whichever people are around, but obviously the world is more complicated than this. Americans generally think of “African Americans” as part of a broader race that includes all Africans, but we have distinguished here between 5 different groups, some of which are quite distinct–the ancestors of today’s Pygmies and Bantus, for example, split apart about 100,000 years ago, whereas the ancestors of today’s Bantu’s and Koreans split about 70,000 years ago (as far as we know.) Most African Americans are genetically Bantu (with a bit of European admixture,) not Pygmy. We might in a folk-sense refer to both of these groups as “Africans” or “black,” but genetically (and behaviorally) they are distinct.

Of course, you do not have to call them “races.” Most people studying human genetics use terms like “population,” “ethnic group,” “ethny,” or “clade” instead, but the practical meaning is the same.

But the idea that groups that are genetically, physically, behaviorally, or geographically distinct or distinguishable from each other do not exist is pure nonsense.