What Are Cataracts?

This question came up because my son’s babysitter is fostering a blind dog – an adorable little black poodle with milky white eyes named Rosie.

Seriously. How cute is that?

My son and his babysitter’s two children love her and spoil her and carry her around, and they describe her as having “moon eyes” because they sort of look like full moons. The Peppermint Pig Animal Rescue was going to get her eyes operated on to remove the cataracts, but it turns out she also has detached retinas. So the surgery wouldn’t really change anything for her.

We were talking about the dog, and the news, and my son asked “what are cataracts?” Because we’d used the word and he didn’t know it.

“It’s what makes Rosie’s eyes white,” my wife replied.

“But what are they?” he replied.

“It’s…” My wife thought for a second. ‘It’s like a film on her eyes, that she can’t see through.”

“But why are they called that?” my son persisted.

So. What are cataracts?

This. This is a cataract.

I’ll be honest, here. I don’t actually know. My wife’s explanation seemed as good as any, and I think I always sort of assumed that they were something like scar tissue. But, like with so many other things, I’ve never really stopped to ask what they were or what causes them. So, since my son asked, it’s time to change that.

Definition

Merriam-Webster, my go to for dictionaries thanks to a handy app, gives two definitions for “cataract“:

  1. [Middle English, from Medieval French or Medieval Latin; Medieval French catharacte, from Medieval Latin cataracta, from Latin, portcullis] : a clouding of the lens of the eye or of its surrounding transparent membrane that obstructs the passage of light
  2. a obsolete : waterspout
    b : waterfall; especially : a large one over a precipice
    c : steep rapids in a river the cataracts of the Nile
    d : downpour, flood cataracts of rain cataracts of information

I’m guessing that the medical term is used explicitly because of the “portcullis” meaning in Latin, since cataracts more or less block light from entering the eye. The Online Etymology Dictionary seems to agree, so that makes me feel better.

The medical condition

Multiple online sources (the Mayo Clinic and the American Academy of Ophthalmology to name just two) agree with the Merriam-Webster definition. Cataracts are a clouding of the lens of the eye. This can result in blurry vision, seeing double, light sensitivity, having trouble seeing well at night, needing more light when reading, seeing “halos” around lights, and seeing bright colors as faded or yellowed. They are the most common form of vision loss in people over the age of 40, and the single most common cause of blindness in the world (in the US alone, more than 22 million people have cataracts).

Aging is the most common cause of cataracts, because the proteins in the lens of your eye will denature over time. This is not a good thing, because your lens is made of living cells and denatured proteins disrupt the cells and can even kill them. Diabetes and high blood pressure can accelerate the process, as can ultraviolet light (UVB, specifically) and other radiation and blunt trauma to the eye. There is a genetic component to the development of cataracts as well, particularly if someone develops them in childhood or as young adults. These aren’t the only causes, of course. Just the most common.

The most common forms of cataracts are subcapsular, nuclear, and cortical. Subcapsular cataracts start at the back of the lens, and are most common in diabetics and people taking medical steroids. Nuclear cataracts start in the center of the lens, and are most commonly associated with aging. Cortical cataracts start at the edge of the lens and work inwards ina “spoke-like fashion”. There are also congenital cataracts, which you are born with or develop during childhood – usually due to your genes or some form of infection or trauma.

Treatment

Ultimately, the only treatment for cataracts is to remove the existing lens and replace it with an artificial lens called an intraocular lens that matches the prescription (if any) that you need for your glasses. The intraocular lenses come in a wide variety of different types, and if you need one you should consult with your ophthalmologist to see which ones make the most sense for you.

Surgery is generally considered a last resort, though. As long as the cataract symptoms aren’t bothering you, and the problems with your vision can be corrected with glasses, there generally no need to undergo surgery. Cataract surgery is considered pretty routine, but the only really risk-free surgery is one that you don’t have.

Hang on, hang on. This is all about people. Didn’t this start with a dog?

Yep. But cataracts aren’t limited to humans. It’s a condition caused by disruption and damage to the lens of the eye, so any animal with an eye with lenses can develop cataracts. There’s a lot of information on the internet about dog cataracts, and mentions of cats. One veterinarian stated that they are “the most common cause of blindness in dogs, and can also affect people or any species of animal”. Like humans, animal cataracts can develop from age, diabetes, trauma, genetics, or something called Progressive Retinal Atrophy – the name for a cluster of generic disorders that cause the retina to degenerate. Animal cataracts can be treated in the same way as human cataracts. Progressive Retinal Atrophy has no treatment, though.

Impaired vision and even blindness aren’t a death sentence for a house pet, though. Rosie gets around just fine, as long as you don’t move her food and water dishes and rearrange the furniture a whole lot. So if you live in the Cincinnati area and want to adopt an adorable little blind dog (or another animal), contact the Peppermint Pig Animal Rescue. They’ve got a lot of animals looking for a loving new home.

What Fossils Did I Find?

Way back in February, I wrote about the fossils my son found. At that time, I promised him I’d do some research and find out what kind of fossils they were. To recap, here’s what they looked like:

Time passed, and he asked other questions, and I got busy studying for a certification test at work (which is why I’ve been so quiet the past few months). But finally, since I’ve had a chance to catch my breath, it’s time to answer a question: what, exactly, are those fossils?

Well?

My primary source for this is Identification Guide for Common Fossils of the Cincinnatian. Based on this guide, most of the fossils appear to be Brachiopods, most likely some species of Cincinnetina (since they’re common in the region) – from the pictures in the guide, though, they could be Platystrophia ponderosa. The point is, they’re certainly brachiopods, and they’re around 480 to 440 million years old.

To tell you the truth, my son was disappointed that he didn’t find a Tyrannosaurus Rex.  That wouldn’t be particularly likely, however, for a few reasons.  The first being that T. Rex didn’t live 440 million years ago, and the second being that if T. Rex did live 440 million years ago in Cincinnati he would have drowned.  Because Cincinnati was under water.

Map courtesy of The Paleomap Project

So, no Tyrannosaurs here.  Certainly not in the strata that was laid down on his brachiopods.

And what, exactly, is a brachiopod?

Well, Wikipedia says that brachiopods are:

…a group of lophotrochozoan animals that have hard “valves” (shells) on the upper and lower surfaces, unlike the left and right arrangement in bivalve molluscs. Brachiopod valves are hinged at the rear end, while the front can be opened for feeding or closed for protection.

“Lophotrochozoan” animals are a clade of bilaterally symmetrical animals with cillia around their middle, if that helps.

Brachiopods are related to mollusks and annelid worms (earthworms and leeches). There are around 330 living species. There were a whole lot more of them back in the past, with the greatest diversity of Brachiopods occurring in the Devonian. The Permo-Triassic mass extinction crushed a lot of that diversity, and it has never fully recovered.

Modern brachiopods feed by sucking water in through their sides, using their cilia to trap particles of food, and then expelling the water and any waste products through the front. They absorb oxygen through their skin, and have colorless blood, and some modern species can live over 30 years (assuming they aren’t eaten).

Case closed, right?

Well, except for this strange little thing:

Uhm. What is that?

I have no idea. I’m pretty sure that’s not a brachiopod. Not unless we’ve got the shell end-on, and it also folded in a pretty dramatic fashion. After some digging, I four possible candidates. Here they are.

1. It’s just a rock. Needless to say, I find that boring. It is the null hypothesis, but I don’t think it’s accurate. after all, the color resembles that of the other fossils in the piece of stone my son found. So, although it’s certainly possible, I don’t think it’s correct.

2. It’s a piece of an Isorophus cincinnatiensis. This might be a reach, because it would make it a fragment of an arm of a 440 million year old echinoderm. Pros for the argument are that it’s from the region, it’s about the right size, and it looks kind of like the arm seen in this picture. Cons for the argument include the fact that it doesn’t look a whole lot like the arm in that picture.

3. It’s a bit of coral. I couldn’t find any pictures of coral that curves like that, but that doesn’t mean they don’t exist.

4. It’s something I can’t identify. Yes, yes, that’s an utterly lame hypothesis. But I’ve got nothing else, and I’m pretty sure it’s some flavor of fossil. So, I’ll probably just leave it at that. Unless someone reading this happens to know what that might be.

Why Do Birds Poop And Pee At The Same Time?

I don’t know if my son was watching a nature program, or if he’d been talking about this at school, or what. All I know is that, as we were walking into the condo one day, he suddenly stops and points. “Look dad! An owl!”

I stare along the side of the building, wondering which of the trees he’s talking about. Or is it perched on a balcony, maybe? “I… don’t see it,” I say.

“It’s right there!” he exclaims, pointing. “Oh, no. It’s a squirrel. Look, dad! A squirrel!”

“I don’t see it,” I tell him. “But my eyes aren’t as good as yours.”

He nods at that. “Dad?”

“Yes, son?”

“Why do birds poop and pee at the same time?”

…that is not what I thought he was going to ask.

Do they poop and pee at the same time?

This seems like the first place to start, because I’m not at all certain they do. I mean, sure. I’ve heard this before. But it wouldn’t be the first time I’ve found that “received wisdom” is wrong and that something I thought was true wasn’t true. However, in this case, it seems that received wisdom is correct.

This is going to be more than I wanted to know, isn’t it?

Hey, you’re the one reading this.

Pretty much all animals produce ammonia (NH3) during digestion. It’s a side effect of the breakdown of proteins, which all animals need whether they’re carnivores or herbivores. Ammonia is, however, toxic (doses of 350 mg/kg of weight can kill), which means that animals have to deal with it in some fashion. And by “deal with” I mean “get rid of”.

Generally speaking, mammals will mix it with some of the waste carbon dioxide (CO2) they produce through breathing and convert it into urea (CO(NH3)2) – a far less toxic chemical (the lethal dose is 8,471 mg/kg) that also happens to be water soluble. Mammals then, generally speaking, expel it (along with other waste chemicals) in the form of urine.

Birds don’t do this. Birds, it seems, don’t even have bladders.

Sigh. Tell me more.

To start with, most birds convert ammonia into uric acid (C5H4N3O3, lethal dose around 5040 mg/kg) instead of urea. The other thing they do, which is the reason why they simultaneously poop and pee, has to do with anatomy. See, bird excretory systems work a lot like lizards. They have kidneys, of course, and ureters (the ducts that allow urine to leave the kidney). However, they lack bladders. Instead, they have something called a cloaca – a multipurpose organ that serves as both the reproductive and excretory organ.

The urine enters the cloaca through the ureters, where it is pushed up into the large intestine. The large intestine re-absorbs much of the water content, allowing the urine to be concentrated into a thick paste before it is passed by the bird. since uric acid dries white, this lends bird droppings their distinctive appearances.

So, in short, birds poop and pee at the same time because of evolution.  And because they aren’t equipped to poop and pee separately.

Why Do Sharks Eat So Many People?

“Dad?” my son asked as we got out of the car. “Why do sharks eat so many people?”

I assume he’d seen something about sharks at school, but the question still came out of nowhere. Thirty seconds before, he’d been telling me about his school’s Mardi Gras party and asking me if I felt better (because I’ve been sick, which is why this article still isn’t looking at the fossils he found). So, I put my mind to it. “I don’t think they do,” I answer.

“They don’t eat people?” he responds, sounding skeptical.

“Well, they can,” I concede. “But they don’t eat people all that often.”

“Why not?” he asks, and I swear he sounds disappointed.

“Well, a lot of them are kind of small. And we aren’t the kind of things they normally hunt.” I’m trying to remember shark facts, now. “Most of them are probably just wondering what we are, and people get scared of them and think they’re attacking.”

“Why do people get scared?” he asks.

I shrug. “Why did you get scared of them, when we went to the aquariam?”

“Because they look mean!” Then he grabs my hand. “Since you’re not feeling good, can we take a break and play Star Wars?”

Do sharks eat a lot of people?

This is one of those questions where I really hope I told my son the right thing, because I was working from half-remembered articles I’d read years ago, and memory is a fickle, tricky thing. Fortunately, it turns out that the University of Florida maintains the International Shark Attack File (ISAF), which they describe as “the longest running database on shark attacks, has a long-term scientifically documented database containing information on all known shark attacks, and is the only globally-comprehensive, scientific shark attack database in the world”.

Before we dive into the numbers, though, it’ll be important to define two terms the ISAF uses: provoked attacks and unprovoked attacks.

  • An unprovoked attack is edfined as “incidents where an attack on a live human occurs in the shark’s natural habitat with no human provocation of the shark.”
  • A provoked attack, on the other hand, usually occurs “when a human initiates physical contact with a shark, e.g. a diver bitten after grabbing a shark, attacks on spearfishers and those feeding sharks, bites occurring while unhooking or removing a shark from a fishing net, etc.”

The ISAF reports that 2016 was a pretty typical year, with a total of 150 alleged shark attacks. Out of those 150 attacks, here’s how the results broke out:

  • 81 were classified as unprovoked attacks (53 total in the United States, 43 of which were in Hawaii).
  • 37 were classified as provoked attacks.
  • 12 were sharks biting boats (aka “boat attacks”).
  • 1 was a shark eating part of an already dead human cadaver.
  • 12 had insufficient evidence to prove a shark attack.
  • 7 were determined to be attacks by other marine animals (including a barracuda and an eel).
  • 5 were determined to be abiotic injuries (that is, an environmental injury – scraping coral or rock, for instance).

So, in the fairly typical year of 2016, there were 118 total shark attacks on humans (131 if you count the boat attacks and the scavenging). 2015, by contract, hit 98 unprovoked shark attacks- the highest yearly total on record. On average, shark attacks result in 6 to 8 fatalities per year (depending on what period of time you average out), but 2016 only had 4 shark attack fatalities. Statistically, surfers are most likely to be attacked 958% of the total), followed by recreational swimmers and waders (32.1% of the attacks).

That’s not a lot of attacks, is it?

No, not really. In fact, there’s a whole lot of animals that are much more likely to kill you. According to the BBC, venomous snakes kill an estimated 50,000 people each year, rabid dogs kill an average 25,000 people each year, crocodiles kill an estimated 1,000 humans per year, and hippos kills an estimated 500 people per year. All of which makes the paltry 6-8 shark kills each year pretty tame.

friendly-shark

Still, it’s probably best not to do this unless you know what you’re doing.

The ISAF provides some other interesting comparisons. The odds of dying from a shark attack are 1 in 3,748,067. Fireworks are about 11 times more lethal (odds of death: 1 in 340,733), sun and heat exposure are 273 times more lethal (odds of death: 1 in 13,729), and the flu is 59,664 times more likely to kill you (odds of death: 1 in 63).

Why do shark attacks get so much attention, then?

Rarity, in my opinion. Rarity and shock/

See, we notice things that appear out of the ordinary. According to the CDC, heart disease is the leading cause of death in the United States (614,348 deaths in 2014), followed by chronic lower respiratory diseases (147,101 deaths), accidents (136,053 deaths), stroke (133,103 deaths), Alzheimer’s disease (93,541 deaths), diabetes (76,488 deaths), and influenza and pneumonia (55,227 deaths). Most of those get no attention at all, unless they’re really spectacular or they happen to someone famous. But death by animal attack? That’s unusual, particularly in the United States. And particularly because we like to think we’re outside the food chain. Homo sapiens sapiens is, realistically, the ultimate alpha predator and one of the dominant environmental forces on the planet. It’s unsettling to be reminded that we’re still animals, and that we can still become prey.

Also, sharks inhabit an alien environment that we can only meaningfully visit with the benefit of technology. A wolf or bear attack happens on dry land, so the surroundings aren’t inherently hostile to us. But sharks? A shark could kill us with their own environment, even if the bite isn’t fatal. So, they seem frightening.

Just in case I am one of the unlucky ones, any tips?

Actually, yes. Here’s what the ISAF says: “If one is attacked by a shark, we advise a proactive response. Hitting a shark on the nose, ideally with an inanimate object, usually results in the shark temporarily curtailing its attack. One should try to get out of the water at this time. If this is not possible, repeated blows to the snout may offer a temporary reprieve, but the result is likely to become increasingly less effective. If a shark actually bites, we suggest clawing at its eyes and gill openings, two sensitive areas. One should not act passively if under attack as sharks respect size and power. “

How Many Spiders?

I’ve been sick for a few days now, so I haven’t put any real time into the “what are these fossils” article I promised last time. Instead, let’s look at something comparatively simple. I picked up my son from Kindergarten yesterday. Normally, since I was home and it’s only about a quarter mile, we’d have walked. But, like I said, I’ve been sick. So he’s in the back seat excitedly telling me about his Valentine’s Day party. “Dad?” he asks as we pull into our garage.

“Yes, son?” I respond.

“How many spiders can you carry?”

No, I have no idea where that came from. But I’ve gotten used to that by now. “Well,” I say, “that depends on how big they are, and how cooperative they are.”

So, how many could you carry?

“I could carry a hundred spiders!” he declares.

“Maybe,” I tell him. “If you could put them in a box. Or if they were tiny and well-trained.”

So, how many could you carry? Like I said, it depends on the spider. The good people at Guinness World Records say the Patu marplesi is the smallest spider, while Wikipedia contradicts them and states that a related species – the Patu digua is the smallest. Either way, it’s a tiny spider – the body size is only 0.37 mm – and the author of Catalog of Organisms states that “If one of these spiders crawled into your ear while you were sleeping, it could probably slip into your Eustachian tubes and tap on the back of your eyeballs.” So try not to think too hard about that.

patu-digua

“Peek-a-boo!”

I couldn’t find anything at all about how much (little?) this critter weighs. So, I’m going to run the risk of estimating. Here’s what I did, so that you can play the home game. I found an article titled “Estimating Live Spider Weight Using Preserved Specimens” from The Journal of Arachnology in 1996. It provides a formula for calculating weight from length for spiders: ln weight = 1.844 + 2.711(ln length), and seems to indicate that the weight is read in milligrams (mg) and the length in millimeters (mm). So, that would give us ln weight = -1.844 + 2.711(ln 0.37). That works out to… let’s see…

  1. ln weight = -1.844 + 2.711(ln 0.37)
  2. ln weight = -1.844 + -2.695
  3. ln weight = -4.539
  4. e^ln weight = e^-4.539
  5. weight = 0.010684 mg

So, one 0.37 mm spider appears to weigh 0.01 mg. How many of these could we move? Let’s find out?

Bare Hands

My palm is, roughly speaking, a 9 cm by 9 cm (90 mm by 90 mm) square. That gives me 8,100 mm of surface area, so I could stack a single layer of 8,100/0.37 = 21,891 well behaved Patu digua on one hand. Using both hands, I could carry 43,782 of them. The two-hand load would come out to 0.43782 grams, or 0.0015 ounces of spider.

Let’s try and do more. If I cup my hands, I get a sort of rounded cone that’s 7 cm (70 mm) in diameter by 7 cm (70 mm) deep. That gives me a volume of 359,189 cubic mm. Now, let’s assume that the Patu digua takes up the same volume as a sphere 0.37 mm in diameter. That’s 0.212175 cubic mm. So, in my cupped hands, I could carry 359,189/0.212175 = 1,692,890 Patu digua. Those guys would weigh in at 18.0868 grams (0.63799 ounces).

We’re not savages, you know

Yes, I know. So let’s fill a box. A standard U-Haul shipping box is 41.5″ (1054.1 mm) x 38.5″ (977.9 mm) x 18.75″ (476.25), for a volume of 429,072,327.3375 cubic mm. That means I could carry 429,072,327.3375/0.212175 = 202,256,756 of the little spiders – 21.606 kg (47.6 pounds) of Patu digua. My son weighs more than that, so I know for a fact that I could easily carry that box of spiders from my house to my car, and then from the car to the Post Office, and then from the Post Office back to my car because the USPS would most likely refuse to accept that package.

Cool. What about big spiders?

National Geographic informs me that the South African Goliath Birdeater Tarantula is the biggest spider in the world as measured by body size. Nothing I could find gave me an explicit size, but terms like “puppy sized” and “the size of a dinner plate” were bandied about with distressing familiarity. National Geographic also states that:

Many of the locals in northeastern South America regard T. blondi as a tasty snack. They first singe off the urticating hairs, then wrap the spider in banana leaves to roast it. Tarantula expert Rick West, who once sat down for a meal of these spiders with the local Piaroa people of Amazonas in Venezuela, says T. blondi can be surprisingly tasty and moist. (Also see “UN Urges Eating Insects; 8 Popular Bugs to Try.”)

“The white muscle ‘meat’ tastes like smoky prawns, while the gooey abdominal contents is hard-boiled in a rolled leaf and tastes gritty and bitter,” West says. “The three-quarter-inch [two-centimeter] fangs are used after the meal as toothpicks to remove T. blondi exocuticle from between one’s teeth.”

goliath

“I’m tasty!”

On the other hand, if you’re measuring by legspan the prize goes to the giant huntsman spider, with a leg span over one foot (30.48 cm) across. No word on how they taste, though.

huntsman

“Come on and have a go, if you think you’re hard enough!”

Without specifics, I can’t tell you how many I could handle. One per hand, maybe, and maybe four in a shipping crate. But, on the other hand?  Oh my god no.

Who Was The First Person?

That was the question my son asked, from the back seat of my wife’s car. I don’t remember the context, but I think we were talking about his grandparents. Things my dad had done, things my wife’s father had done, sharing family stories. That sort of thing. And then he asked it. “Who was the first person?”

That is a hard, heavy question.

What is a “person”?

Merriam-Webster gives multiple definitions for the word “person”:

  1. human, individual —sometimes used in combination especially by those who prefer to avoid man in compounds applicable to both sexes <chairperson> <spokesperson>
  2. a character or part in or as if in a play : guise
  3. a : one of the three modes of being in the Trinitarian Godhead as understood by Christians; b : the unitary personality of Christ that unites the divine and human natures
  4. a archaic : bodily appearance; b : the body of a human being; also : the body and clothing <unlawful search of the person>
  5. the personality of a human being : self
  6. one (as a human being, a partnership, or a corporation) that is recognized by law as the subject of rights and duties
  7. reference of a segment of discourse to the speaker, to one spoken to, or to one spoken of as indicated by means of certain pronouns or in many languages by verb inflection

For these purposes, we’ll focus on the first definition: “human, individual”. Which shouldn’t be a surprise, as it’s pretty clear from the context that my son’s question should be understood as “who was the first human”.

Human beings are formally known Homo sapiens, with contemporary human beings classified in the subspecies Homo sapiens sapiens – a rather arrogant sounding name, since it means “Wise wise man” when translated from Latin. We are part of family Hominidae (also known as “great apes”), a family that includes Homo (us), Pongo (orangutans), Gorilla (gorillas, go figure), and Pan (chimpanzees). Hominidae is part of the Primates, which is an order of the class Mammalia. At present we are, arguably, the most successful branch of both Primates and Hominidae, as we have a globe-spanning range of habitation. We’re certainly the most successful current branch of Homo, as we’re the only extant branch of that genus.

primate-cladogram-2_med

Our family tree

So, who was the first Homo sapiens?

This is where things get tricky, because “species” is a difficult concept to pin down. You’re probably familiar with some version of Mayr’s Biological Species Concept, which defines a species as “groups of actually or potentially interbreeding natural populations, which are reproductively isolated from other such groups”. The problem with this definition, and this is a problem biologists are well aware of, is that nature is “squishy”. Not all species reproduce sexually, for instance. Does that mean they aren’t a species because this concept doesn’t apply? If two different species can successfully breed, even if they wouldn’t normally do so in the wild, does that make them different speices because they’re usually reproductively isolated or does it make them the same species because they can still produce viable offspring? The answer is the subject of a lot of arguments among biologists.

This “squishiness” combines with evolution to make it impossible to pin down a “first” Homo sapiens, or even to say for certain what was H. sapiens and what was a different Homo species. The Neanderthals, for instance, were Homo neanderthalensis, a different species from Homo sapiens, but there is enough genetic evidence to make an argument that they certainly weren’t reproductively isolated from our species. The jury is still out on that, but given some of the other things humans will do today it’s certainly not unreasonable to assume that our ancient ancestors were open to having sex with another species of Homo.

All we can say for certain is that our species differentiated itself from our direct ancestor species – Homo erectus (“upright man” – somewhere between 1.8 million years ago and 200,000 years ago. Which means that we likely overlapped with H. erectus for a significant amount of time, as the oldest fossils of H. erectus are around 1.9 million years old and the youngest are around 70,000 years old. So, worst case, we overlapped with H. erectus by some 130,000 years, which is significantly longer than recorded human history. But we can certainly speculate. There wouldn’t have been a sharp dividing line between H. erectus and H. sapiens, and certainly no moment where a H. erectus mother looked at her baby and said something like “hey, this is different“, because evolution doesn’t work like that.

The lineage that gave rise to H. sapiens would likely just have started off as just another subspecies of H. erectus, like H. erectus erectus (“Java man”), H. erectus nankinensis (“Nanjinj man”) or H. erectus georgicus. That subspecies would have been somewhat geographically and/or culturally isolated from its neighbors – although possibly still indulging in the occasional opportunistic “gene swapping opportunity” – until, over time, it became different enough that it became a distinct organism. Could the new archaic H. sapiens have successfully interbred with H. erectus at that point? Possibly. We could have interbred with H. neanderthalensis, after all. But since all we have left of H. erectus is fossil bones, we’ll probably never know for sure.

That said, genetic studies have indicated that there is something approximating a “first” human man and a “first” human woman.

It’s fun to stay at the MRCA!

MRCA is the Most Recent Common Ancestor, and it’s exactly what it sounds like: the most recent individual from which all members of a set group are descended. For you and your siblings (if you have any), your MRCA is your father and mother. For you and all of your cousins on your mother’s side of the family, your MRCA is your maternal grandparents. And so on. Generally speaking, the larger the group the further back you have to go to get a MRCA. Also, the paternal and maternal MRCA need not always have lived at the same time. Imagine yourself as having a half-brother because one of your parents divorced and remarried. YOu might share a father with the half-brother, making your father the paternal MRCA for that group. But you might have to go back dozens of generations to find a maternal MRCA.

The maternal MRCA for all of H. sapiens is nicknamed the Mitochondrial Eve, and she lived in Africa quite some time ago. How long? well, depending on the type of analysis applied, it could be as long ago as 234,000 years ago or as recently as 99,000 years ago. I won’t pretend to understand the details of how that was calculated, beyond the simple statement that it has to do with mutation rates in mitochondrial DNA – the DNA of the little organelles that our cells use to convert oxygen and sugar into energy. I’m a stockbroker, after all. Not a geneticist or cell biologist.

Our paternal MRCA has been nicknames the Y-chromosomal Adam, and is currently estimated to have lived around 200,000 years ago. Also in Africa, so there is a slim possibility that our paternal and maternal MRCAs knew each other. Don’t count on it, though.

Why Are They Called Theropods?

Every night, before he goes to bed, my wife and I read a book to my son.  Last night, he picked out one of the books he got from the library.  I don’t recall the title, but it was full of cartoon dinosaurs accompanied by facts about them.  A lot of those facts were things I’ve learned in a lifetime of obsession with the “terrible lizards”, and a good number of them are things he’s learned from Dinosaur Train and from other books we’ve read.  But that really isn’t the point of the evening ritual.  If he learns something, that’s great.  For me, though, it’s the opportunity to read to him.

“What’s a theropod?” my son asks.

“It’s a type of dinosaur,” I say, realizing that I’ve forgotten what a theropod is or what the other type of dinosaur is.

“Why is it called a theropod?” he continues.

“I don’t know,” I tell him.

“Can you find out?”

Of course I can.

Dinosaurs!

Let’s start off with the basics.  You may have heard that dinosaurs aren’t reptiles.  This is not strictly true, as Dinosauria is a clade of the class Reptilia – a class that in modern times includes turtles, crocodilians, snakes, amphisbaenians (aka worm lizards), lizards, and tuatara.  Dinosauria contains two Orders, Ornithischia (primarily herbivorous dinosaurs with a hip structure similar to birds) and Saurischia (primarily carnivorous dinosaurs with a hip structure similar to lizards), although it appears that many contemporary paleontologists classify Ornithischia and Saurischia as clades rather than orders.

Clades?

A clade can be thought of as a branch on the tree of life.

tree-of-life_2000

More specifically, a clade consists of a single ancestor species and all the species that evolved from it.  In broad strokes, all life is a clade because everything traces back to a single organism.

Theropods?

“Theropod” derives from Greek, and means “wild beast foot”, and was coined in 1881 by O. C. Marsh as a suborder to hold Allosaurus.  They are ancestrally bipedal, ancestrally carnivorous dinosaurs – “ancestrally”, because some species of theropods evolved omnivorous or herbivorous diets, or quadrupedal gaits, or both.  Depending on the “age” of the species and the specific lineage they may have had scales or feathers or both.  The order includes many of the famous, “sexy” dinosaurs, such as the Tyrannosaurus Rex, the “four-winged” Microraptor, and chickens.

Chickens?

Yes, chickens.  See, one clade within Theropoda was Averostra (“bird snouts”), and Averostra had a couple of clades survive the Cretaceous–Paleogene extinction event:  Ceratosauria and Orionides.  Within Orionides was the clade Maniraptoriformes, which was the parent clade for Avialae, which was the parent clade for Aves – modern birds.  So, yes, birds are “lizard-hipped” dinosaurs.  Go figure.

dinosaurs