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Home , Fowl

Are We Not ?

A STORY OF DARWIN, EVO- DEVO, AND THE OUROBOROS OF AVIAN GENEALOGY

By Arielle Johnson Illustrations by Cristina Daura

CHICKEN 33 THE CHICKENING of , at which he was especially found, naturalists were increasingly able to OF successful (one of his breeds, the Sebright correlate depth to successive periods While another variety of —the finch— Bantam, is still around today). In his mus- in time and refine the relationship between famously spurred Charles Darwin to for- ings on “The Art of Improving the Breeds of and living organisms. mulate the theory of evolution, his think- Domestic ” we can see some famil- The discovery and study of ing about selection (natural, artificial, sex- iar concepts shaping up, like sexual selec- fossils really took of around the turn of the ual, or otherwise), survival, and fitness, tion (“The greatest number of females, will, 19th century, and how these changes accumulated in of course, fall to the share of the most vigor- and it quickly organisms over time and generations was ous males”), selection by farmers being became clear As anyone who got their dino-science from helped on its way by the . Having echoed in “selection” by natural that at some returned to England in 1836 with trunk conditions, and the survival of point in the past, the Dr. Alan Grant knows, before there were loads of samples in tow from a 5- stint the fittest. world was domi- as the on-board gentleman-naturalist of Reading this in 1838, nated by gigantic chickens (or chicken ), there were dino- the HMS Beagle during its voyages in and Darwin mused that the reptiles that had saurs. And no bird is more closely related—on around South America, the then-27-year- “whole art of making vari- since totally dis- old Darwin made a name for himself dis- eties may be inferred from appeared. Dar- a genetic level—to the attractions at Park playing impressive fossils from extinct facts stated [by Sebright]”; win himself had South American mammals and writing and with these facts in mind, used mammal fos- than Gallus gallus domesticus, or chickens (and, fne, papers on geology. he rapidly developed the fun- sils from South Amer- Oddly for someone who has cast such damental points of the theory of ica—extinct giant sloths turkeys, too). Of the roughly 10,000+ modern spe- a long shadow on biology, his training was, evolution over the rest of the year. He’d and armadillos— in develop- mostly, in geology. While Darwin brought take another 20 developing the finer ing the basic arc of the theory of evolution. cies of , the chicken is by far the most populous and back a large number of taxidermied bird points and to actually publish On the Origin With dinosaurs, a big question remained— husbanded. At any given point, there are about 20 billion samples, he wasn’t much of an ornitholo- of Species (he got interrupted by orchids how did we get from giant reptiles to the gist. He was, however, able to map where and barnacles), but we wouldn’t be talking animals we have today? The connection chickens on the planet, and these birds have undergone the he’d collected every one of the numer- about the evolution of the chicken now, had between dead giant sloths and living, reg- ous finches he brought back with him, the handy chicken not helped develop the ular-sized sloths was obvious enough. But fewest genomic changes overall of any bird species, refect- and to figure out that each species, which theory of evolution in the first place. if scientists went back far enough in the had similar bodies but huge diferences record and found dinosaurs but no birds ing slower evolution from dinosaurs and, cumulatively, less in shape, was naturally confined to DINOSAURS AND BIRDS: or mammals, and evolution was true, then evolution overall. its own semi-isolated island. Pondering THE URVOGEL GREAT MOMENTS IN WTF happened? this geographical-morphological relation- THE HISTORY OF COINCIDENCES When Darwin released On the Ori- So how did we get from T-Rexes to ship—that the species were related to each gin of Species in 1859, he recognized other, but each adapted to their own spe- At the same time as Darwin was writing, that an obvious consequence of evolu- the beady-eyed, massive-breasted, cific locality—as well as other phenomena debate about a fundamental evolutionary tion was that “if species have descended he’d uncovered sent him down a rabbit hole link—between dinosaurs and birds—was from other species by insensibly fine gra- -pumping creatures of today? of theorizing and background brewing. Fossils had been dations, do we not everywhere see innu- research further afield. known and described merable transitional forms?”. He explained Darwin began working since ancient times, that the lack of obvious living transitional out ideas on transmu- and Creationists were forms was probably because tation of one species fans of attributing any evolved species replaced into another, descent, unusual findings as evi- their original lineages, and adaptation, and when dence of Noah’s deluge. and hedged that tran- natural history could only take Petrified oysters found way sitional fossils weren’t him so far, looked for inspiration in works on inland? Biblical flood. Skeletons of creatures being found “embed- breeding and husbandry. He found that aren’t around anymore? Missed the ark. ded in countless it in the writing of Sir John Sebright, a pol- But as critical thinkers poked holes in these numbers in the crust itician, agricultural innovator, and breeder arguments, and more and more fossils were of the earth” because

34 LUCKY PEACH CHICKEN 35 fossils are really hard to make and in the it turns out, is another of Darwin’s great took up the debate: were the “endless otchi-in-2001 prices. This gave Darwin stretches of time and across wide spaces grand scheme of things, only happen very gifts to chickenology. Hearkening back to forms most beautiful” that fanciers saw, access to specimens and data that would in geography. Intensive studies of the rarely. “The crust of the earth is a vast his earlier inspiration from the chicken and and that we can still see today, in the not have been available to a similarly-ed- genetic sequences of modern chickens, museum,” guys, “but the natural collec- other domestic animals, post-“On the Origin many breeds that make up the species ucated Naturalist of a generation or two ancient chicken bones, and various wild tions have been made only at intervals of of Species” and pre-“Descent of Man”, Dar- Gallus gallus domesticus—the Bantams, before. In addition to extensive com- jungle , especially considered in tan- time immensely remote”, so chill out with win made a deeper exploration into artificial the gamecocks, the Malays, the Cochin, parisons of appearance and analysis of dem with archaeological, linguistic, and the transitional fossil demands. selection called “The Variation of Animals the Dorking, the Spanish, the Creepers, reported data from chicken and jungle historical evidence, have enriched, compli- Then, 2 years later, a new find gave and Plants Under ”, where the Guelderlands, the Crested, the Silkies, fowl observers in Asia (the aforemen- cated, and sometimes muddied the picture naturalists a frisson of excitement he fleshed out the argument for the Red the Frizzled, the Rumpless, and others— tioned educated white dudes), he also of where and when the jungle fowl became and vindication. Jungle Fowl as the progenitor of the the result of many diferent ancestors? Or, approached the question empirically, the chicken. In a limestone quarry in Bavaria, a dino- modern chicken. could they all come from just one? (He set through breeding experiments. Genetic studies suggest that a key fea- saur-ish fossil German naturalists called Carolus Linnaeus, the father of modern aside the still-popular idea that all were He was happy to report that, of the ture of most modern chickens—their yel- the Urvogel (“first bird”), and later became , was perhaps the first Western separate products of Intelligent Design) wild jungle fowl species in Asia, the evi- lowish skin—could not have come from known as the (“Ancient naturalist to classify the chicken as a rela- At the time Darwin was pondering dence showed that only Red Jungle Fowl red jungle fowl, which have whitish skin. wing”) was excavated. It was roughly the tive of the red jungle fowl. Technically, the this, natural habitats for the contenders could produce non-sterile ofspring with The gene that makes pigments from the size of the raven and had, like most dino- domestic chicken is classed as a subspe- for chicken-ancestry lay very neatly in chickens (a phenomenon that’s currently chicken’s diet show up as color in the skin saurs, a long tail, a jaw full of teeth, and a cies (Gallus gallus domesticus) of the red the areas under British interest for colo- edging the red jungle fowl towards extinc- doesn’t exist in red , but does flat sternum. It also had a wishbone, some jungle fowl (Gallus gallus) and a relative of nization, which was in its heady oppres- tion as a distinct species—rather than in grey jungle fowl, a chicken parentage hollow bones, downy all over its other Gallus species, all of which are difer- sive heyday in the mid-19th century. This dying out, it interbreeds so much with that Darwin had ruled out. Bone analysis body, and wings covered in asymmetrical ent kinds of jungle fowl. Linnaeus wasn’t meant that there were a lot of educated domestic chickens that it’s become tricky suggested that the word, therefore also from a site in northern China suggests that flight feathers. In other words, it was an advancing an argument about ances- white dudes around who, like Darwin on to find a red jungle fowl with only wild the bird, may have originated in Malay- domesticated chickens were found much obvious transitional link between dinosaurs try—evolution was not really a thing in the Beagle, were interested in dabbling in genetics), this unique interbreeding abil- sia or Java; and that recently-translated further north (in a climate where no jungle and birds. Darwin’s buddy Hugh Falconer, the 1700s, and most natural philosophers Naturalism, collecting samples of exotic ity edging it up as the most likely ancestor. ancient Chinese texts recorded chickens fowl now live), and of much earlier origin who’d seen the fossil when it was presented (what we called scientists in the early native fauna and sending specimens and Putting his chicken-fancying-specimens being imported into China in the 1400s BC. (as early as 7-10,00 years ago, or, 5-8000 at the British Museum in 1863 (Darwin was Enlightenment, when we were still invent- exacting reports back to England. Coloni- to work, Darwin intentionally made cross- (Darwin also cited the Bible as evidence, BC), than anyone expected. Was this the a recluse, so stayed home), wrote him thus: ing the idea of science) were creationists. alism and the Industrial Revolution were ings by breeding a purebred black Spanish since chickens are mentioned in the New product of an earlier original domestica- “Had the Solenhofen quarries been commis- Their goal was to catalog the animals God combining to create faster and cheaper cock with a harem of hens, most of which Testament but not in the Old). tion event, outside the current range of the sioned—by august command—to turn out a created in Genesis and their relationships transport (via the clipper ship) between were white or black and white, and none The continued professionalization of red jungle fowl, that then spread south- strange being a la Darwin—it could not have (“God created, Linnaeus organized” is Britain and its Empire than had ever of which had shown in their breed lines the gentlemanly pursuit of antiquarian- wards? Or was the chicken domesticated executed the behest more handsomely— one of his famous humble- existed before, which, in 1842, brought a the characteristic red/orange-shouldered, ism into the social science of archaeology multiple times in parallel? (Or, as has been than with the Archaeopteryx” brags)—to Linnaeus, obvi- gift of huge Chinese Cochin chickens to black-breasted, diagonally-tail-plumed fleshed out the early history of the spread suggested in critical follow-ups, mitochon- It took another century-plus for the sci- ously God had created the young Queen Victoria. Their arrival looks of the red jungle fowl. Despite their and diferentiation of the chicken through- drial DNA confirmation aside, could the entific community to finally agree, but even- both the chicken and set of a Tulip Fever-esque bubble of achromatic parentage, many of the result- out the ancient world. But after Darwin bones have been misidentified? It’s hap- tually the idea that birds evolved from dino- the jungle fowl, chicken fancy- ing chicks grew up to have orange and the debate over the primary origin of the pened, more than once, before.) As of now, saurs made its way into high school science and made ing that burst in red hackles and shoulders and dark bod- chicken stalled until the 1990’s when the the jury is still out. classes everywhere. Except Kentucky. them able the mid-1850’s, leav- ies—reverting to ancestral characteristics, rapid development of

to breed; ing a lot of exotic chickens according to Darwin. molecular biology and Darwin himself didn’t know exactly what the mechanism for evolution was—he THE UR- CHICKEN, OR, thus, they and hybrids hanging out Rounding out his breeding experi- molecular genetics, certainly didn’t know about genes, with genetics not really established as a sci- THANKS AGAIN, DARWIN were both Gal- in England, and availa- ments and ornithological analysis, Dar- fields in which precise ence until the early days of the 20th century; or DNA, which wasn’t understood lus gallus. ble for tamag- win also drew creatively on scholarship chemical analysis of to be the storage molecule for genetic information until the 1940’s. Now we know that evolution is driven by random mutation at the molecular level of DNA—if the It’s now widely accepted that the Dar- from the humanities as a record of evi- invisible components mutation hurts the organism’s fitness or sexual attractiveness (which is what usually chicken is (mostly) descended from a bird win dence that was no longer tangible: that of life—like DNA and happens), that organism doesn’t reproduce, doesn’t pass the mutation onto its called the Red Jungle fowl, which looks like the Greeks called chickens “Persian,” but proteins—allowed sci- children, does not collect $200, and the mutation dies out. If the mutation helps the bug-eyed, wily, cousin of the birds we since no chicken-like wild birds had a nat- entists to make con- with its adaptation to its environment, or makes it sexier to its prospective mates— then the mutation is passed on. So, a lot of the differences in purebred heirloom see at , and which has a natural range ural range that included Persia, they prob- nections and tell new chickens come from random mutations that humans decided to propagate. When in south and southeast Asia, from northern ably came to Greece from somewhere fur- stories about the rela- heirlooms are bred together, the new gets genetics from its parents each India in Tamil Nadu south to Malaysia, the ther east via Persia; that the etymology tionships between with different alterations to the original, red jungle fowl-like genome. Philippines, and Indonesia. This connection, of words for chickens in Asian languages organisms over long

36 LUCKY PEACH CHICKEN 37 for chicken breeders of all on grain-based chicken feed, they roamed in China, and covered in primitive downy BETTER LIVING THROUGH stripes—young, old, pro- around outside and could eat grasses, feathers), quill knobs found on T. Rex and ( ARTIFICIAL SELECTION AND) fessional, amateur—to sub- insects, grubs, and other miscellaneous Velociraptors, and wing and tail segments CHEMISTRY mit for consideration their sources of food to round out their diets. encased in amber, show that non-avian attempt to create a bird Chicken farmers actually had to let their theropod dinosaurs (so, cousins to ancient From Sebright’s bantams into that, in 12 weeks and on animals forage—if they didn’t, they got birds, though not actually birds) commonly chicken fancy, Darwin’s breeding the least possible food, metabolic diseases (similar to beriberi and had feathers, suggesting that feathers experiments, and beyond, artificial created the largest, most anemia in humans) from missing the micro- evolved before birds did. selection accelerated the evolution of breasty, picture-perfect nutrients they would usually get from their And while we haven’t been able to the chicken in the 19th and early 20th specimen. The win- grub supplements. isolate dinosaur DNA yet (sorry, Juras- centuries. Around this time, there ning chickens This brings us to the third element of sic Park fans), we’ve learned a lot about was interest in “improvement” were an hybrid, the commercial chicken trifecta: the “vital what genetic changes are necessary to of breeds to make them grow the first generation essences” or vitamins and minerals discov- make changes in an animal’s shape. larger, faster, more eficiently, of a cross between ered in the early part of the 20th century, in mind that dinosaurs, like chickens and or lay more eggs, and rearing a Red New Hamp- the molecular characterization of the com- humans, have a skull with two eyes, a rib- flocks specifically for egg shire Hen and a pounds responsible for limes being able cage, a pelvis, a spine, and forelimbs and laying became common California Cor- to cure scurvy (vitamin C), and brown rice hindlimbs. They have a tail where a chicken (with the male chicks nish Rooster. curing beriberi (vitamin B1), among oth- has a stumpy structure called a pygostyle, a in these flocks used as At 12 weeks, ers. With these isolated micronutrients in jaw and teeth where a chicken has a beak, “broilers” or meat chickens), especially they weighed hand, chicken farmers could fortify inex- and their 5-fingered front limbs difer from after the first world war. But that was pea- 3.75 pounds each; this was an improvement pensive corn, and create a feed that fat- a chicken’s 3-appendaged wings, though nuts compared to the ways chickens have compared to the average chicken of 1943, tened chickens quickly without killing those wings develop in the chicken embryo been changed in the decades since World which at 12 weeks weighed only 3 pounds. them. This allowed producers to go from from hand-like structures. War II. Part of their success came from a phenom- 50-200-chicken flocks to facilities with But the basic map of a vertebrate isn’t Chickens have, over successive gen- enon called heterosis or hybrid vigor, which thousands upon thousands of chickens, revised wholesale when something like erations of selective breeding, been trans- is the tendency of the ofspring of two par- since there was no longer any need to let a bird emerges from the lineage of dino- formed from a variety of heirloom breeds ents, each from a diferent inbred or heir- chickens out onto pasture to keep them saurs. We’ve learned from a new branch of that gave both eggs and meat into an indus- loom line, to have biological enhancements alive. science called evolutionary developmen- trial bioreactor for turning corn into pro- (like size, strength, or uniformity) compared And just like that, you’ve got a recipe tal biology (or evo-devo) that the evolved tein as eficiently as possible. to their parents. for billions of giant, inexpensive, tasteless changes in the anatomy of an adult organ- With these chickens, you The selective breeding continued over chickens, with no GMOs necessary. ism are generally laid out as it develops can choose eggs or subsequent years, expanded from grocery from a single-celled zygote through its meat, not chains to university animal science depart- CHICKENS OF FUTURE PAST embryonic phase into a baby animal. This both. And ments and commercial chicken breeders, development isn’t directly guided by a gene you certainly and by 1973, chickens destined to become And as for chickens and dinosaurs, that codes for a tail or a beak, per se, but don’t get to choose meat were reaching maturity at 8.5 weeks. we’ve barely gotten started. We know (because nothing in nature is ever simple) flavor. That’ll be $7. It’s now possible to rear chicks that reach that as the saurischian class of dinosaurs from feedback between genes called HOX The infa- maturity even faster, in 5 weeks, and put on evolved throughout the Trias- genes, other genes that produce enzymes mous Chicken of 4 pounds and change in that time. sic and into the Juras- that start and stop growth, and genes that Tomorrow contest of A few other developments besides sic period, a branch of directly cause diferent types of cells to 1948 marked a watershed intensive breeding helped make this pos- ancestrally carnivorous grow. The HOX genes are the master guides moment in the creation of the industrial sible. The 1950’s and 60’s were the first theropods emerged as of the development of an embryo along its breeds that make up most of the chickens decades of the heyday of cheap corn, ancient birds towards head-to-tail axis: Change one HOX gene in alive today. It started innocently enough— thanks to intensive farming methods, com- the end of the Jurassic. a fruit fly, and it will develop wings where its with beef being rationed during the war, mercial seed lines, and selective breeding. Recent fossil finds, like antennae should be; change another, and it Americans’ chicken consumption almost Previously, “free-range” chickens weren’t the Sinosauropteryx will grow and extra pair of wings. The HOX doubled, and grocers were interested in a thing because all chickens were free to (discovered in 1996 genes evolved very early in the evolution- keeping sales up. A&P started a contest range—and even if they were fed largely in Liaoning province ary tree—about 500 million years ago, and

38 LUCKY PEACH CHICKEN 39 are found with extremely similar sequences (but not necessarily deletion) of genes that oversight committee will let them hatch it. throughout the animal kingdom (fruit flies, cause tooth buds to develop, among others. But, in a postmodern ending to the story of chickens, and humans alike). Some people (probably most of you) will chickens, as a common, genetically under- But, crucially, the HOX take this as an interesting food for thought stood bird, they are the standard avian genes don’t code for legs or factoid for your next dinner party, or model organism, and thus the natural sub- or wings—the pro- take it as an opportunity to get philosophi- ject of Horner’s reverse evolution. What teins they code for cal with yourself (“All human beauty comes came from dinosaurs through jungle , bind to other from arbitrary diferences in the regulation chicken fancy, and Darwin’s research into sections of DNA, of cells that make structural materials, and the modern chicken is starting to loop the and by binding, the face that gives me my social currency is evolutionary tree into a circle, taking us to turn those genes just an emergent property of transcription dinosaurs once more. off and on. The factors making slight diferences in bone genes that HOX pro- secretion rates in cells in diferent locations! teins bind to don’t code for My idea of myself is an illusion! Society is a leg or a wing either; they in turn a sham!”). A paleontologist named Jack code for proteins that control other genes, Horner is taking it and running with it— the coordination of which eventually leads backwards in time. He looked at evo- to bone or eye (or wing or tail) develop- devo and decided that if we know how ment. HOX genes, and the genes that HOX gene regulation changed tooth into beak proteins bind to, are called transcription formation in the chicken embryo, then, we factors: they control what sections of DNA can just as easily regulate in the other direc- get read and transcribed into RNA, which tion, creating “experimental atavisms”, then gets translated by the ribosome into causing a chicken embryo that natively a protein. An organism can easily have doz- has the code for a beak to develop teeth. ens of transcription factor genes, each of And we can do the same for other regula- which can bind to and regulate a hundred tory pathways—stimulating the embry- or more target genes. And the target genes onic chicken’s pygostyle to develop into might code for a specific enzyme or type of a tail; swooping in and downregulating tissue, but just as often they are also regu- the growth of the long digits that make latory genes, so what gets switched on or up the wing, thus creating a hand instead; of is yet another cascade of switching. and altering the regulation pathway that directs where feathers develop. IF IT SOUNDS COMPLICATED, You’d think that, as the science advi- IT IS! sor for Jurassic Park (he was, really really, the paleontology advisor for both the book But the basic takeaway is that the big and the movie), Horner would know bet- physical diferences in, say, a bird and a ter—Life Finds A Way, after all, and rarely dinosaur don’t actually come from direct are the results clean or predictable—but changes in the genes that directly build he’s forging ahead, working with evo- the tail or wing, but in genetic changes devo labs who study the pertinent reg- that afect the regulation of those genes. ulatory networks in embryos. When and Which means that the changes in dinosaurs if they create an embryo that can actually that led, eventually, to the chicken, were grow (remember the scene in Alien Resur- regulatory: downregulation of tail devel- rection where Ripley finds all the horri- opment, changes in forelimb development bly mutated, earlier attempts to clone that mutated hands into wings, changes in her? That’s basically what an evo-devo the genes that direct the locations where lab’s archive looks like, writ chicken) it follicles develop, and inactivation remains to be seen whether their ethics

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