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|A Gradual Science|
|Plain Monkey Business|
“”INTELLIGENTLY DESIGNS YOU IN HIS PERFECT IMAGE
EAT AND BREATHE THROUGH SAME HOLE
GIVES MEN NIPPLES
ALSO CUT OFF THAT FORESKIN, IT'S GROSS
|—Scumbag God meme|
In many organisms examples of suboptimal design or jury-rigged design can be seen. The existence of suboptimal design is evidence for
intelligent inelegant design. These features can be explained easily by evolution, the "blind watchmaker", which can only act on what it's given to act upon, but not by creationism, or intelligent design (ID) (except by the Theory of "God created it that way to test our faith") which states that a designer God created all organisms with a clean slate. Suboptimal design is generally not discussed in evolution, but there is some examination of the nature of evolutionary constraints. Public defenders of evolutionary theory like to keep it prominent anyway, as an answer to intelligent design's organized complexity and irreducible complexity. It is significant to observe that a single example of a suboptimal or otherwise imperfect design instantaneously falsifies the idea that a master designer has created by its intervention all life specifically tailored to fit its particular niche. The Fall has to be offered as an explanation if ID is to be internally coherent for evidence suggesting an error in the design of life by an allegedly flawless architect.
Thus, suboptimal design forces ID proponents to decide whether they want to be scientists and acknowledge that their argumentation does not work, or pseudoscientists who invent excuses, making their hypothesis unfalsifiable.
Examples of suboptimal design include non-functioning organs, vestigial features in general, and roundabout wiring.
- 1 Non-functioning organs
- 2 Vestigial features
- 2.1 Amniote gill bars
- 2.2 Developmental pathways
- 2.3 Diastataxy
- 2.4 Endosymbiosis
- 2.5 Flowers of asexually-reproducing plants
- 2.6 Plantaris muscle
- 2.7 Pseudocopulation
- 2.8 Seed plants' tiny gametophytes
- 2.9 Unusable wings on ground-dwelling beetles
- 2.10 Vestigial carotids
- 2.11 Human appendix
- 2.12 Male nipples
- 3 Roundabout wiring
- 3.1 Odd biochemical pathways
- 3.2 Cellulose
- 3.3 Descendant testes in humans and other primates
- 3.4 Aquatic air breathing
- 3.5 Endogenous retroviruses
- 3.6 Flounder eyes and mouths
- 3.7 Fused bones
- 3.8 Humeral elevators in Aves
- 3.9 Land-vertebrate blood circulation
- 3.10 Mammalian tidal respiration
- 3.11 Reptile cardiopulmonary capability
- 3.12 Urate oxidase
- 3.13 Vertebrate eye
- 4 A programmer's view
- 5 External links
- 6 See also
- 7 References
Alulas in flightless ratites
The alula is a small structure located at the joint between the hand-wing and arm-wing of birds, and is used for landing. As the adherents of ID argue that a master intelligent designer created all life for its unique purpose, without error, it is most curious that we should see so many superfluous traits in so many taxa. Few examples are better than that of an alula, the "bastard-wing" or mid-wing slot formed by the thumb-borne remex, seen in Rheiformes (Rheidae family, flightless birds from South America), the reason for which is most difficult to account for, under the ID model.
Land-vertebrate side toes
All but some of the earliest tetrapods (land vertebrates and aquatic relatives) have at most 5 digits on each limb; 5 digits is their inferred ancestral state. However, in many cases, some of these digits have become reduced or absent, with the reduced ones having no clear function. In walking limbs, these extra toes no longer reach the ground.
Horse evolution shows an excellent series of intermediates between Hyracotherium, with its four front toes and three rear toes, and Equus, with its single toe on each foot. The intermediates have the central toe enlarged and the toes on each side reduced, until present-day equines have only splints on each side. However, present-day horses are occasionally born with three toes on each foot!
Parallel to horses, most artiodactyls (even-toed ungulates) have had a similar side-toe reduction; the main toes are 3 and 4, with 2 and 5 reduced or absent. Likewise, several carnivores, among them domestic dogs and cats, have shortened toes with claws (dewclaws).
Pandas' thumbs have become non-opposable, but they have evolved a new pseudo-thumb from the bones of the wrist.
Amniote gill bars
The embryos of amniotes (reptiles, birds, mammals) go through a phase where they have gill bars (or Gill slits) and gill pouches, though not functional gills; the aortic arches are to supply blood to these would-be gills.
Characteristics of embryos and the relationship to evolution is a hotly contested issue by the creationists. Haeckel's embryos are a particularly favorite whipping boy, especially in textbook debates.
One of the most striking patterns observed in amniote ontogeny is the presence of highly conserved developmental pathways across lineages, except for a few glaring exceptions. Take for instance digital reduction in the manus. The manus the part of the body to which the distal portion of the forelimb attaches. It is called the hand in primates, the front hoof in terrestrial Ungulates, the front paw in many Carnivores, front flipper in marine mammals. The manus also makes up the wing in birds, bats and pterosaurs. Morse's Law models the stereotypical, symmetrical reduction of manual digits via the loss of digits I and digits V. Certain lepidosaurs (scaled lizards) and theropod dinosaurs mark the only known exceptions to this conserved pattern, in that in these groups digit IV is lost after serving as the organizational axis for the development of the digital arch, while digit I is retained and digit V reduced as usual. This produces a highly specialized asymmetrical postaxial reduction pattern in the manus. Such a seemingly inexplicable anomaly is readily accommodated by evolutionary biology, but it is a significant problem for the ID model. If lizards and dinosaurs were created by the same designer at the same time, why should they display so bizarre a pattern of digital reduction in the manus vis-a-vis all other amniotes?
Diastataxy refers to the peculiar condition observed in basal neornithine lineages (modern birds excluding ratites) in which the fifth secondary remex (flight feather) is missing, but the corresponding secondary covert, is present — leaving a diastema (gap) between the fourth and sixth secondary remiges (plural of remex). How this is the work of a "master designer", or reflective of "intelligent design" is not readily apparent. The ID standpoint becomes most farcical when confronted by the hummingbird Cyanophaia caeruleolavata (Aves: Trochilidae) which is eutaxic in one wing and diastataxic in another! The kingfisher Halcyon pileata (Aves: Alcedinidae) displays an intermediary morphology between the eutaxic and diastataxic condition into adult ontogeny and thus provides a similarly inexplicable "design" quirk. Perhaps more bizarre yet is the hodgepodge distribution of diastataxy throughout Aves. For instance, all Charadrii are diastataxic except Philohela, why? Why was this one particular genus singled out for eutaxy? Within Rallidae (rails) all but eight species are diastataxic. In another two genera of rails, Creciscus and Sarothrura, both eutaxic and diastataxic species exist. Again the question must be, why? Why the erratic distribution of diastataxy and eutaxy? It strains credulity to advance "intelligent design" as the explanation for any of these examples.
Flowers of asexually-reproducing plants
The plantaris muscle is an example of suboptimal design. In the human species it is atrophied (if not absent altogether) and ends in the Achilles tendon without reaching the toes at all. In contrast, in monkeys it is a fully functional muscle that serves to flex all toes at once, and is thus useful for swinging from trees by the feet. Its existence in human beings makes no sense for an intelligent designer, but makes perfect sense if we share a common ancestry with the monkeys; it lost its functionality when we stopped swinging from trees.
Lizards that reproduce by parthenogenesis ("virgin birth"), like the hybrids of certain whiptail-(Cnemidophorus) lizard species, often practice "pseudocopulation", in which a "pseudomale" bites a "pseudofemale" in the neck, inducing egg release. But a parthenogenetic species ought not to need this egg-release stimulus; aphids do not pseudocopulate when reproducing parthenogenetically. So it is clearly a vestigial feature left over from sexually-reproducing ancestors.
The reason why these lizards engage in pseudocopulation is to stimulate their hormonal cycles into peaking, in order to ovulate. Otherwise, they are incapable of automatically ovulating like, say, chickens.
Seed plants' tiny gametophytes
Land plants practice alternation of generations between a diploid sporophyte phase and a haploid gametophyte phase; these phases produce spores and gametes, respectively. The more primitive plants, like mosses, liverworts, and ferns, have prominent sporophyte and gametophyte phases, but seed plants are nearly all sporophyte, having only microscopic gametophytes with only a few cells. The female gametophytes live inside of the parent plant's female reproductive parts (female cone, pistil,…), while the male gametophytes are released inside of pollen grains from the parent plant's male reproductive parts (male cone, stamen,…). When a pollen grain arrives at a compatible female reproductive part, it sprouts a pollen tube that contains the sperm-cell nuclei. This tube grows inside that part toward an embedded female gametophyte, where it fertilizes an egg cell.
This is clearly convergence toward the usual animal state of affairs of being all-diploid except for the gametes; the tiny gametophytes are essentially vestigial, and could easily be done without.
Unusable wings on ground-dwelling beetles
Flight is one of the main characteristics of insects. However, many beetles (order Coleoptera) do not fly, such as some darkling beetles (family Tenebrionidae, e.g. Eleodes species), the Kauai flightless stag beetle (Apterocyclus honoluluensis), and so on. And yet, they have wings. Not only do the beetles live — egg, larva, pupa, and adult — entirely on the ground, and so don't need wings; not only are their wings rather reduced, and so probably couldn't get the critter off the ground even if it wanted to go; no, the real wonder is that the wing covers (elytra) — which are themselves vestigial wings — are fused together, so that the wings cannot be used!
In the Bucorvus genus of birds (the only extant species of family Bucerotidae) and the Phaenicophaeus genus (ex-Rhopodytes genus) of cuckoos, both of the common carotid arteries are vestigial, being present as only fibrous cords. Their vascular function has been assumed by other vessels. The question therefore becomes, why should they be present at all? After all, if Bucorvus and Rhopodytes were designed in six literal days of creation and did not evolve, it follows that the "Master Designer" would have simply designed them with the appropriate vessels carrying out the vascular function of the carotids. Why waste resources on incorporating vestigial carotids into the "design"?
Why do males of almost all mammalian species have nipples? Creationists would be at a complete loss to explain this entirely useless feature. Embryology and evolution do however have an explanation. Mammalian fetuses do not physically differentiate by gender until the male fetus starts producing testosterone. In humans, that is at about 6 weeks. For males, there is little to no disadvantage to having nipples, and hence insignificant evolutionary selection against them. For example, cancer of the nipple is rare and usually occurs after reproduction. Additionally, 1 in 18 people are born with supernumerary nipples.
Odd biochemical pathways
In 2004, Edward J. Behrman, George A. Marzluf, and Ronald Bentley published a paper titled, "Evidence from Biochemical Pathways in Favor of Unfinished Evolution rather than Intelligent Design". The authors began by commenting:
- In teaching metabolic pathways, every instructor emphasizes the chemical logic of the transformations wherever possible. In cases such as those to be described here, the lecturer is reduced to impotent hand-waving.
The examples listed are:
- Unnecessary transformation of a carbon atom from "left-handed" (S) to "right-handed" (R) chirality in the propionyl CoA→succinyl CoA pathway.
- The pathways for several compounds begin by converting (S)-reticuline to (R)-reticuline. It would be simpler to just use S-reticuline.
- Different organisms using different pathways for producing the same compound (the validity of this example might depend on what substrates are available)
- During the biosynthesis of the amino acid tryptophan (link to pathway), a 3-carbon fragment is removed (glyceraldehyde 3-phosphate), and in the next step, a 3-carbon fragment (serine) is added back (actually, in this example, it seems that adding serine is probably a more direct way of getting the "backbone" part of the amino acid — it would take 3 steps to convert the glyceraldehyde 3-phosphate chain (-CHOH-CHOH-CHOPO3) into the amino acid carbon chain (CHH-CHNH3-COO).
- Okazaki fragments. When DNA strands are separated and being replicated, the "leading strand" is continuously copied by a 5'→3' DNA polymerase. The "lagging strand" is unwound 3'→5', but because replication proceeds in the 5'→3' direction on the DNA strand, the lagging strand must be synthesized in short bits that are then pieced together. It is pointed out that it would be simpler and more logical just to use a 3'-5' DNA polymerase on the lagging strand, but this is not what biology does.
- Unnecessary RNA editing. A pre-RNA for an ion channel protein has a particular codon, CAG, that codes for glutamine. However, if the protein that is produced from the RNA contains that glutamine, the mouse dies. In healthy mice, another protein edits the pre-RNA and changes CAG to CIG, which is equivalent to CGG and which produces arginine, the correct amino acid. It would be much simpler for the pre-RNA to just code for CGG to start with, and dispense the editing step. Indeed, scientists have made this change in the lab, and the resulting mice are normal and no longer need the editing step. This appears to be another example of unnecessary irreducible complexity.
Coleridge's fabled ancient mariner might have lamented, were he of biologist leanings, "cellulose, cellulose everywhere and not a polysaccharide to digest." Cellulose is the principal carbohydrate found in plant cell walls, and is highly resistant to tensile forces, owing to its arrangement in long parallel aggregates, much like cables. Composed entirely of glucose monomers, cellulose is rich in chemical energy and presents a tempting meal for any animal that can metabolize it. Inexplicably, there are almost without exception, no animals that can digest cellulose. Those few that do are forced to enlist the aid of bacteria and protozoans in their intestines that synthesize cellulase, an enzyme which can break down the glycosidic bonds that hold cellulose together. The animals that enlist these intestinal symbionts are termites and ruminant mammals (e.g., sheep, goats, cattle, horses, koalas, bison, buffalo, deer, and antelope). Considering the fact that cellulose is among the most abundant organic materials on Earth, one must wonder why the "master designer" incorporated so glaring a defect as inability to digest it, into his multitude of designs.
Descendant testes in humans and other primates
In humans and related primates, males develop testes deep in the abdomen. The testes then descend to the scrotum. In order to accomplish this, a hole must form in the peritoneum (lining of the abdomen) through which the testes pass on their way. This hole is sealed, but not well. This faulty seal is unsuited for bearing the weight of the organs a human puts upon it, and frequently tears in later life, resulting in the most common type of hernia, an inguinal hernia. The challenge for creationism and evolution is to explain this situation.
The evolutionary history of descendant testes
The formation of the testes in the abdomen is a common situation in vertebrates. In cold-blooded vertebrates, it makes sense. The testes work most efficiently if they can be kept at a constant temperature, and the closest thing to constant in a cold-blooded creature is towards the center of the body.
When warm-blooded traits began to evolve, the body temperature of mammals began to exceed the safe functional range of the testes. The testes had to be cooled. Different lines of descent in the mammals have solved this problem in different ways. Some species develop elaborate cooling systems around the testes. Others, such as ourselves and our primate ancestors, move the testes closer to the skin so that they may easily radiate excess heat.
Why form the testes in the abdomen and move them rather than just form them in the scrotum? Because evolutionary change is always easiest to accomplish by tacking steps onto the end of a process rather than modifying existing steps that work. It's just simpler to produce this kind of development. It's easy to see how each step closer to the surface was an incremental improvement in the situation, so this poses no challenge to evolution.
Why isn't the seal on the peritoneum better? Because for most of our evolutionary history, it didn't need to be. Our quadruped ancestors put no great weight on the seal, and so the seal had no tendency to rupture. When we started to walk upright, the weight of our internal organs was no longer borne by the front of our belly and by the supports hanging from our spines, but rather by the lower portion of our peritoneum. The seal that had been more than sufficient since we evolved into mammals suddenly became design flaws.
There has been insufficient evolutionary pressure to produce a more effective arrangement, probably because most inguinal hernias occur late in life; most evolutionary pressure is focused on diseases that occur during reproductive ages and earlier. This is but one of several elements of our anatomy that shows insufficient adjustment from our quadruped ancestors. (Another being the aforementioned organ supports hanging from our spines, which are quite unsuited for life as a biped and are a major cause of lower back pain in later life.)
Creationism and descendant testes
Creationism has a much more difficult time explaining the descendant testes.
In general terms, creationists react to such obvious examples of bad design in various ways, none of which adequately explains the descendant testes.
- Creationists frequently claim that apparent examples of bad design are, actually, good design, if looked at in the proper light. There seems little possibility of finding a "good purpose" for this formative arrangement, and until they come up with one, this is just blowing smoke. By all appearances, this is bad design for which a superior design is readily obvious. Claiming it is anything else requires some support.
- Creationists may lay the blame for bad design on "degeneration" caused by The Fall. It would certainly be possible to posit that the testes were moved from a better location to the abdomen as a result of degeneration, but how to account for them moving back? Isn't this a positive change that would have to occur after their initial misplacement, such that creationists deny is possible? Degeneration of the peritoneum to allow the testes through is probably acceptable to creationists, but the seal, as poorly designed as it is, is still an improvement over no seal, and thus the creationists deny they are possible to form. (That degeneration runs contrary to natural selection, which most creationists claim to accept, is another issue.)
In the end, creationists simply have no effective explanation for the process by which our testes descend. The clearly poorly-executed design of the system, along with an obvious history of improvements to it, denies the foundation of most creationist anti-evolution arguments and the descent of the testes must be seen as evidence against creationism.
Aquatic air breathing
Many animals that live all or most of their life underwater still have to breathe air. These include the cetaceans (whales and dolphins), sirenians (dugongs and manatees), pinnipeds (seals), sea snakes (subfamily Hydrophiinae) and some large turtles. Some extinct groups of fully aquatic reptiles, such as the ichthyosaurs, mosasaurs, placodonts and plesiosaurs, also had to surface to breathe.
These animals do not usually drown, since they do not inhale underwater, but they can suffocate if they don't get to the surface in time. This problem is marked because most aquatic air-breathers are viviparous or ovoviviparous, meaning that they give birth to live young which are born underwater. Taking the first breath is triggered by the touch of air on the skin; post mortems of dead calves sometimes show that they never got to the surface to take that first breath.
Since this is an obvious problem, why not have gills or some other method of exchanging gases (extracting oxygen and removing CO2) with the water? Evolution can explain that these animals evolved from terrestrial animals which had no gills, and these gills haven't been able to re-evolve, but intelligent design offers no solution. It's not like the intelligent designer couldn't include both gills and lungs, especially in newborn animals, if it saw fit, since some animals like lungfish have both and salamanders have functional gills in the early stages of their development. In fact, it is unclear why these animals, especially those like sea snakes and ichthyosaurs with oxygen consumption similar to sharks and other fish, should have to breathe air at all.
For the most part, ERVs are genomic fossils of ancient viruses. Some however, still retain functionality and have to be kept under control by the immune system. Mice lacking immune components undergo reactivation of these sequences.:42
Flounder eyes and mouths
Flounders and other flatfish (halibut, etc.) spend most of their lives lying on the sandy bottom of the ocean. However, unlike skates and rays, flounders clearly have a "jury-rigged" solution to life on the ocean floor. When flounders are young, they swim upright like normal fish. However, as they get bigger, they begin to swim and lay on their sides. The problem with this is that one eye is facing the wrong way, into the sand. The solution? The eye actually pops out of its socket and migrates around to the other side of the face!
Most land vertebrates fuse several of their bones as their grow, typically skulls and pelves, and sometimes other bones, like some limb bones of birds. Why don't they start off in an already-fused state?
Humeral elevators in Aves
Essentially, the avian pectoral apparatus is wired backwards from that seen in the only other extant flying vertebrates, bats. Logically, the dorsal elevators such as the deltoids ought to be the principal muscles affecting elevation of the humerus, and indeed this is what we see in bats. In birds, however, a ventral muscle, Musculus supracoracoideus, affects elevation of the wing via a deflected tendon of insertion. Thus a muscle which initially functioned as a humeral depressor, has undergone a complete reversal in function. Why didn't our alleged "master designer" just wire things right from the outset, with the dorsal musculature elevating the wing? Why the convoluted (literally) system whereby a ventral muscle elevates the wing through a looped tendon of insertion?
Land-vertebrate blood circulation
This starts off in fish-like fashion and gets reorganized, with some aortic arches and other vessels dropping out. Likewise, the heart starts off as a two-chambered, fish-like heart and becomes split into a three-chambered heart and sometimes further into a four-chambered heart with two separate blood paths. But why not start out with some intended final state if that is what is desired? Why build some extra blood vessels, only to throw them away? Why not make the heart start off as three- or four-chambered?
Mammalian tidal respiration
Mammals have a lung ventilation system that is tidal: we breathe in and out through the same tubing. Deoxygenated air is therefore mixed with the fresh, and some of it is re-breathed.
Birds however have a different system. It is 'through-flow': the air follows a circular path round the body to the lungs and out again, so that oxygen-rich incoming air is not mixed with the deoxygenated outgoing air. It has been calculated that the avian system is therefore 10 times more efficient than the mammalian one. That is, mammals — including us humans — have far less efficient lungs than birds.
What makes this doubly odd is that there are many mammals whose lifestyles mean efficient breathing is essential: long-distance runners like wolves and African hunting dogs, and sprinters like cheetahs. And really oddly, the mammalian equivalent of birds, bats. What is it about the bat lifestyle (say, a pipistrelle), compared to the bird lifestyle (say, a nightjar), that means it deserves lungs so inefficient? And conversely, the avian system is found in hawks and albatrosses, pigeons and peregrines. Fair enough. But it's also used in kiwis, penguins and ostriches. What on earth was the designer up to?!
Interestingly, in the case of bats, they have perhaps the most efficient respiratory system of any mammal. It means that bats can make a good go at a bird-like way of life. But it is good in spite of the aforementioned problem. It overcomes the tidal system's disadvantages. But there's the rub: if bats were designed from scratch, why include a disadvantage and use add-ons to fix it? Especially if there is a more efficient system (the bird one) available? If mammals were cars, they all would have one-litre four cylinder engines, regardless of use… and the racing cars — bats — would have had a turbocharger added.
Reptile cardiopulmonary capability
Reptiles display a marvelous example of a cardiorespiratory system which is incongruent with the idea that all taxa were designed without flaw by a master builder. Reptiles are theoretically capable of powering a high resting metabolic rate (equal to or exceeding the avian minimum of 40 kcal/kg0.75/day), but are in fact unable to meet the oxygenation requirements of such a resting metabolic rate. Nevertheless, reptile lungs (especially those of crocodiles) are usually quite large. How can this discrepancy be? Simple: reptile lungs have a low surface area to volume ratio compared to say mammals (i.e. reptile lungs have less branching). They cannot power a high resting metabolic rate because the low blood-flow rate of the reptilian heart is combined with the simple structure of the reptilian lung (size notwithstanding), in which the surface area/volume ratio is itself minimal. Thus, we have yet another example of suboptimal design to contradict the ID model.
An enzyme that oxidizes uric acid into 5-hydroxyisourate, finally yielding allantoin and CO2. Its gene became non-functional in early primate evolution, so overeating animal-derived food can cause gout. This has been hypothesized as a beneficial mutation, since increased plasma urate has protective antioxidant effects that lengthen the lifespan. But still, the protective effect shows up in the blood. Many other enzymes show tissue-specific regulation, so there is no known reason to render this auxiliary gene completely non-functional.
A programmer's view
In 2003 Jim Kent (1960–), at the time a biology graduate student (and later Director of the University of California Santa Cruz Genome Browser Project), gave an interview to Salon on his views of the human genome from a computer science perspective, below is an excerpt:
“”Kent spoke to me in nerdspeak, with geekoid locutions such as the use of "build" as a noun: "That's the most recent build of the genome. Build 31." I was used to hearing biologists talking about the elegance of DNA with what might be called reverence. By contrast Kent spoke of DNA as if it were the most convoluted, ill-documented, haphazardly maintained spaghetti code — not God’s most sublime handiwork, but some hack’s kludge riddled with countless generations of side effects, and "parasites on parasites."
"It’s a massive system to reverse-engineer," he said. "DNA is machine code. Genes are assembler, proteins are higher-level languages like C, cells are like processes… the analogy breaks down at the margins but offers useful insights." It was nearly impossible to tell the working code from cruft, Kent said. "That’s why a lot of people say, 'The genome is junk.'" But that's what he found interesting: a high-quality programmer's code is always self-evident, but legacy assembler handed down from generation to generation of bricoleurs (I'm paraphrasing again) provides a real challenge for people who like puzzles.
- Response to this article on CreationWiki - None of the previous "design flaws" we analyzed is refuted. They merely claim that Creationism does not mean optimal design in the natural world.
- Some More Of God's Greatest Mistakes — Gives many more examples with short summaries
- A 2004 paper: Behrman EJ, Marzluf GA, Bentley R (2004). "Evidence from Biochemical Pathways in Favor of Unfinished Evolution rather than Intelligent Design." Journal of Chemical Education. 81(7):1051-1052.
- Organisms That Look Designed — A subtle (?) reductio ad absurdum for the whole Intelligent Design hypothesis.
- How do whales and dolphins sleep without drowning? by Bruce Hecker, director of husbandry at the South Carolina Aquarium
- See The Blind Watchmaker: Why the Evidence of Evolution Reveals a Universe without Design by Richard Dawkins. ISBN 0393315703.
- Sang-Im Lee et al. The Function of the Alula in Avian Flight. NCBI. 7 May 2015.
- Why do men have nipples? by Andrew M. Simons (September 17, 2003) Scientific American.
- Supernumerary nipples. medlineplus.gov. Retrieved 19 March 2017.
- Evidence from Biochemical Pathways in Favor of Unfinished Evolution rather than Intelligent Design." Behrman EJ, Marzluf GA, Bentley R (2004). Journal of Chemical Education. 81(7):1051-1052.
- Carey, N. "Junk DNA. A Journey Through the Dark Matter of the Genome". Columbia University Press. 20 June 2017.
- Fernbank Science Center's Ornithology Web: Respiration
- The Physiology and Energetics of Bat Flight by Steven P. Thomas & Roderick A. Suthers, Journal of Experimental Biology 1972 57: 317-335.
- Ruben, J. 1995. The evolution of endothermy in mammals and birds. Annual Review of Physiology 57: 69-95.
- Thompson, G. G. & Withers, P. C. 1997. Standard and maximal metabolic rates of goannas. Physiolocial Zoology 30: 611-634.
- Jim Kent home page
- [How I decoded the human genome] by John Sundman (Tuesday, Oct 21, 2003 12:30 PM PDT) Salon