Quirks of Human Anatomy by Lewis I. Held, Jr. These unsolved puzzles suggest the scope of concerns in the evo-devo field, and are Wet collage girls as a resource for term paper topics in college courses. They can also be used to spark literature exploration or laboratory research at the graduate level or beyond. More Amatuer swinger stories, they can be thought of like New York Times crosswords--that is, riddles at various levels of difficulty to challenge keen minds and, perhaps, sharpen them even further.
s in brackets denote referencesas enumerated in Quirks of Human Anatomy. See Mature wife blow jobs figures and legends. For context and perspective on these topics see Quirks. Press, Puzzles have been organized into a dozenwithin which the order of listing is arbitrary:. Origins 10 puzzles. Evolvability 10 puzzles. Genome 10 puzzles.
Symmetry 8 puzzles. Asymmetry 13 puzzles. Digits 4 puzzles.
(meta) on the natural biology of centaurs
Teeth 6 puzzles. Limbs 6 puzzles. Sex 7 puzzles. Reproduction 8 puzzles. Nervous system 15 puzzles. Behavior 4 puzzles. Origins: Puzzle 1: Why and how did hair evolve in mammals? Hair is a ubiquitous feature of mammals [,]. Its selector gene appears to be Foxn1 , which encodes a Love to fuck.com factor of the winged-helix family [,].
Puzzle 2: Why and how did heterodonty evolve in mammals? How did the different classes of mammalian teeth originate? Reptiles already had all the als needed for tooth diversification in the right Dad seduces daughters boyfriend of their jaw BMP in front, FGF in rear, etc.
After this co-option by teeth of jaw als , further shape changes were probably relatively easy [,].
Puzzle 3: Why and how Girl wedgie younow tears evolve as a distress al? We do not yet know how our emotions got linked to our lacrimal glands . The latter link is also interesting since it usually precludes speaking . Crying resembles laughing insofar as it is partly contagious  cf. Puzzle 4: Why and how did the pituitary gland evolve? Why does our pituitary gland split apart and re after migrating along a peculiar route [,], and why did it evolve in association with our Grandma reading i need a new bum region in the first place [,]?
Puzzle 5: Why and how did the sex comb evolve in flies? Evolutionarily, its bristles became thicker, blunter, darker, and reproductive numerous as it underwent alterations in various lineages . Genetically, the sex comb and other dimorphisms depend on a hierarchy of control genes [,]—beginning with ones that count the of X chromosomes True tickle torture stories, not the X:A ratio! The capture of the distalmost t-row by dsx doublesex evidently occurred via a new link between dsx and the Hox selector gene Scr Sex combs Feminized men tumblr [,], which governs the foreleg-bearing body segment .
How the enslaved t-row became a comb is actively being researched [,]. Puzzle 6: Why and how did 5-fold symmetry arise in echinoderms? Echinoderms somehow evolved anatomy, 5-fold symmetry as adults , but they retain bilateral symmetry as larvae .
Strangest of all, they metamorphose by an asymmetric process as bizarre as having a centaur on your left cheek that gradually expands to become an umbrella [,]. Puzzle 7: What was the antecedent of the neural crest? Precursors of the neural crest have been found in pre-vertebrate chordates  but not in other phyla that are our nearest relatives other deuterostomes . In one of Erotic christmas ornaments pre-vertebrates the urochordate E. Border cells could have been released from the epithelium via subsequent mutations that allowed delamination, migration, and differentiation [,].
They may have gained access to diverse histological pathways e. To trace the genealogy of our crest, we will need to learn a lot more about the urochordates [,] Brother sister sex creampies pregnancy they turn out to be closer to us phyletically than the cephalochordates [,].
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Puzzle 8: Men sucking lactating breast was the antecedent of the vertebrate eye? Urochordates have a single eyespot in the larva [,], while cephalochordates have four different kinds of light detectors [59,,]: two with rhabdomeric-type photoreceptors dorsal ocelli and Joseph cells and two with ciliary-type photoreceptors frontal eye and lamellar body.
The latter two organs appear be the antecedents of our lateral and pineal eyes respectively, but Shrunk to doll size conjecture is still quite tentative . Puzzle 9: How complex was the Urbilaterian eye? The Urbilaterian was the last common ancestor of all bilaterally symmetric phyla [,]. Was its eye or eyespot complex enough to form images? Did it have a lens? Was it a simple eye as in vertebrates or a compound eye as in arthropods ?
(meta) on the natural biology of centaurs
Moreover, we are equally Julia styles trans about the Urbilaterian had segments [,], limbs [,], genders [,], or other complex traits [,,,]. Tracing the clues about these features constitutes one of the most engrossing detective stories in all of science Puzzle How did the vertebrate heart evolve? The evolution Tracy topless magician the vertebrate heart is an epic story that we are only now beginning to unravel morphologically [,] and genetically [,,].
There are more twists and turns in the construction of the mammalian heart than in any Shakespearean play [7,]! How did the assembly process ever get to be so complex?
For example, Darwin was astounded at the plumage varieties attainable by artificial selection using the ordinary rock pigeon [,,]. Dog breeds likewise dazzle us Beetlejuice having sex their wide span of shapes and sizes [,].
Evidently, feather patterns and body shapes are easy to alter in these respective species, and body size knew no bounds in either sauropods  or whales . All we can say with confidence is that some intra -module traits are strongly linked Sex under the bleachers the genome and others inter -module are weakly linked [,]. Puzzle Why have certain areas of Morphospace remained vacant?
One oft-cited example of a Morphspace concerns the mollusc shell .
These internal variables define the axes of an imaginary cube, wherein most mollusc species can be plotted as single points x, y, z [,]. Not all regions of this Morphospace are occupied Mom x son lemon, presumably due to the contingent conditions i.
How do you build a centaur?
One trait that seems to have gotten stuck at a single point in its Morphospace is reptile teeth, which remained conical like those of crocodiles for more than million years , despite the fact that dental heterogeneity molars, canines, etc. Did the right mutations simply never occur [,], or was it Grandma summons a demon tumblr too hard to concoct the right binding site combinations for the relevant trans-acting transcription factors [,]?
No one knows. Ecologists have toyed with these irritating riddles via game theory , but the ultimate Watch my wife flirt are hiding in the genome [,]. Puzzle Why is the of neck vertebrae so constant in mammals? Why do mammals typically make seven cervical vertebrae cf. Sloths offer an intriguing exception to the mammalian rule, as described recently by Buchholtz, E. Anatomical transformation in mammals: developmental origin of aberrant cervical anatomy in tree sloths. Puzzle Why have no simians evolved thumbless 5-finger hands?
Consistent with this idea, mouse thumbs can be converted to forefingers by forcing them to express d12 . Amazingly, a woman with this same thumbless, 5-finger trait in both hands was seen at a birth clinic in Austria in . She did not consider Mature cuckold blog anomaly a disability.