South of Spain: Mar Menor Lagoon
In honor of Darwins' anniversary of On the Origin of Species.
New Papyrus: Darwin
it takes 20 000 genes to make a nematode and 25 000 to make a human
Charles Darwin recognized that the eye would be a real test of the theory of evolution. He suggested that it might be possible to evolve an eye from "imperfect and simple" forms:
"To suppose that the eye, with all its inimitable contrivances for adjusting the focus to different distances, for admitting different amounts of light, and for the correction of spherical and chromatic aberration, could have been formed by natural selection, seems, I freely confess, absurd in the highest possible degree.
"Yet reason tells me, that if numerous gradations from a perfect and complex eye to one very imperfect and simple, each grade being useful to its possessor, can be shown to exist; if further, the eye does vary ever so slightly, and the variations be inherited, which is certainly the case; and if variation or modification in the organ be ever useful to an animal under changing conditions of life, then the difficulty of believing that a perfect and complex eye could be formed by natural selection, though insuperable by our imagination, can hardly be considered real."
Scientists today believe that the eye could evolve from a single light-sensing cell. Scientists disagree over whether it evolved just once, or many times.
It turns out that Nature is both creative and generous with her gifts. Recent research has shown that the tiny marine worm Platynereis dumerilii has two types of light-sensing cells. The eyes of the worm have rhabdomeric photoreceptors, a compound lens formation that is seen almost exclusively in insect eyes. Rhabdomeric photoreceptors are covered in little finger-like protrusions. In its brain, however, it has a different kind of light-sensing cells - ciliary cells that are seen in vertebrate animals. Ciliary cells have hair-like cilia that extend outward and branch out like tiny umbrellas. Two different ways of sensing light in a single organism! images
Researcher Joachim Wittbrodt of the European Molecular Biology Laboratory in Heidelberg, Germany speculates that the ciliary cells may regulate the worm's daily activity cycle, saying "We think they are related to circadian rhythms. We have found that there is a direct connection to the area used for locomotion... In the beginning we had a toolbox... what was in the brain in the worm ends up in our eye." If the animal had two copies of the genes needed to make one kind of photoreceptor, speculates Wittbrodt, then the extra set would have been free to evolve into the other photoreceptor. Different animals would subsequently evolve to use the two options in different ways.
Genome: Ramen noodle folding form (no knots) is fractal globule based on icosa-dodecahedron.
"perfect" genome code
empirical genome code
"perfect" periodic table
I have speculated earlier here and elsewhere, that the human thumb's missing bone and associated muscle evolutionarily moved to become the fused mandible (lower jaw) and tongue.
I posted this comment at a biology website (RDF), in response to why flies have 6 legs and most vertebrates have only 4 [clue - beetles have 4 wings/jaws, reptiles have 4 legs]:
bilateral pentadactyle digits (insect legs/"hands"/wings/"jaws")*
bilateral pentadactyle digits (invertebrate squid tentacles)*
bilateral pentadactyle digits (vertebrate fingers/toes)*
(larval bilateral) pentadactyle digits (starfish or sand dollar)*
icosahedral/pentameric (eg. virus) symmetry (12 oral/anal sets of five cilia)
*digits can be asexually replicated (due to incomplete meiosis?) or mutatively lost, body segments also, so bilateral millipedes simply have axial multiple copies of their earlier rear set, while bilateral vertebrates have axial duplicated the pelvis from the forelimb carriage or axial duplicated the rear limbs on a rear part of the primitive forelimb carriage which eventually moved caudally.
Flies have 6 legs, 2 wings, 2 wing knobs = 10 digits (no jaws just sharp tubes, larval jaws are forelimbs)
Spiders/crabs have 8 legs, 2 pedipalps ("jawclaws") = 10 digits (no wings)
Squid have 8 regular tentacles, 2 long "thumb" tentacles = 10 digits
Reptiles, fish, mammals (primitive) have 10 digits (forelimbs), 10 digits (rear limbs)
Evo-devo, human mandible/tongue associates with the missing thumb bone and muscle, while the maxillae associates with the four fingers (before mandibular separation, all five fingers).
Probably, due to the developmental order, a fly would be more likely born without wing knobs or wings than to be born without legs, since legs seem to be more ancient. One born without a leg pair probably also has other more severe genetic mutations, especially in internal segmental replication. While a reptile with 6 legs must oxygenate them with lungs, sufficient oxygenation is critical (dolphins lost their legs as oxygen conservation became more significant) while small insects' spiracles provide enough O2 for many legs, and wings help gain more O2. Perhaps.
There is an invertebrate (marine proto-crustacean?) which cannot eat unless it locomotes all limbs, its jaws can't chew unless its digits are moving. This would seem very primitive, since lobster claws and fish jaws operate independently from the legs or fins. Note that while larval caterpillars chew using their 4 forelegs/jaws, adult butterflies only suck nectar while still.
Caterpillars chew with forelimbs modified into jaws, during pupation these jaws reform into webbed wings, so butterflies can fly but can't chew. Grasshoppers do not pupate, they go through stages of enlargement and add wings at a certain instar stage (they can't eat at this stage). The adult grasshopper can both leap and fly. Humans have webbing between thumb and forefinger and between maxillae and mandible (cheeks), in flying insects the same genes form webbed wings associated with jaws; initially (ancestrally) this webbing assisted in filter feeding in early marine invertebrate, moving food particles closer to the mouth orifice.
The primitive invertebrate ancestor had an oral-GI-anal pore/tube with 5 mobile cilia, with variable degrees of rigidity (tentacle vs tendon/bone) and inter-digital webbing, depending on whether the food drifted by current (river) or was static and required cilia pulsation and attachment.
Interesting news confirms earlier speculations
Public release date: 20-Apr-2007
[ Print Article | E-mail Article | Close Window ]
Contact: Anna-Lynn Wegener
European Molecular Biology Laboratory
Researchers discover that the centralised nervous system of
vertebrates is much older than expected
The rise of the central nervous system (CNS) in animal evolution has
puzzled scientists for centuries. Vertebrates, insects and worms
evolved from the same ancestor, but their CNSs are different and were
thought to have evolved only after their lineages had split during
evolution. Researchers from the European Molecular Biology Laboratory
(EMBL) in Heidelberg now reveal that the vertebrate nervous system is
probably much older than expected. The study, which is published in
the current issue of Cell, suggests that the last common ancestor of
vertebrates, insects and worms already had a centralised nervous
system resembling that of vertebrates today.
Many animals have evolved complex nervous systems throughout the
course of evolution, but their architectures can differ substantially
between species. ...all these species descend from a common ancestor
called Urbilateria. If this ancestor already possessed a nervous
system, what it might have looked like and how it gave rise to the
diversity of nervous systems seen in animals today is what Detlev
Arendt and his group study at EMBL. To do so, they investigate the
nervous system of a marine annelid worm called Platynereis dumerilii.
"Platynereis can be considered a living fossil," says Arendt, "it
still lives in the same environment as the last common ancestors used
to and has preserved many ancestral features, including a prototype
invertebrate CNS. Comparing the molecular fingerpint of Platynereis
nerve cells with what is known about vertebrates revealed surprising
"Our findings were overwhelming," says Alexandru Denes, who carried
out the research in Arendt's lab. "The molecular anatomy of the
developing CNS turned out to be virtually the same in vertebrates and
Platynereis. Corresponding regions give rise to neuron types with
similar molecular fingerprints and these neurons also go on to form
the same neural structures in annelid worm and vertebrate."...
The findings provide strong evidence for a theory that was first put
forward by zoologist Anton Dohrn in 1875. It states that vertebrate
and annelid CNS are of common descent and vertebrates have turned
themselves upside down throughout the course of evolution.
"This explains perfectly why we find the same centralised CNS on the
backside of vertebrates and the bellyside of Platynereis," Arendt
says. "How the inversion occurred and how other invertebrates have
modified the ancestral CNS throughout evolution are the next exciting
questions for evolutionary biologists."
A similar study involving Platynereis dumerlii comes to much the same conclusion. PZ Meyers has a explanation of this bit of research. This result, that humans are evolutionarily slow has been portrayed as a bit of a surprise, but is something that has been in the works for awhile. For example, as early as 1992 it was known that insulin genes in humans and apes evolved at a slower rate than in monkeys. The phenomena, called the “Hominid-rate-slowdown hypothesis”. was first suggested by Goodman in a 1961 paper entitled “The Role of Immunochemical Differences in the Phyletic Development of Human Behavior” (published in Human Biology) and led to papers being published on the subject up to the present (here and here for example).
updated from earlier post (Vertebrates are inverted invertebrates).
To continue, with slight clarification, if interested:
See Neil Shubins slideshow, especially page 6 slide 5, to compare Hox gene positions in human and fruit fly.
My earlier explanation of primitive pentadactylity (5 digits) didn't well cover the duplication of reptile/mammal rear limbs from the forelimb carriage, this duplication is actually the same as the duplication of (beetle) 4 wings / 4 jaw mouthparts from the primitive frontal digits.
(I've briefed the text)
Dragonflies & damselflies (Odonates) can chew but they can't walk, their 6 legs are for perching and grabbing.
"You can tell a damselfly from a dragonfly thanks to the way they hold their wings - damselflies fold them up over their body when they land (butterfly-like) while dragonflies hold them open (moth-like)..." Interesting, butterflies or moths can walk a bit but can't chew, beetles & grasshoppers can walk and chew but their flight is not so well controlled.
The insect order Neuroptera, or net-winged insects, includes the lacewings, mantidflies, antlions, and their relatives. The adults of this order possess four membranous wings, with the forewings and hindwings about the same size, and with many veins. They have chewing mouthparts, and undergo complete metamorphosis. Neuropterans are soft-bodied insects with relatively few specialised features. They have large lateral compound eyes, and may or may not also have ocelli. Their mouthparts have strong mandibles suitable for chewing, and lack the various adaptations found in most other endopterygote insect groups.
They have four wings, which are usually similar in size and shape, have a generalised pattern of veins. Some Neuropterans have specialised sense organs in their wings, or have bristles or other structures to link their wings together during flight.
The larvae are specialised predators, with elongated mandibles adapted for piercing and sucking. The larval body form varies between different families, depending on the nature of their prey. In general, however, they have three pairs of thoracic legs, each ending in two claws. The abdomen often has adhesive discs on the last two segments. ...ant lions, which bury themselves completely out of sight and ambush prey from "pits" in the soil. Larvae of some Ithonidae are root feeders, and larvae of Sisyridae are aquatic, and feed on freshwater sponges. A few mantispids are parasites of spider egg sacs.
As in other holometabolic orders, there is a pupal stage, generally enclosed in some form of cocoon composed of silk and soil or other debris. The pupa eventually cuts its way out of the cocoon with its mandibles, and may even move about for a short while before undergoing the moult to the adult form. Adults of many groups are also predatory, but some do not feed, or consume only nectar. They are delicate or cumbersome flyers, the spoon wings have rear wings like birds of paradise. Nemoptera
It's a springtail (Collembola) - a member of a group of arthropods closely related to (but distinct from insects). They get their common name from a long forked organ, the furcula, that usually sits folded up under the abdomen. The earliest fossil hexapod, and one of the first terrestrial animals, Rhyniella praecursor, is a springtail...'Gomph's live in Antarctic mainland, springtails importantly make soil. Tail derived from crab/crayfish folded tail?
Orobophana pacifica: They are tiny, live on coral rubble on Cook Islands. Even though they live on land they aren't closely related to the "true" landsnails in the order Stylommatophora. To see the difference you need to look into their eyes. If you click on the image above to get a high resolution version you might just be able to see the eye - it's a black dot just underneath the tentacles ("feelers"). In true landsnails like the ones you find in you garden the eyes sit on the ommatophores, a second set of tentacles which are retractable.
bird feet, talons, webbing
Can you walk and talk and chew gum at the same time ?
The mechanics of being Human: a self-balancing, 28-jointed adaptor-based biped; an electro-chemical reduction plant, integral with segregated stowages of special energy extracts in storage batteries, for subsequent actuation of thousands of hydraulic and pneumatic pumps, with motors attached; 62,000 miles of capillaries.... R. Buckminster Fuller-
Bucky: Dictators never create their own opportunities.
A neat series of articles on human facial expressions (non-verbal communication), especially interesting after having read that human cheeks are merely muscular/fatty webbing connecting the mandible to maxilla like butterfly wings. Makes me wonder about the link of the smile to the crinkling of the eyelids or the tightening of the eyebrows, all these facial muscles which communicate internal feelings instantly which are usually masked by reflexive social gestures. They must have evolved in deep time, and gradually fine tuned in humans, a super-social species.
Human social traits: anonymous, cooperative, infants
Hrdy sociality hypothesis
Corneal blink reflex: trigeminal nerve senses, facial nerve motors to blink at bright light or loud sound or irritating particle in eye.
Pupillary light reflex
Pigmentation in desert lizards
Pigmentation in humans: Baltic blonde & blue eyes from Gulf stream & grain?
"There is only one spot on the planet where grains will grow despite sub-arctic sunlight.
It is where the warm waters of the Gulf Stream wash ashore. The Baltic is the only place on earth where ocean currents keep it warm enough to grow grain despite dim sunlight. When the inhabitants of this region switched to grain about 6 KYA, they suddenly got insufficient vitamin D to survive. They had stopped eating mostly meat and fish in a place where sunlight was too dim to produce vitamin D in normally pigmented skin. And so they adapted by retaining into adulthood the infantile trait of extreme paleness. Blonde hair and blue eyes were other infantile traits that were just swept along accidentally."
Why did they shift from hunting/gathering (grain processing sorghum in Mozambique 100ka) to complete absolute dependence on grain? What about their cattle/goats/dogs? Fishing seems to have increased rather than decreased amongst Baltic sea peoples with better boat/net technology. Camouflage is always important, whether for predator, prey or combat, but less for farmers. Clothing in cold? Baltic was warm in winter? Europeans also adapted by retaining the ability to digest lactose in adulthood, obtaining vitamin D from milk.
Medieval rural Briton women had wider thicker bones than city women
Whale fossil 4.5ma in Spain: deposited on seafloor 50m deep, now 80m above ground 24km inland. So 4.5ma Medit was high, or tectonic uplifting or both.
Dwarf suction-feeding Australian baleen whale