lpetrich

Another one: vampirism. Drinking animals' blood and plants' sap. That has independently evolved many times:

Blood:
Insects: fleas, lice, mosquitoes, etc.
Arachnids: ticks, mites
Annelids: leeches
Vertebrates: vampire bat, vampire finch

Sap:
Insects: aphids, etc.

-

Societies with many non-reproducers (eusociality):

Several hymenopterans: ants, various bees, various wasps
Termites
Naked mole rats
etc.

Flightless workers: ants and termites
Which is why termites are sometimes called "white ants", though they are non-hymenopteran. Unlike "true" ants, which are descended from wasps, termites are descended from cockroaches.

cajela

Thanks to all on the marsupial thing. Idle curiosity can take you to some very interesting places.

lpetrich

Which of the two aortic arches is kept:

Birds - right
Mammals - left

How can one tell whether or not some structure had evolved separately?

A simple test is whether they had originated from different, non-homologous structures. Human hands and elephant trunks are an obvious example; hands are modified front feet, while trunks are modified noses.

That's also the case for the numerous venom injectors mentioned earlier. Snake fangs are modified teeth, while bee and wasp stingers are modified ovipositors (egg-laying tools).

Sometimes multiply-evolved structures have homologous origins; flying vertebrates' wings are all front limbs. However, birds' wings have numerous anatomical similarities not shared by bats' wings or pterosaurs' wings, and likewise for the other two groups. Such differences will suggest multiple origins.

And if the organisms' closest relatives lack a feature, then by parsimony that also suggests multiple origins of that feature. This can have problems if a feature is very easy to lose, as with flightless birds. But it is nevertheless useful, especially for features that are seldom lost or only lost under relatively unusual conditions. By unusual is meant something like like cave animals and underground animals becoming blind. Interestingly, such blind animals often have vestigial eyes or eye parts.

Camera eyes are a good example. By the structural-difference criterion, vertebrate and squid/octopus lens-camera eyes very likely had separate origins. This agrees with the closest-relatives-absence criterion; invertebrate chordates and other invertebrate deuterostomes lack lens-camera eyes, as do other mollusks and most other protostomes.

Berthold

But, what about byssus?

davidannis

You'd only expect that if the designer were not omniscient and omnipotent. An omniscient designer would see all of the possibilities and am omnipotent designer would have no more trouble implementing 1,000,000 designs than one. I think this is sort of like telling my kids to pick up their socks.

--
David
http://www.teachthecontroversy.com

lpetrich

I wouldn't bet on insects and arachnids having a shared silk-making ancestor; there are very many insects and arachnids that do not make silk, and none of their closest relatives do (crustaceans for insects, and horseshoe crabs for arachnids).

Referring to the Tree of Life's arthropod phylogeny, and making blue for groups where some members make silk and green for groups where most members make silk.

Arthropoda:
<Pancrustacea> (insects, crustaceans)
<Chelicerata> (arachnids, horseshoe crabs <Xiphosura>, etc.)
<Myriapoda> (centipedes, millipedes)
<Trilobita> (trilobites)
Various Cambrian arthropods, like Opabinia and Anomalocaris

Pancrustacea:
Insects
Crustaceans

Insects:
(various primitive insects)
Winged insects <Pterygota>

Winged insects:
Straight-winged insects (dragonflies, etc.)
Folded-winged insects <Neoptera>

Folded-winged insects:
<Orthoptera> (grasshoppers, crickets)
<Dictyoptera> (cockroaches, termites)
<Embiidina> (webspinners)
<Hemiptera> (true bugs)
<Holometabola> (four-stage insects)
Etc.

Four-stage insects:
<Coleoptera> (beetles)
<Diptera> (flies, mosquitoes)
<Siphonaptera> (fleas)
<Lepidoptera> (moths, butterflies)
<Hymenoptera> (wasps, bees, ants)
Etc.

Lepidoterans' closest relatives are related by: ((Diptera, Siphonaptera), Lepidoptera). Hymenopterans' silk production is not nearly as well-known as lepidopteran or spider silk production.

Chelicerata:
<Xiphosura> (horseshoe crabs)
[color="blue]Arachnida[/color]

Arachnids:
<Araneae> (spiders)
Scorpions
<Acari> (ticks and mites)
etc.

So silk has likely been invented at least four times among arthropods; spiders, ancestral moths (Lepidoptera), ancestral wasps (Hymenoptera), and webspinner insects. But if silk had been invented by some ancestral arthropod, then it must have been lost many more times.

Codec

This prompts the fact that dynamic adaption to the environment is quite popular.

Chameleon, squid and octopi, I believe some spiders can change their colour too.

Berthold

Flatfish do it, too. The best known spider with this ability is this one. Many animals, though, change colour for various other reasons than camouflage; among them even the proverbial chameleon.

Nice Squirrel

This homoniod can too...

http://anomalies-unlimited.com/Jackson.html

Sorry, just too tempting.