Answering any questions on Evolution

[USincognito]

Why would it be advantageous to have lighter skin at high latitudes?

The most simple reason would be vitamin D production. When you live in climates where you get less sun, have more overcast days and times of the year where they days are very short, your body can cease or have lowered natural vitamin D production leading to rickets.

 

[plindboe]

Why would it be advantageous to have lighter skin at high latitudes?

Darker skin is better able to protect against the harmful effects of sunlight, but with lighter skin more D vitamin can be generated with less sun exposure. Since there's less sun exposure at higher latitudes, due to the angle of the sun and increased use of clothing, the skin will have to be lighter to generate enough D vitamin.

The exception is in populations where vitmain D isn't limited in the diet, for instance eskimos, whose diet consist mainly of fish and other D vitamin rich sources, tend to have darker skin.

Peter

 

[bobsterInJapan]

The most simple reason would be vitamin D production. When you live in climates where you get less sun, have more overcast days and times of the year where they days are very short, your body can cease or have lowered natural vitamin D production leading to rickets.

Darker skin is better able to protect against the harmful effects of sunlight, but with lighter skin more D vitamin can be generated with less sun exposure. Since there's less sun exposure at higher latitudes, due to the angle of the sun and increased use of clothing, the skin will have to be lighter to generate enough D vitamin.

The exception is in populations where vitmain D isn't limited in the diet, for instance eskimos, whose diet consist mainly of fish and other D vitamin rich sources, tend to have darker skin.

Peter

Cool!

 

[Wiccan_Child]

The gist here is correct, although the details are a bit more complicated. There are multiple genes that control the production of melanin, and many have them have had mutations under positive selection in human populations outside Africa. For example, a mutation in the gene SLC24A5 is present in all Europeans but not at all in sub-Saharan Africans. The European version clearly started as a single, fairly recent mutation, which spread rapidly because it was advantageous to have lighter skin at high latitudes. In Africa, however, the gene shows every sign of not having recently come from a single copy, but instead of being been around in a large population for a very long time. (Basically, the European version resides on a single DNA background that looks identical in everyone in the population, while the African versions reside on many different backgrounds, showing a long history of mutation and recombination.)

Interesting

 

[Wiccan_Child]

Why can bacteria maintain a viable long-term population from two 'individuals', whereas, e.g., two dogs cannot?

They reproduce asexually, so no inbreeding. Two sexually reproducing organisms will quickly develop severe inbreeding. This is what happens in humans:

(King Charles II of Spain)

There are bacteria that reproduce in other, crazy ways, and there's lateral gene transfer, etc, but the main idea is that in large, complex organisms like humans, generations of inbreeding causes the small, rare defects to accumulate, polluting the gene pool. This is what we see in Mormon and Amish communities, where rare genetic brain disorders are unusually common due to polygamy and inbreeding.

 

[Naraoia]

Thanks everyone for your interesting replies. I feel as though I have learnt something.

I have a very different question this time. It is related to DNA but a somewhat different concept to natural selection, as far as I can understand it. Namely, taking the example of the dogs in that chart above. I think it would be fair to say that all dogs have one common first ancestor of dog. Suppose the first ancestor of dog was created with all the DNA of the dogs included in that chart. However the first generation puppies, though having approx. the same amount of variety of DNA, would have no choice but to mate amongst themselves, which in itself would pose no problems with birth defects because they still have a large variety of DNA. However, after a number of generations, these dogs divided up into different families, and each family moved further and further apart from each other. After more and more generations, these families became different 'breeds' of dogs. However, now, none of these breeds have anywhere near the amount of variety of DNA that the first ancestral dog had.

For a single dog to have all the genetic variety of all dog breeds, it would probably need extra copies of many genes. I don't know any details about dog genetics, but considering the number of different breeds we've been able to coax out of them, there must be a lot of variation involved. A pair of ancestral dogs could have at most four varieties of each gene between them. (Dogs are diploid.) For every gene that exists in more than four versions in the full gene pool of living dogs, you need either extra copies in the ancestors that were then lost, or new variation that arose since the common ancestors. Whether lots of extra genes are a biological problem or not is hard to guess without knowing the details, but it doesn't sound likely.

Now for my question, if someone were to study the DNA of these various modern dog breeds, would their DNA give the illusion of being evolved via natural selection? Richard Dawkins sometimes mentions the phrase "illusion of design", could an illusion of evolution be possible?

Technically, losing genetic variation WOULD be evolution. We may even be able to reconstruct what really happened, since the gene losses would run in families. So... it wouldn't be an illusion of evolution, but bona fide evolution.

Whether the remaining variation would look selected... I've got to chew on that some.

Each puppy would have a distinct genetic code.

<pet peeve> Not unless dogs can give birth to bacteria or something... Genetic code - Wikipedia, the free encyclopedia </pet peeve>

 

[bobsterInJapan]

Hi again, I'm back in this thread with more silly questions.

It appears that bacteria hasn't really evolved much at all, all these millions and millions of years. Their 'branch' in the evolutionary hierarchy appears to be very short, twig-like, perhaps.

Well, if bacteria has not been left here intentionally, what, would you image, would the world be like without bacteria in the case where bacteria evolved into little bunny rabbits instead, for example?

 

[plindboe]

It appears that bacteria hasn't really evolved much at all, all these millions and millions of years. Their 'branch' in the evolutionary hierarchy appears to be very short, twig-like, perhaps.

They have been evolving all these years as well, and they are hugely successful; human success is not even comparable. Fun fact: There are 10 times more bacterial cells in and on the human body than there are human cells. We're basically their vehicles.

Well, if bacteria has not been left here intentionally

Why assume intent?

what, would you image, would the world be like without bacteria in the case where bacteria evolved into little bunny rabbits instead, for example?

Bunny wabbits couldn't evolve without bacteria, because the existence of bacteria is a necessary condition for the existence of bunny wabbits. For instance bacteria fix nitrogen, and nitrogen is part of amino acids, the building blocks of proteins. Also, wabbits require bacteria in their digestive tract in order to digest food properly.

Peter

 

[Wiccan_Child]

Hi again, I'm back in this thread with more silly questions.

No question is silly!

It appears that bacteria hasn't really evolved much at all, all these millions and millions of years. Their 'branch' in the evolutionary hierarchy appears to be very short, twig-like, perhaps.

Actually, they're one of the most diverse (about 10[sup]7[/sup] species) and populous (total biomass exceeds that of plants and animals) groups on Earth.

Don't mistake unicellularity for evolutionary stagnation. While you can get 'living fossils' which haven't changed much over millions of years, bacteria are quite dynamic.

Did you know that there's a species of bacteria that can use nylon production in its diet? Nylon wasn't invented till the 1930s.

Well, if bacteria has not been left here intentionally, what, would you image, would the world be like without bacteria in the case where bacteria evolved into little bunny rabbits instead, for example?

It's a good question. For whatever reason, bacteria didn't evolve into large, complex, multicellular life - they do form slime colonies that are eerily clever, though.

Myxobacteria have one of the, if not the, most complex life cycle among bacteria, and form almost macroscopic fruiting bodies.

Simple, fungus-like structures. Maybe fungi or bacteria could have taken the place of animals, that's what we'd look like?

 

[plindboe]

No question is silly!

Why is the Moon made of Jell-O?

Peter

 

[bobsterInJapan]

For whatever reason, bacteria didn't evolve into large, complex, multicellular life -

You mean the bacteria that exists today, right?

Weren't all the animals and us suppose to have evolved from bacteria?

 

[USincognito]

You mean the bacteria that exists today, right?

Weren't all the animals and us suppose to have evolved from bacteria?

No, for two reasons. The split between (archaically called) prokaryotes and eukaryotes led the eukaroyote line to fungi, plants and animals. And the split occured well before that point. It's still a pretty complicated scenario, so check out this webpage. The site it's located on is pretty awesome in showing how evolution works.
Life on Earth

 

[Wiccan_Child]

You mean the bacteria that exists today, right?

Weren't all the animals and us suppose to have evolved from bacteria?

Ah, no. Life is split into three large kingdoms (unless you adopt the 2004 6-kingdom system):

• Bacteria - true bacteria.
• Archaea - single-celled organisms superficially similar to bacteria, but with various internal goings on more similar to eukaryotes.
• Eukarya - plants, animals, fungi, etc.

Those three kingdoms are themselves descended from the universal single common ancestor. The descendants of that ancestor split went three different ways. One twig of one branch of Eukarya became multi-cellular. We are on that twig.


Does that make sense?

 

[Naraoia]

Hi again, I'm back in this thread with more silly questions.

No, your questions are fun!

It appears that bacteria hasn't really evolved much at all, all these millions and millions of years. Their 'branch' in the evolutionary hierarchy appears to be very short, twig-like, perhaps.

Bacteria are kind of weird when it comes to evolving. Some of them have looked and lived the same way for literally hundreds of millions of years. Things like the bacteria discussed here are the closest things we have to a true living fossil. On the other hand, they come up with nylonase, evolve to feed on other things they couldn't eat before, become resistant to antibiotics etc. in mere decades. So clearly a lot of evolution goes on in those simple little cells - it just doesn't tend to be as obvious as a new kind of limb

Bunny wabbits couldn't evolve without bacteria, because the existence of bacteria is a necessary condition for the existence of bunny wabbits. For instance bacteria fix nitrogen, and nitrogen is part of amino acids, the building blocks of proteins. Also, wabbits require bacteria in their digestive tract in order to digest food properly.

Not to mention that bunny wabbits power their bodies with oxygen, and guess who makes that? (In fact, guess who uses that oxygen to power the bunny?)

Oh gods. Bacteria really do rule us all.

You mean the bacteria that exists today, right?

Weren't all the animals and us suppose to have evolved from bacteria?

Haha, you managed to stumble on one of the toughest questions in evolutionary biology. Life is nowadays divided into three great domains: bacteria, archaea and eukaryotes. Bacteria and archaea are prokaryotes: they have relatively small and simple cells with no nucleus and little in the way of organelles. Eukaryotes, which include animals, are made of bigger cells that are much more complex inside. The problem is no one is really sure how the three domains are related, and where eukaryotes come from.

For example, eukaryotes and archaea use very similar proteins to copy, repair and otherwise manipulate DNA; however, the cell membranes of eukaryotes are more like those of bacteria. It's been proposed that eukaryotes are basically a happy union of a bacterium and an archaeon, but the debate is far from settled as far as I'm aware. Because (1) these three lineages split so long ago and (2) prokaryotes can swap genes with just about anything, it's very difficult to disentangle their history.

I think the question isn't really whether we came from bacteria - but rather how much of us came from them, and exactly how.

However, there is a way in which every eukaryote, animals included, did come from bacteria: one of the most important organelles in your cells descends from them. Mitochondria, which produce most of the cell's energy, are thought to be most closely related to alpha-proteobacteria, and they actually have several living relatives that live as parasites or symbionts (or a bit of both) inside the cells of various animals.

... got a bit carried away there, didn't I?

 

[SkyWriting]

Bacteria are kind of weird when it comes to evolving. Some of them have looked and lived the same way for literally hundreds of millions of years.

That's because the environment of the world has been static and unchanging for 100's of millions of years.
Also, those particular bacteria have not experienced any changes in their nutrient sources for hundreds of millions of years.

Or they would have evolved, of course. Here are others:

Mammals


Echidnas are one of few mammals to lay eggs.
Aardvark (Orycteropus afer)
Amami rabbit (Pentalagus furnessi)
Chevrotain (Tragulidae)
Cypriot mouse (Mus cypriacus)
Elephant shrew (Macroscelidea)
Laotian Rock Rat (Laonastes aenigmamus)
Iriomote cat (Prionailurus iriomotensis)
Monito del Monte (Dromiciops gliroides)
monotremes (the platypus and echidna)
Okapi (Okapia johnstoni)[5]
Sumatran Rhinoceros (Dicerorhinus sumatrensis)
Birds


Hoatzin are born with two visible claws on their wings, but they fall out once they reach maturity.
Acanthisittidae (New Zealand "wrens") &#8211; 2 living species, a few more recently extinct. Distinct lineage of Passeriformes.
Broad-billed Sapayoa (Sapayoa aenigma) &#8211; One living species. Distinct lineage of Tyranni.
Bearded Reedling (Panurus biarmicus) &#8211; One living species. Distinct lineage of Passerida or Sylvioidea.
Coliiformes (mousebirds) &#8211; 6 living species in 2 genera. Distinct lineage of Neoaves.
Hoatzin (Ophisthocomus hoazin) &#8211; One living species. Distinct lineage of Neoaves.
Magpie Goose (Anseranas semipalmata) &#8211; One living species. Distinct lineage of Anseriformes.
Seriema (Cariamidae) &#8211; 2 living species. Distinct lineage Cariamae.
Andean Condor (Vultur gryphus) and California Condor (Gymnogyps californianus) is a two living members of the New World Vultures.
Osprey (Pandion haliaetus) and Northern Crested Caracara (Caracara plancus) are two living members of the Raptor family.
Reptiles


Crocodilians survived the K-T extinction that killed off the dinosaurs.
Alligator Snapping Turtle (Macrochelys temminckii)
Crocodilia (crocodiles, gavials and alligators)
Pig-nosed turtle (Carettochelys insculpta)
Snapping Turtle (Chelydra serpentina)
Tuatara (Sphenodon punctatus and Sphenodon guntheri)
Amphibians
Giant salamanders (Cryptobranchus, and Andrias)
Purple frog (Nasikabatrachus sahyadrensis)
Jawless fish
Hagfish (Myxinidae) Family
Northern Brook Lamprey (Ichthyomyzon fossor)
Bony fish


Tuataras are reptiles, yet more primitive than either lizards or snakes.
Arowana and Arapaima (Osteoglossidae)
Bowfin (Amia calva)
Coelacanth (the lobed-finned Latimeria menadoensis and Latimeria chalumnae)
Gar (Lepisosteidae)
Queensland lungfish (Neoceratodus fosteri)
Sturgeons and Paddlefish (Acipenseriformes)
Bichir (Polypteridae) Family
Protanguilla palau
Sharks
Blind shark (Brachaelurus waddi)
Bullhead shark (Heterodontus sp.)
Elephant shark (Callorhinchus milii)
Frilled shark (Chlamydoselachus sp.)
Goblin Shark (Mitsukurina owstoni)
Gulper Shark (Centrophorus sp.)
Invertebrates
Insects


The coelacanth was thought to have gone extinct 65 million years ago, until an intact specimen was discovered in 1938.
Mantophasmatodea (gladiators; a few living species)
Mymarommatid wasps (10 living species in genus Palaeomymar)
Nevrorthidae (3 species-poor genera)
Notiothauma reedi (a scorpionfly relative)
Orussidae (parasitic wood wasps; about 70 living species in 16 genera)
Peloridiidae (peloridiid bugs; fewer than 30 living species in 13 genera)
Sikhotealinia zhiltzovae (a jurodid beetle)
Syntexis libocedrii (Anaxyelidae cedar wood wasp)
Crustaceans


Nautilus still retain the external, spiral shell that its other relatives have lost.
Glypheoidea (2 living species: Neoglyphea inopinata and Laurentaeglyphea neocaledonica)
Stomatopods (mantis shrimp)
Triops cancriformis (also known as tadpole shrimp; a notostracan crustacean)
Molluscs
Nautilina (e.g. Nautilus pompilius)
Neopilina galateae, a monoplacophoran
Ennucula superba &#8211; nut clam
Vampyroteuthis infernalis &#8211; Vampire Squid
Other invertebrates
crinoids


With little change over the last 450 million years, the horseshoe crab shows a strong resemblance to the extinct trilobites that roamed ancient earth, thus making the horseshoe crab appear as a living fossil.
Horseshoe crabs (only 4 living species of the class Xiphosura, family Limulidae: Limulus polyphemus,Tachypleus gigas, Tachypleus tridentatus and Carcinoscorpius rotundicauda)
Lingula anatina (an inarticulate brachiopod)
Liphistiidae (trapdoor spiders)
Onychophorans
Valdiviathyris quenstedti (a craniforman brachiopod)
Paleodictyon nodosum (unknown)

 

[MrMoe]

why did archeopteryx evolve feathers?

 

[plindboe]

why did archeopteryx evolve feathers?

Archeopteryx didn't evolve feathers, it inherited them. Likely feathers initially evolved for thermal insulation, but has since been co-opted for display, gliding and flight.

Peter

 

[MrMoe]

Archeopteryx didn't evolve feathers, it inherited them. Likely feathers initially evolved for thermal insulation, but has since been co-opted for display, gliding and flight.

Peter

so who did it inherit them from and how were they co-opted into something they were not original intended for?

 

[Wiccan_Child]

so who did it inherit them from and how were they co-opted into something they were not original intended for?

Whichever species evolved them first. Archaeopteryx couldn't fly - it only used them for their original purpose, which was thermal insulation. Later, one of its arboreal (tree-dwelling) cousins found that these feathers, as well as providing thermal insulation, also aided jumping - you can jump further with feathers.

There was the first species who evolved feathers for thermal insulation. It split into numerous other species. One was Archaeopteryx. Another was a tree-dwelling species that jumped from tree to tree. Its feathers provided a distinct advantage, to the point that natural selection could coop the feathers and make them more about gliding and less about thermal insulation - the trade-off was worth it.

From there, gliding can become better and better with lighter bones, bigger and more aerodynamic feathers, etc. And from there, you get true flight.

Note: I glossed over the exact origin of the feather. Over the generations, speciation occurred, and new species evolved different scale structures, some of which approached what we now know to be feathers. Just when these filament structures constitute true feathers is somewhat subjective. Wikipedia, as ever, has more.

 

[MrMoe]

Whichever species evolved them first. Archaeopteryx couldn't fly - it only used them for their original purpose, which was thermal insulation. Later, one of its arboreal (tree-dwelling) cousins found that these feathers, as well as providing thermal insulation, also aided jumping - you can jump further with feathers.

There was the first species who evolved feathers for thermal insulation. It split into numerous other species. One was Archaeopteryx. Another was a tree-dwelling species that jumped from tree to tree. Its feathers provided a distinct advantage, to the point that natural selection could coop the feathers and make them more about gliding and less about thermal insulation - the trade-off was worth it.

From there, gliding can become better and better with lighter bones, bigger and more aerodynamic feathers, etc. And from there, you get true flight.

Note: I glossed over the exact origin of the feather. Over the generations, speciation occurred, and new species evolved different scale structures, some of which approached what we now know to be feathers. Just when these filament structures constitute true feathers is somewhat subjective. Wikipedia, as ever, has more.

So do you know which species evolved them first? I'm guessing they were reptilian since: Archaeopteryx has more in common with other small Mesozoic dinosaurs than it does with modern birds. Wikipedia.
which leads me to another question. were dinosaurs warm blooded or cold blooded?