h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

I've been reading about the nautilus and had a few questions. Are the "nautilus" and the "ancient nautilus" the same thing? Also, I read that I has a retina, but no lens. I'm afraid my biology teacher was much too interested in plants to explain to us anything about the eye. I was wondering if you could give me some information on how the eye works, and what this is indicative of in the nautilus.

Thanks much.

First, there's the currently living animal 'Nautilus'. Then there are closely related fossil animals which belong to the same sub-class 'Nautiloidea', which I suppose may be referred to as 'ancient nautilus', but would probably be better called fossil (or ancient) nautiloids, to avoid people assuming that all fossils are exactly the same species.
(There are also the extinct Ammonites, which do have similarities with nautiloids, but are considered to be more distantly related than it might at first appear.)

Regarding the Nautilus eye, there is no cornea or lens, and therefore no focussing of light, but since there is a very small aperture, the overall effect is similar to a pinhole camera. Since the aperture is small, the image on the retina is dim. Increasing the aperture size to increase the amount of light captured would result in a brighter but less well-focussed image.
(Anyone with vision requiring correction can observe the pinhole camera effect extremely easily by poking a ~1mm hole in a piece of card or dark paper, closing one eye, and looking the hole with the other eye (without glasses/contact lenses) at something that would normally be blurred)

The only thing *required* for an animal to have some kind of vision is a collection of nerve cells sensitive to light, so there will always need to be some kind of retina, or more primitive sensory patch.

(If you stick "nautilus eye retina lens" into Google, the match entitled 'Lecture 17' may show things better than I can explain here

Thank you very much. I would have written back sooner, but my internet service is down

#^#$%*!

I'm wondering if you would take a look at my rewrite. I have taken great pains to avoid scientific errors, but I'd appreciate your examining it just in case.

http://www.bbc.co.uk/h2g2/guide/A655805

Thanks.

Josh,
I'm a little busy right now, but will try to give it a proper read in a couple of days.
Dave

Regarding the lack of transitional species, it depends immensely on how you define 'transitional'. (I think I wrote something about that earlier.)

Fish ->Amphibian: It wouldn't be surprising if transitional fish-amphibian species were hard to find. Adapations that give creatures access to whole new environment are likely to be rapidly driven to some kind of conclusion, with initial transitional species rapidly developing into, or being overtaken by, later species.

Amphibian-> Reptile:
Regarding the metamorphosis, it's not of the same nature as the change from caterpillars into moths. Legs and lungs grow, tails and gills are reabsorbed. All the while the developing creature is capable of feeding and growing, which is its purpose, since it developed quickly from a very small egg.

Reptile eggs are covered in a leathery material, not a hard shell.Given that they develop out of water, the animals which emerge from them must be sufficintly developed to move, survive and feed on land. The eggs are much larger and less numerous than amphibian eggs, and there is no evolutionary pressure to develop any primitive or intermediate form to obtain food before the production of the final form, since the food is within the egg.

Mammal->Reptile
'Douglas Futuyuma writes, "The gradual transition from therapsids to mammals is so abundantly documented by scores of species in every stage of transition that it is impossible to tell which therapsid species were actual ancestors of modern mammals." But Darwinian transformation requires a single line of descent, so large numbers of eligible candidates prove nothing.'

That seems a very odd statement from someone who earlier said :

'If species are continually mutating, never constant, why do we continually find several of the same, certain prehistoric creatures, but never any that appear to be in transition'

"... If [the evolutionary] hypothesis is that mammals evolved from therapsids only once...then most of the therapids with mammal-like characteristics were not part of a macroevolutionary transition. If most were not, perhaps all were not."
Isn't logically sound.
If someone pointed at a house and said 'my grandparents are in there', and I went and looked in the house, saw dozens of people, and went back to the person and said 'There are many people in there who are not your grandparents, so I doubt your grandparents *are* in there, they'd think I was an idiot.
If they'd told me 'All the people in the house are my grandparents', it would be a quite different matter, but that isn't what evolutionist say about fossils.

Apes->Humans
(I've already mentioned that much anthropology should be taken with a large pinch of salt)
Homo erectus fossils are found in Africa, so there is no conflict whatsoever between descent from Homo Erectus and the mitochondrial eve theory.

Changing Java to Nebraska in the Nebraska man section hasn't altered the fact that non-African hominid fossils really aren't of central importance to human evolution. Their only real significance lies in the light they may throw on the question of whether successive waves of developing hominids spread out from Africa and replaced their predecessors completely, or whether some ancient adaptations external toAfrica were incorporated into the populations, and have survived to the present day.
If this section is to stay in (which I'd sya is a bad idea), it really should be incorporated into the human origins section.

Dawkins/Finch beak size has already been covered elsewhere. Nothing about what Dawkins said contradicts evolution (quite the reverse), denies facts, or is connected with any kind of hoax.

Regarding the eye, the evolution of the different eyes multiple times is actually strong evidence *for* evolution. A designer would presumably re-use designs, rather than creating lots of different ones. What mutliple evolution does show is that the selective advantages of having visual perception are enormous.
Also, many partially flying animals do exist.

I tried to explain sexual selection once.

Typo - Anthropic Principal should be Anthropic Principle

Free protons either don't decay, or deacy at an incredibly small rate. Free neutrons decay to form a proton, electron and antineutrino in an average of 10.3 minutes.
When confined in an atomic nucelus, neutrons and protons are both generally stable, but it is possible for each of them to change into the other. (with the appropriate generation of balancing particles)
Looked at from the perspective of the neutron being electrically neutral, and given that an isolated neutron can decay to form a proton and an electron, the balancing of electrical charges isn't surprising.

The orbits of most planets are roughly circular (excluding Pluto)
Orbital eccentricities :
Mercury .206 Venus .0068 Earth .0167 Mars .0934
Jupiter .0485 Saturn .0556 Uranus .0472 Neptune .0086

Water isn't the only substance in the universe that is less dense in solid form rather than liquid form. Antimony (as well as some other metals and alloys) expands on cooloing and solidifying. That doesn't mean water isn't very special - the fact that it's liquid in the temerature range it is, or its large specific heat capacity are possibly as significant.

That's about all I can manage at the moment.

While much has been added to the article, it does seem like comments made earlier by othe people haven't had major effects in terms of modifying sections that were confusing or contested.