Umara,

The biggest observable differences between crocodiles and alligators relate to the plan shape of the head (in general, alligators have a broad U shape to the snout whereas crocodiles have a more pointed V shape – although the Indian Mugger croc doesn’t obey this generalisation!); the presence of a visible 4th tooth in the lower jaw when the mouth is closed in crocodiles (sits at a point of constriction behind the nostrils at the premaxilla / maxilla boundary in the upper jaw); the presence of lingual salt glands on the tongues of crocodiles that appear to work in regulating salinity (but don’t appear to be functioning in alligators) and the presence of Dermal Pressure Receptors all over the skin in crocodiles, whereas, in alligators, the are only located around the jaws.

All of these (and many other) differences place crocodiles and alligators in different families; the alligatoridae, which includes the alligators and caimans; the "true" crocodiles crocodylidae and the gavialidae, which contains only the gharial.

I’m sure that if you look on Google Images you could see lots of examples of the above.

Dave.

Umara,

There is only one 'eel' that produces electricity (and it's actually a species of knife fish). How these fish use electrocytes to produce electricity (and more about them) is nicely explained here: http://helium.vancouver.wsu.edu/~ingall … index.html

Dave.

Chris,

I would think that your lecturers or student advice centre would be best placed to advise you on how to undertake a career in medicine, if that is what you really want to do. As a start though, I'm sure that you would need to think seriously what type of medicine you would want to work in. From there, you could look at colleges that do MSc courses, residency courses or PHd's.

For instance, a quick look at http://medicine.yale.edu/ should give you some idea of what you could expect, in terms of admissions and study programmes.

Hope this helps,

Dave.

Melanie,

Due to the method of feeding for mosquitoes, I think it very unlikely that they would drink blood from a petri dish.

Female mosquitoes detect food sources (i.e. us!) through carbon dioxide emissions from our breath. Once they’ve located a food source, they use heat detectors to locate a suitable place to pierce the skin with their sharp proboscis. They then pump the blood up the proboscis and into their gut.

I’m sure that thinking about this, you can see a number of problems with getting mosquitoes to lap up blood from a petri dish. Just to start you off, think about the consistency of the blood. How will you keep it fluid for the mosquito to be able to drink it (how does one stop it clotting)? How will you attract the mosquito to the blood supply in the first place? (it has been suggested that the large patio heaters that are becoming more and more common may attract more mosquitoes than ‘average’ because of the carbon dioxide they emit, although as far as I am aware, nobody has done any research into this).

Perhaps you could think about how scientists are attempting to control mosquito borne diseases. There are labs that raise mosquitoes, so do a Google search and perhaps find a lab that can give you advice on how they raise mosquitoes.

Best of luck,

Dave.

Skyler,

Here is a short list of the many conservation parties acting within Britain now, many have specialist junior sections, so ask your mum and dad to help you find your local group and get out there!

The RSPB has Wildlife Explorers: http://www.rspb.org.uk/youth/join_in/wex.asp
The Wildlife Trust (for each county, look for your local one (i.e. Cheshire Wildlife Trust, or wherever you happen to live) if you don't happen to be in the East Midlands) has Wildlife Watch: http://www.wildlifebcnp.org/activities-watch.htm
Although they don't really have a junior section, Buglife is a great charity: http://www.buglife.org.uk/
The British Dragonfly Society has projects that everyone can become involved in: http://www.dragonflysoc.org.uk/frameset … e&home
Butterfly Conservation has loads of projects: http://www.dragonflysoc.org.uk/frameset … e&home
RAUK (reptiles and amphibians): http://www.herpetofauna.co.uk/

Good luck!

Dave.

Sara,

A siphuncle is a strand of tissue that runs from the terminal chamber through each of the other chambers and teminates at the back of the living chamber. The siphuncle is primarily concerned with acting as a bouyancy control for the nautilus / ammonite, acting to remove water from one chamber and replace that water content with gases (O2, N, CO2).

The process is almost entirely passive (through osmosis) and occurs when the nautilus has grown a new chamber. This changes the density of the shell and creates  'neutral' bouyancy, where the creature can be suspended in the water at the same depth without the expenditure of energy (so the animal has to swim to move up & down, as well as left & right and back & forth).

Typing "siphuncle" into Google images gave me this: http://images.google.co.uk/imgres?imgur … %26hl%3Den and loads of other pictures. For fossils, the siphuncle is generally lost (as it is a soft tissue) but the holes between the chambers can still be seen (septal necks) : http://www.fossils-facts-and-finds.com/ … led-sf.jpg

Hope that this helps,

Dave.

Just to add to this thread, there has been loads of nice work on taphonomy (the study of burial) that show that the teeth, long bones (such as strong, thick bones like Dave's femurs) and vertebrae (although often with the zygapophyses knocked off) are the bones most often to survive (within the scope of the experiments and within 'real life').

Here is a bit from Palaeonet about taphonomy: http://www.nhm.ac.uk/hosted_sites/paleo … ology.html

William,

Without a very detailed description, or even better, a clear photograph, I'm afraid the answer is not really. Whilst there are numerous flying insects out there, only a few can actually (and would actually) pierce human skin. You've obviously had a reaction to the bite (or maybe even sting, as defence when you brushed it away??) but that doesn't really help as many people have adverse reactions to all sorts of bites.

From personal experience, I can tell you that being bitten by Brachycerids (horse-flies and clegs, often fairly large flies with iridescent eyes) are usually quite noticeable and leave a distinct puncture wound.

Being bitten by the biting midges (generally very small and black to dark grey) Cecidomyiidae, leaves a small red scrape area that often forms (on me at least!) into a raised area around the bite that becomes fairly hard. (http://images.google.co.uk/imgres?imgur … %26hl%3Den)

Although I’ve made mention of the fact that there are ‘only a few can actually (and would actually) pierce human skin’, the few are not really so few, as the variety of different species within the larger groups are often difficult to tell apart in the field. (see : http://images.google.co.uk/imgres?imgur … %26hl%3Den

The above links were from a very quick Google search for horse flies and then biting midges; there is a load to look at. Buglife is the UK charity concerned with all things invertebratey, have a look at them here: http://www.buglife.org.uk/

Hope this helps.

Dave.

Zoë,

I might add that the North American 'yellowjacket' is the equivalent to what we in Britain refer to as a common wasp (Vespula vulgaris). All of the European social wasps (the majority of which have the classic black and yellow stripes) sting as a means of defense, by using a modified ovipositor (egg laying tube) connected to a poison sac. The lack of barbs on the sting (unlike the famous honey bee, for instance) enables the wasp to sting a foe multiple times.

The 'social wasps' form only a very small percentage of the total number of wasp species on the planet, the majority of the rest being parasitic or parisititoid egg layers (laying their eggs in or on host species such as spiders or caterpillars). Again, the ovipositor is modified for the different requirements. Ichneumonid wasps have particularly long ovipositors for boring through bark and wood to lay their eggs on beetle grubs living within, whilst spider-hunting wasps sting and paralyse their victims, drag them to a burrow and lay an egg on the still living spider.

As a short aside, there is a funky wasp that preys on cockroaches. Cockroaches have a ‘scuttle’ mechanism when a light comes on or they’re threatened (quite obviously). However, when attacked by this particular wasp, the wasp stings the cockroach in the thorax and causes it’s front legs to temporarily buckle. As the ‘roach collapses forwards, the wasp stings the ‘roach for a second time, this time using a very precise sting into the ‘brain’ of the cockroach and injecting venom. This turns off the ‘scuttle’ mechanism, whereupon the wasp leads the placid cockroach to a selected hole / borrow, where the wasp lays an egg inside the cockroach. Grisly but very cool! Read more about the experiment to demonstrate this here: http://www.bgu.ac.il/life/Faculty/Liber … .2003b.pdf

In short, the ‘wasps’ as a group have diverse uses for their ‘stings’ but none of the social wasps bite as a defence mechanism and as far as I’m aware, none of the other wasps bite for anything other than prey dismemberment. Here is a brief overview I've just found about Hymenoptera: http://www.sel.barc.usda.gov/hym/overview.html

Dave.

(posted in Mammals)

Dave,

Not convinced about anything you've said about GCG!!! Hatchlings spend the first 3-4 weeks either riding on the backs of the parents or in very close proximity. They aren't really left in reeds either! Great crested grebes are precocial (that is, the young are active a day or two after hatching) and fledge in around 70 to 80 days. Immatures have adult plumage but retain black and white stripes on the head and neck only.

I'd be extremely wary about making inferences about GCG young having striped patternation for camouflage, as for the above reasons, they are not (usually) left anywhere on their own.

My two cents...

Dave.

Hi,

Just to back up Neil, this is almost certainly a Lime Hawk-moth. The similar Willow-herb Hawk-moth is found in Southern Europe and is quite a bit smaller.

As Neil says, many social wasp species will take whatever they can. There are instances of the closely related Vespa crabro (hornet) actively seeking out brown hawker dragonflies (one of the largest British species of dragonfly), then stinging them to death and dismembering the corpes to take back to the hive.

Dave.

Chris,

The calling of the male cuckoo is evocative of the English summer but the population of cuckoos in the UK has declined over the last few decades. There are between 13,000 and 27,000 breeding pairs and these are mostly concentrated around the central and southern areas of England, although there are localised populations throughout the British Isles.

I would think that not hearing a cuckoo until now is likely to reflect the odd start to this year. The plant growing season was rather delayed by the exceptionally dry start to the year, which affects the growth of caterpillars / insect larvae etc. This has a knock on for the breeding times for many passerine species (dunnocks, sedge warblers, reed warblers etc.). The 'host' species brood parisitised by cuckoos obviously need to have laid before the cuckoo can insert its own egg, so this may be a factor in this.

The presence or absence of cuckoos in an area is more dependent on the availability of hosts to parisitise, the more small passerines in an area, the greater the likelihood there will be cuckoos. A drop in host species (may be climate change, food availability, habitat loss etc.) will affect the numbers of cuckoos.

I hope that this helps ,

Dave.

Bruno,

Basically, the current interpretation of the halux (big toe) in A. afarensis is that they were straight and certainly couldn't be opposed. This is really based on reconstructions of incomplete material, so you may see different interpretations based on arguments about how valid the reconstructions are. The post cranial material for all fossils described as A. afarensis seems to show that this creature was an obligate biped, with either functional upper limbs for a partially arborial way of life (long arms, long, curved fingers) or that these are simply 'remnants'  that play no part in a partially arboreal way of life.

As for the footprints at Laetoli, these do not show an opposable halux. They are, for all intents and purposes, as close to being human as if one of us left our footprints on the beach. A. afarensis is still the prime candidate for producing these tracks but that's mainly based on the dating of A. afarensis roughly coinciding with the production of the tracks. With the fairly recent finds for Ardipithecus ramidus and the possibility of finding more for Australopithecus anamensis, A. afarensis may not be the front-runner for long.

Hope this helps,

Dave.

Just to add to the above responses, finger / toe prints aka. dermatoglyphics (on humans, other great apes and also the underside of  prehensile tails of some primates) are formed of keratinous ridges (the same kind of material as nails etc.) that are maintained throughout life. The mechanism for replacement of the keratin cells is likely to be far less frequent than the sloughing of normal epidermal cells (as they are much harder). It may be that the keratin continuously grows (as do nails) at a very slow rate, roughly equivalent to wear. If the dermatoglyphics are removed, through trauma / chemical removal etc., then the fingerprints do grow back to match the 'old' ones, so there must be coding for the positioning of the keratin ridges. I have no idea if any research has tried to identify loci / a locus for this expression though.

Hope this helps,

Dave.

Justen

{Damn, Paolo posted his reply just as I was writing mine, see the overlap!}

Again, we run into the problem of exactly what ‘superior’ actually implies. Superior in terms of general health (psychologically and physically), diet etc. is hard to compare across different HG societies, as well as the myriad varieties within western civilisation.

What is likely is that, for a society such as the !Kung San, meat is a scarce commodity and accounts for less than 30% of the average annual intake. The main subsistence is based on seasonal fruit, nuts and tubers. This may be an indicator towards the ‘base’ diet for later hominids (although isotopic studies from a late Neanderthal showed that this particular male’s meat consumption was equivalent to that of a wolf!). If this is the case, the fairly substantial amounts of meat and fat consumed within a ‘typical’ western diet differ significantly from what we may have evolved to process efficiently.

As for the main body of your question, many extant HG societies (after all, the only ones we have any substantial information on) are, to greater or lesser extents, adapted to their environments. Nilitic peoples (bordering the Red Sea) are generally very tall and thin (low volume, high surface area = efficient heat dispersal), whereas Eskimo nation peoples are often characterised by being shorter and more barrel chested (high volume, low surface area = heat retention). All HG societies are also culturally adapted, they are not just slaves to the environment that they find themselves in, which is quite a large gulf between humans and the majority of other life forms out there.

The idea of primitivism is linked to the idea of the noble savage (coined by Dryden and, perhaps unfairly, more attributed with Rousseau’s ideas on society and human nature). The reality is that, in a western society, in general, you will have a greater fitness (in that the offspring you rear will be more likely, on average, to bear descendents) than that of a ‘primitive’ society. The life expectancy for westerners is, again, much higher than for HG societies, with all the benefits (grandparental care etc) and downsides (pensions, senescent populations etc) that brings with it. If you think about the variety of rather nasty diseases out there that are suffered without the benefits of modern medicine, being a lion’s dinner would often seem like a better choice! (in my book…)

Reverting to HG methods for living, within a western society is pure romantic fantasy, linked with the above. Without a huge (and I do mean huge) amount of human mortality, there simply aren’t enough resources to be hunted and gathered. There are reasons why there are only small numbers of HG’s today (although I’m not      talking about the marginalisation of most populations due to agriculture etc.), in small, often nuclear units. Each ‘tribe’ has a carrying capacity, as do populations of almost every other creature, which is dependent on the amount of resources that can be utilised in the local area vs. effort for gathering.

Cheers,

Dave.

Muzzammil,

I'm sure that if you think about this one, you can work out the basic procedure on first principles. What would you do if you came across a plant (or any living thing) that you thought was undescribed?

First, you'd have to make sure that it was undescribed, which means a detailed study of it's anatomy, DNA sequence etc, gathering as many points of information as possible. You would then have to cross-reference with all the rest of the described plant species in the world. This may be extremely time consuming, or you may be able to say Species X has umbilifer 'flowers', therefore, it is likely to be an umbilifer (and thus discount the rest of the plant families). You could then concentrate on looking at the umbilifers to see if there are any species within that group that look very similar to Species X. Through this means of comparative study, you should be able to work out to which other species your Species X is most closely and thus arrive at a name (perhaps it is very closey related to wild carrot Daucus carota, Species X would then be likely to be given the generic name Daucus and a specific epithet relating to the discoverer, a distinctive part of the anatomy etc etc.). The venerable (and completely unintelligible) tome on the International Code for Botanical Nomenclature would have to be consulted to ensure that the name and description for this new species were recorded in an appropriate fashion.

Hope this helps,

Dave.

Joon,

Congratulations on submitting the longest post so far... ;>)

Without reading the full paper, it is difficult to give you a definitive interpretation of the paper. I also have no idea how much you know about the subject!

In short, however, the article is suggesting that the ramus (the ascending part of the jaw that hinges underneath the ear) in Australopithecus afarensis is very similar to that found in extant gorillas. This suggests that the ramal morphology (the shape of this part of the jaw) is too derived (adapted for a reason, in this case it is likely to be related to the diet of these species) for A. afarensis to be the ‘common ancestor’ for the rest of the hominins (the group of human like primates possibly evolved from this species).

In general, the postulated common ancestor for humans has shifted around quite a bit over the years but, in general again, the more ‘general’ body plan is seen to be the most likely to be the common ancestor.

If it is demonstrated that in A. afarensis this is more derived feature (linking it to A. robustus and possibly the rest of the robust apiths – the synapomorphy noted in the 3rd paragraph), then it is unlikely that other human like species evolved from A. afarensis, as they would have to re-evolve the ramal morphology as shown in Ardipithecus ramidus / chimps. If this is the primitive condition, it has higher potential to be moulded through natural selection into several different shapes, whereas, if the ramus is already specialised (as for the gorilla and robust apith morphocline – a set of Australopithecines with huge jaws, probably for eating tough nuts etc.), it is much less likely that it evolved from thin, to very broad and then back to thin.

I hope that this helps somewhat, I’m afraid that my explanation may be as confusing as the article!

Very short answer, this may show that A. afarensis is too specialised to be the common ancestor of later hominins!

Do get back to us if you have further questions.

Dave.

Charlie,

Not that we here at Ask a Biologist would condone the launching of spiders (or anything else) out of windows, even in the name of science, I have to say the spider would almost certainly survive.

This is related to the fact that spiders are not heavy (even large ones), so even though, all thing being equal, everything will accelerate at G (the gravitational constant 9.8m/sec/sec), they are much less likely to go splat than a heavier object. Secondly, if thrown onto a garden, the grass will provide a much softer landing platform than, say, concrete.

Third, and most importantly, spiders (and most other leggy terrestrial inverts), have a high surface area against volume. This means that they have a large surface to act as an aerofoil and thus slow descent (much as cats spread their legs when falling from heights, or think of a feather floating down) against a small volume (and in this case we can think of this as equating to mass). So, low weight in addition to high aerofoil properties means that a spider ejected from your premises in such a manner will (should) survive.

Hope this answers your question.

Dave.

Linking in from Dave's post about unfertilised chicken eggs and caviar, can someone please explain to me how and why chickens lay unfertilised eggs? (There was a recent thing in the British press about a young girl hatching two ducklings from organic eggs).

Why do they go all the way through the energy requirements for producing an egg and coating it with a shell (using the calcium and phosphate resources from their own body to do so) when there is no end product?? To do so is deleterious to the chicken with no gain.

Is there something ridiculously fundamental I'm overlooking??

Dave

Helen,

Aside from the usual cliches about mantids and black widows engaging in cannibalism during mating, there are numerous other examples. There was a recent study (2001) of kin selection cannibalism amongst subsocial spiders (abstract here: http://www.ingentaconnect.com/content/b … /art00346) and one on wolf spiders (2006), abstract here: http://www.blackwell-synergy.com/doi/ab … 6.00770.x.

There is also a spider (who's name I unfortunately can't recall!) where the mother guards her eggs until they hatch and then presents the underside of her cephalothorax (the fused head and body segments) to her offspring. She almost forces herself to be eaten by her own offspring! In this fashion, her DNA is still continued, whilst helping her young get a hearty meal before making their way into the world.

The reason for cannibalism (within non-human animals) is likely to be a relation between food (prey)availability (how many prey animals there are within a particular area) and competition. The most competition animals face for resources are from animals that have similar adaptations to exploit those resources, therefore elimination of the competition frees up those resources for an animal and its progeny, as well as providing a tasty snack (no point in letting energy go to waste!).

Hope this helps,

Dave.

Adam,

A very interesting question and one that is of importance to many conservationists working in Britain.

One of the major projects for conservation in Britain is the restoration of lowland wet grassland. Lowland wet grassland is of prime importance for many breeding waders (snipe, lapwing, redshank etc) and for some species of wildfowl (gadwall, shoveler, teal etc). The conditions required for breeding differ between the species and so when managing lowland wet grassland for waders and wildfowl, conservationists need to take into account the variety of mosaic habitats needed for breeding, as well as available food source, particularly for the young.

During spring and early summer, we need to keep the water tables high on our grassland. This enables waders in particular to probe muddy margins for food, mainly earworms and leatherjackets (the larvae of Tipulid (crane) flies). The high water table means that these inverts migrate towards the ground surface, making them easier to reach by the waders. We retain a high water table until around mid June, through sluices, we then lower the water levels so that the ground dries and we can manage the grassland in August or September

During the winter months, a flood event on the grassland can be extremely beneficial in controlling plant regrowth (particularly rush species), it is also great for dabbling ducks, as many seeds are washed out. However, if the flood lasts for more than a couple of weeks, this can have severe consequences on the invertebrate populations of the grassland. Generally, worms and the larvae of flies and beetles will migrate towards higher ground as soon as the ground becomes too wet for them. The rate of movement is, as you’d probably imagine, not particularly quick but enough for many individuals to survive. With a short-lived flood event, the animals will migrate back down and recolonise the vacated area. This will take up to about 3 weeks from the end of the flood. With a longer flood event the ground will obviously take longer to dry but the food sources for the worms and larvae will have been removed, as well as high mortality for many slower individuals. If this is the case, it can take upwards of 6 months or more before the affected area is roughly back to normal.

It is therefore of vital importance when managing lowland wet grasslands for conservation (of birds, mammals and the invertebrates and plant communities that support them) that we manage water levels correctly, keeping them fairly wet but not flooded over the winter, maintaining high water levels in spring and then dropping them in late summer.

I hope this answers your question, in a round about kind of way!

Dave.

(posted in Plants & Fungi)

Joakim,

This sounds like an excellent project to undertake yourself! The quick answer is I don't know and I don't know if this has been undertaken experimentally. Any one out there??

On many broadleaved deciduous trees, the shedding of leaves is regulated by the availability of day length. During winter periods, when daylight is at a premium, to have large floppy leaves using up lots of energy is not in the best 'interests' of the tree. The trees thus create a 'plug' of cells at the base of the leaf that gradually closes off the phloem (the fluid conducing tubes within a plant). This means that the sugars trapped within the cell will degrade and promote the production on anthocyanins (the reddy pigments to cranberries, strawberries etc.). At the same time, the production of chlorophyll (giving the leaf its green colour) stops.

Once the phloem are fully plugged, the leaves become dominated by the decaying sugars, anthocyanins and caretenoids (yellow and orangey colour producers for bananas, carrots etc.), thus changing colour. The changes in relative amount of these three causes the changes in leaf colour through the period until leaf drop.

Thus, if you could take a tree / shrub, induce the first stages of phloem closure and then control light levels such that the phloem either don't close fully or re-open, thereby not restricting sugar access and egress and staying the cessation of chlorophyll production, you may well be able to revert the leaf to its chlorophyll colouration.

Let us know how you get on, if you try this experimentally!

Dave.

Hi Joanna,

Although Neil is correct as regards the specifics of your question, I can tell you that there are numerous species of insect (many in the family Hippoboscidae, which are a part of the Diptera (fly) order) that are obligate parasites of mammals and birds. Here is a link to some nice pictures of an Ornithomya bird parasite:
http://images.google.co.uk/imgres?imgur … %26hl%3Den

From personal experience of being bitten by these critters (whilst cleaning out old bird nests), they leave a small puncture wound, whereas flea bites tend to have a small puncture with a ring of spots around (hence the old nursery rhyme 'Ring 'o Roses).

As to these parasites getting into the clothes on the washing line, I think this is rather remote, many of these types of fly are fairly host specific and are unlikely to feed off humans unless it is very opportune for them to do so (by hitching a ride in my clothes, for instance!). These flies feed on blood whilst in their adult stage, there are larvae of other parasites that live in the nest that feed on blood.

If you plan on doing anything about the bird nests, I would recommend rubber gloves, no loose clothes (close sleeves etc off.), wear a breathing mask and pour boiling hot water onto the nest before touching it.

Hope this helps,

Dave.

Brysen,

There was a particularly famous body recovered from near the border between Austria and Italy in 1991. Nicknamed Otzi (or Oetzi) he was dated to around 3,300BC. A short Google search for Otzi leads to http://www.crystalinks.com/oetzi.html.

Mammoths, in particlular, have been recovered from ice sheets, a baby one around 10,000 years old even being eaten by the finders' dogs!

As for cloning, it may be possible, depending on the condition of the tissues. Being frozen in ice for several thousand years leads to a state of mummification, where the body is dried out. It may be possible to extract portions of DNA from the skin or even bone tissues and amplify it (through PCR etc see the Not Just a Labcoat essay on sequencing http://www.askabiologist.org.uk/labcoat … dna.html).

For Otzi, part of his DNA was extracted http://news.bbc.co.uk/1/hi/sci/tech/4674866.stm from his stomach.

Hope this helps.

Dave.

Sarah,

In answer to question 2 first, yes, many other animals change colour, some in very short periods of time (cuttlefish, squid etc. are brilliant at changing colours in rapid succession) and some that take a bit longer (plaice, flounders and other bottom dwelling flatfish often match their surroundings very accurately after a couple of minutes or so).

The pigment and light reflecting cells in animals (mainly cephalopods like the squid, fish, reptiles like the chameleon and amphibians) are called chromatophores. For animals like cuttlefish and squid that change colour rapidly, either to hide / sneak up on prey (known as cryptic (this simply means ‘hidden’) camouflage) or to signal to a mate / rival etc, this is known as physiological colour change and is controlled by muscles around each chromatophore squeezing and distorting the shape of the chromatophore (a bit like the muscles around the eye squeeze the lens to enable us to focus).

Chameleons change colour through a rather different mechanism, which has far more to do with cell signalling (this is part of a complex system of communication that governs basic cellular activities and coordinates cell actions), so chameleons change colour as a result of mood (anger, mate attraction etc.), rather than to blend into their background.

The way in which chromatophores are pigmented and control this is rather complex. A quick scan of  this article http://en.wikipedia.org/wiki/Chromatophore seems to be fairly accurate but it may be a little complex for you. Have a look anyway.

Best wishes,

Dave.

(posted in Mammals)

Micheal,

Interesting people you meet on swimming courses!

Anyhoo, the Mammalian Diving Reflex and the closely related Gasp reflex are not, unlike the way it was explained to you, a way mammals can breathe for extended periods underwater. As I’m sure you are aware, all mammals must breathe air, even the marine ones, underwater, all mammals must hold their breath.

What happens with the MDR is that it acts to conserve oxygen when the body is immersed in water. This happens in three key ways;
1)    the heart rate lowers (known as the bradycardial response);
2)    a restriction of blood to the arms and legs (peripheral vasoconstriction), instead sending the blood to the vital organs (heart, lungs and brain) and;
3)    the blood concentrates, through peripheral vasoconstriction, in the thoracic cavity (the area of the torso between the neck and the diaphragm) to resist water pressure.

It appears that the effects of MDR / Gasp reflex kick in in humans with more effect if the water temperature is under 21oC, hence gasping if you jump into cold water!

As to whether humans can do the same thing, well we can and do. I’m sure you’ve heard about people falling into icy rivers and whatnot and surviving without oxygen for far longer than if they would if they were to be without oxygen on land. It also appears that, through rigorous training, people can consciously undertake the three actions above. People that freedive immediately spring to mind.

Marine mammals utilise the MDR in ways so that they can stay underwater for far longer than humans could, they do this by controlling the amount of myoglobin (when haemoglobin is shifted into use) in their in muscles.

I hope this helps with the swimming.

Dave.

(posted in Mammals)

Hi Mila,

Seals and sealions belong to the order Pinnipedia (‘fin foot’ and these are divided into 33 species, belonging to 3 families. The Otariidae contains 14 species, including the fur seals and the sealions. The Phocidae are the ‘true’ seals and have 18 species. The third family is the Odobeidae, which is the walrus.

In answer to your question, the Otariidae (sealions) have external ears, which the Phocidae (‘true’ seals) lack. Perhaps the most obvious difference between ‘true’ seals and the sealions & fur seals is shown when these animals are on land. The ‘true’ seals have their hind limbs modified into hydrodynamic flukes (these provide a ‘rudder’ mechanism when the seals are swimming). However, so adapted are the hind limbs for life in the water, they can no longer support the body weight of the animal on land (their pelvis (hips) doesn’t provide a stable support for the remains of the legs). The hind limbs for the fur seals & sealions are also adapted for life in the water but when on land, they can rotate their hind feet forward to support the body. This means that these animals can almost ‘run’ when on land, whereas the ‘true’ seals have to flop along (known as gallumphing!) on their bellies to move.

I hope this helps,

Dave.

Ben,

I agree that the Urey-Miller experiment was cool and yes, over time it has been thoroughly questioned. They managed to create 13 of the 22 amino acids that are used to build proteins. I'm not sure what the creationists have had to say about the initial experiment but more recent experiments have shown that amino acids, hydroxyacids, purines and pyrimidines can all be created in these ‘test-tube’ conditions.

Major objections to the initial experiment centred on the amount or composition of molecules within the atmosphere, the destruction of certain molecules by Ultra Violet radiation and the reduction of molecules by oxygen.

As far as I am aware, the current consensus is that the Urey-Miller experiments were pretty valid, they have been run repeatedly with different molecules (based on different calculations on the composition of the prebiotic atmosphere) and under different conditions.

Therefore, I would say that:
1) Yes, the experiment (and more recent ones) are important,
2) Yes, the question does matter. Where life come from is a big topic for biologists.
3) Yes, there have been more recent experiments (a quick search on Google Scholar lead me to Springer Link, where you can register to read articles http://www.springerlink.com/home/main.mpx), search their pages.
4) Why do some argue against it? This is a much trickier question. First is that scientists want to be as accurate as possible and new theories or interpretations of results or experiments further scientific research. On the other hand, if you are talking to creationists who question the validity of the experiments, they are likely to have a different agenda than the pursuit of rigorous scientific research. The creation of basic amino acids is a start on the road to life, it is not the creation of life per se.

Finally, can you argue against people that say it doesn't prove anything? Yes, but you will need a firm grasp of the initial experiment and subsequent work. Further research is required, I’m afraid there is no easy answer for this one!

Dave.

Further to Alistair’s post above, although he is spot on with the relative amounts of solar energy reaching Earth through the various cycles of precession and obliquity etc., there is also thought that the degree of these are affected by the position of the continents.

Since the verification of the theory of continental drift by the mechanism of plate tectonics in the 1960’s and 70’s, a greater understanding of paleoclimates has been possible, through continental position, ice and deep-sea sediment cores and glacial deposits (till, moraine, striations etc.)

What appears to be shown is that where the continents are (or were) leads to the formation of glaciations. Because the sea has a higher heat capacity that the land (it takes four times longer to increase the heat in an area of water that the same area on the land and, conversely, four times longer to lose that heat) it has a relatively stable temperature. Interruptions or reductions to the movement of this 'stable' temperature water around the globe, from the warm equator to the cooler poles, is thought to lead to the formation of ice sheets. Think of how the Gulf Stream (the North Atlantic Drift or Conveyor, which brings warm, wet weather from the Gulf of Mexico to Britain and Irelend), enables palm trees to grow on the Isles of Scilly and Devon and Cornwall, up the west coast of Britain to Arran off Scotland, whereas, across the Atlantic but at the same latitude, Newfoundland is extremely cold. Without the NAD, Britain would be very much colder (and probably drier!) than it is today, much more like eastern Canada.

Land masses at the poles (as Antarctica is at the moment), a land locked pole (as the Artic Ocean is today) and the position of a supercontinent (Pangea or Rodinia in the dim and distant past) all reduce or restrict the flow of water around the globe. This causes ice sheets to form and positive feedback (in the form of albedo reflection and others) to create ice ages, of which the orbital cycles are likely to feed into.

The Paleomap Project: http://www.scotese.com/climate.htm, gives a nice representation of past continental position and relative temperatures.

Dave.

(posted in Birds)

Hello Rudi,

I feel a bit sorry for the worms too! Unfortunately for the worm, minding its own business eating and moving within the soil, the way that it is made up, of muscles to move and water within it to help it live, these are the same kinds of thing birds need as well. The birds get a lot of the things they need to live easily by eating the worm. This works the same for us Rudi, by eating meat (it may be a beef burger for us, rather than a worm!) we can easily use the goodness within the burger to help us grow and run around.

Creatures that only eat plants need to eat a lot more and have it within their stomachs for a long time to be able to use it to keep living. Meat is much easier and quicker for animals to digest (to breakdown within the tummy), because it is very similar to the way in which many creatures are already made up.

Dave.

(posted in Mammals)

Hi Jennifer,

Right, a few questions there!
Starting at question two, yes, they do need water!
Question four: why do you need so much water? Water is a vital part of the make up of living things, for lots of very important reasons. Suffice to say that water is a large component of protoplasm (the 'living' bits of chemicals inside all cells), it is an almost universal solvent (lots of things dissolve in it) and lots of other things including its density, thermal properties etc. Many of these can be found in standard biological texbooks.

On to your marine mammals...
The Cetacea and Pinnipedia (whales & dolphins and seals & sea lions) are secondarily marine, that is, they have moved from the land back into the water. As you know, life began in the sea and as such, some creatures evolved their bodily functions to be isotonic (having the same concentration of salt in the blood as there is in sea water), these include hagfish and the cartilaginous fish (sharks and skates etc). Bony fish (teleosts) like makerel are hypotonic, that is, their blood salt level is lower than that of seawater. Teleosts drink seawater but also gain the salts contained within in it. They deal with the excess salt by excreting it back into the water by using chloride cells in their gills. The control of water within living systems is called osmoregulation.

Marine mammals are also hypotonic; the main problem in these animals is gaining salts from their food and any seawater accidentally ingested whilst feeding. These animals are able to deal with this by having kidneys that can produce urine that has a higher salt concentration than the blood, which allows them to excrete excess salt in the urine. Whilst the kidneys of marine mammals are extremely efficient, they also minimize their salt gain by not drinking seawater. Instead, they get all their water from the food they eat. The efficiency of their kidney is reserved for producing highly concentrated urine, which allows them to conserve their water.

So, marine mammals have evolved a way to obtain water from the foods they eat and they have an extremely efficient way of concentrating the salts into the urine they expel.

I hope that this helps you understand how marine mammals survive without drinking fresh water.

Dave.

Gemma,

Further to Neil's answer, there are two major (and competing!) answers to this:

1) "out of Africa II / Replacement (the most popular at present) - Human beings sensu stricto i.e. Homo sapiens ("us"!) are first defined from African deposits that are dated between 100 & 200kbp (thousand years before present), the most famous site being Kleises River Mouth in South Africa.

It is postulated that these, as they are termed, anotomically modern humans (there are major cultural differences from Cro Magnon man, where "human" culture seems to develop at around 40-35 kbp in France) spread throughout Africa and then the whole world over the next 60 to 80 thousand years. They are dated roughly from Australia from about 60 kbp, and Micronesia and onwards over a long period of time, getting to New Zealand only about 1100 years ago. The Americas are a matter of contention (as most of it is) but it seems likely that a population from around Lake Biakal crossed over the Bering Land bridge (between Siberia and Alaska) during the last glaciation and down through North America (there are classic Clovis (a stone tool culture) sites dotted all over North America from around 13 kbp) and then onto Argentina, where some fossils are dated at around 11 kbp but,  there was some real doubts over the veracity of aging of the deposits.

2)Regional Continuity model / Candelabra, as espoused (mainly) by Milford Wolpoff. This states that the evolution of modern humans occurred as a result of genetic mixing between regions, so that, for instance, the initial 'prehumans' in China (Homo erectus) were not replaced by AMH (anatomically modern humans) but rather there was a 'continual' flow of genetic material between neighbouring regions (west through Pakistan to Georgia) and those regions, swapping DNA with western Europe and Africa up until the present.

Specimens from Australia are the causing the most contention at the moment due to their similarity to current Aboriginals. There are also large question marks over the reliability of mtDNA (mitochondrial DNA, inhereted soley along the maternal line).
With this theory, human beings ("us") are very recent due to the continued migration and evolution of humans over the period of time when Homo erectus (or Homo ergaster) left Africa around 1 million years ago.

The following are some links that provide more detail of the current debate over human origins:
www.actionbioscience.org/evolution/johanson.html
www.bradshawfoundation.com/notafrica.html
www.killgrove.org/ANT210/modernhumanevolution.doc
http://pcwww.liv.ac.uk/~gowlett/
http://www.nhm.ac.uk/nature-online/life … index.html