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12

There seems to consensus that it is not competition for tall food. Giraffes actually often feed on resources that are lower than their maximum possible height. See: Simmons, R. E. & Scheepers, L. 1996. Winning by a Neck: Sexual Selection in the Evolution of Giraffe. The American Naturalist 148: 771–786 This paper put forth the idea that sexual ...


12

Cat claws are growing all the time, like horse hooves, or human nails. However, cats and horses usually use their claws/hooves, so they get shortened through mechanical action. An indoor cat may need their claws trimmed if it doesn't use them enough (that's why cats will want to scratch everywhere), or if has supernumerary toes that don't normally touch the ...


10

A recent paper called 'Genetic Influences in Sport and Physical Performance'[1] states: "Muscle fibre type determination is complex. Whilst initial composition is likely to be strongly influenced by genetic factors, training has significant effects on fibre shifts." They also go onto say that: "However, the role of genetic variation in determining ...


10

First, I think it worthwhile considering 'Why would internal symmetry be beneficial?' Developmental simplicity jumps to mind immediately. You can also consider relationship to external organs; the stomach and esophagus are lined up with the mouth which is symmetrical about the sagittal plane. Or maybe even balance; the lungs are large organs and if put to ...


8

While it might make more logical sense to have separate passageways for air and food/water, this did not happen in evolutionary history due to the peculiarities of lung development. Vertebrate lungs develop as an outpouching of the gut tube, which itself has a very long evolutionary history (probably homologous among all deuterostomes). In the image below, ...


8

At the very least, I know that male primates also have nipples like female, though they are very close relatives to human. On the other hand, in some of my dissection labs, I noticed that male pigs also have nipples just like the female ones. It seems to be the case that most male mammals have nipples, which probably has to do with mammals being ...


8

Perhaps what your teacher meant was not so much a difference in Leydig cell morphology, but in interstitial tissue morphology, ie. tissue which occupies the space in between seminiferous tubules. Leydig cells are its most interesting component, others being small blood vessels (a lot of them), nerves and connective tissue (mostly fibroblasts, mastocytes, ...


7

Oxygen levels have changed greatly throughout Earths's history starting with very little atmospheric oxygen and gradually increasing as photosynthetic activity appeared until all the oxygen sinks such as minerals had been filled, then taking off, reaching as high as 35% of the atmosphere during the carboniferous period 3. The reasons behind this sudden ...


6

I have studied all available (via University library) literature on the Leydig cells and I think your teacher might have this article summarizing the morphological studies on Leydig cells in different animal models in mind. To put it straight, the most common animal models for studying Leydig cells are rats, mice and pigs. The development of Leydig ...


6

Building on the answer given by Sean Connolly above, it would be very easy to imagine evolutionary scenarios where organs are more likely to develop asymmetrically than symmetrically. For instance, imagine an organism that has a simple digestive system that consists only of a single undifferentiated intestine that runs directly from mouth to anus in a ...


5

Most mammalian males have nipples. The duck-billed platypus does not have nipples but you begin to see development of nipples in marsupials (Park and Lindberg 2004) like the opossum and kangaroo. Development of a complete nipple begins in the eutherian (placental) mammals. The mammary glands develop early in the embryo along a pair of ridges called the ...


5

I'd suggest that one factor could be the difficulties of breathing water - it is highly inefficient. The following is a summary of this response to a TREE article. Fish spend 10-30% of their energy on breathing because it is so inefficient to use gills because diffusion rates are much slower and oxygen is less abundant. Gills grow in proportionate scales to ...


5

I would argue that the orbiculares do have antagonists. To some extent, levator palpebrae superiorus antagonizes orbicularis oculi, and zygomaticus major/minor as well as risorius antagonize orbicularis oris. I can think of three muscle that don't have obvious antagonists: Stapedius Tensor tympani Articularis genu 1 and 2 essentially perform the same ...


5

Mantis shrimp use their first maxillipeds for grooming (maxilliped=modified appendage), which is specialized for this purpose. Details and a picture of the organ can be found in the link. The second maxilliped is their famous specialized organ for striking or spearing prey with enormous force. More about their raptoral appendage, with links to further ...


4

I suspect it is just physics. Each of your legs makes up about 1/6 of body mass, leaving about 2/3 of your mass superior to your hips. Raising one leg requires action of the hip flexors (i.e., iliopsoas complex) but also activity in the anterior abdominal wall muscles (rectus abdominis, obliques) and back muscles to stabilize your abdomen. To raise the ...


4

They don't have to -- there are times in life of a bacteria (cell division, hunger, mutations, attacks of lysozyme and other enzymes, cell lysis) when any possible antigen gets less or more exposed. About escaping phagocitosis, there are numerous strategies to achieve it -- from forming a large slime-covered colony, through killing or disabling phagocytes ...


4

It would appear that at one time it was thought that a 'gap' in the skeleton of a Stegosaurus was a space for another brain. This is now thought to be a storage space for extra food. Googling your question brings up a number of answers along this line; http://en.wikipedia.org/wiki/Stegosaurus#Second_brain ...


3

A brief study I conducted of my peers (10 people of varying genders, ages, and races, all about average body type) revealed a rather consistent foot-to-leg length ratio of 1:3 for males and females (variance is insignificant), and width of 2:3 for males and 1:2 for females.


3

This is a fascinating bit of genetics. Dogs are especially variable in size and many appearance, behavioral and temperamental phenotypes. It was long expected that variations in developmental genes were the reason that dog breeds were responsible for the amazing flexibility of dog sizes. One early locus found was IGF1 (insulin like Growth Factor 1). ...


3

It isn't just humans that have fused sacral vertebrae. Animals on the phylogenetic tree ranging from Squamata (lizards), to Aves (birds), to even Monotremata (egg-laying mammals) all have fused sacral vertebrae. The fused vertebrae can serve as a stronger, weight-baring structures for animals that do land locomotion, including humans. Any bones that have ...


3

It's a general phenomenon that the time scale correlates with the size scale of complex systems. Energy consumption is the main concern dealing with the speed for biological organizations. In the absolute sense, a turtle has a higher speed than a small bug. But based on their sizes, the bug seems much quicker and faster. So we need to normalize the speed ...


2

You can try Biomechanical models used in software frameworks such as OpenSim. Here is an example of a combined upper and lower body model in XML: ULB_Project.


2

This is quite a hard to answer question. There are different cell cycle molecules that, if mutated or knocked out, have shown to cause the cell to have a different shape or "overgrow" in size or not grow at all... You might find some insight here. There are lots of factors that influence cell size and shape, thus it is a very complex system to study. For ...


2

You say "snout" but you might more specifically mean "muzzle" if you're focusing on the teeth aspect. Ram Manohar M hypothesizes some good reasons that make sense but for some other examples of snouts, here's a fun link that describes a few uses: Tapir: "nose and upper lip form a trunk he uses to grip, handy for grabbing and cleaning branches and plucking ...


2

Obviously there is an evolutionary advantage for those animals which has a long snout/muzzle. That is why they are still around. For carnivores the canine is the most important tooth and it is positioned strategically at the front corners of the jaw. Canines are meant to pierce and is essential for holding on to the prey and preventing from escaping. They ...


2

I'm impressed to stumble upon someone who can do that with his tongue. And mainly because I can do that myself! Looking at the images and feeling with my tongue, this rugged area you mention is definitely too close to the nose to be the adenoids. So I googled a bit (well, more like a lot) and I found this cool webpage which details that area. ...


2

It's not clear what "proximal" means in this context. It's not a standard use of that anatomical term in English. I'd also say that the figure on the left actually does show the pectoralis major. The author of this figure might be trying to show the muscles that cross the proximal joints in the upper and lower limbs. For example: Upper limb Pectoralis ...


2

It is, indeed, the alimentary canal. It is actually this canal that it's important for one to remove when "de-veining" shrimp, rather than the vein itself, which lies immediately dorsal to the digestive tract. In the future, I might suggest doing a little more research prior to asking the stack exchange, as frequent users of the site do like to see ...


2

I think it depends on hunger, preferences.... Domestic cats can pretty much eat it all. They might discard items they can't digest like fur, relatively large bones... other than that what they leave behind is rather individual. I'm guessing this cat doesn't like salads. Typically I haven't seen hunting cats discard digestive organs. Aside from fur and ...



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