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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 ...

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 ...

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 ...

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, ...

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 ...

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 ...

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 ...

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 ...

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 ...

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 ...

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 ...

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). ...

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 ...

Moles and rats also smell in stereo (Catania 2013 and Rajan et al 2006), as do desert ants (link). The latter is rather interesting, given that ants "smell" using their antennae, which suggests multiple sensory structures, not necessarily nostrils, are required for stereo olfactory ability. EDIT: Hammerhead sharks have two nares and also stereo olfactory ...