Why do men have nipples?

Junior D

I have a couple of questions here:

Why do men have nipples?

Why do people yawn?

Why can't we get the full use of our brain?

Why can't the human body digest cellulose?

GLaDOS

Nipples - Men have nipples as when we develop in the womb we are essentially sexless for a while, and the female body is used as a template of sorts, before hormones kick in and give us our manly bits. At this point the nipples have already been formed.

Yawning - I believe this is an attempt to get more oxygen into your body when it's tired to try and revitalise it. Somebody may correct me on this though.

Full use of brains - No sure what you mean here, the old "only using 10% of our brains" is a myth.

Cellulose - We can't digest cellulose because it is a very tough material with many cross links, making it difficult to break down. As a result our digestive system doesn't hate the power to break it down. Animals that can break down cellulose generally have symbiotic bacteria in their intestine that can break down cellulose.

Junior D

ScienceNerd wrote: »

Nipples - Men have nipples as when we develop in the womb we are essentially sexless for a while, and the female body is used as a template of sorts, before hormones kick in and give us our manly bits. At this point the nipples have already been formed.

Yawning - I believe this is an attempt to get more oxygen into your body when it's tired to try and revitalise it. Somebody may correct me on this though.

Full use of brains - No sure what you mean here, the old "only using 10% of our brains" is a myth.

Cellulose - We can't digest cellulose because it is a very tough material with many cross links, making it difficult to break down. As a result our digestive system doesn't hate the power to break it down. Animals that can break down cellulose generally have symbiotic bacteria in their intestine that can break down cellulose.

Thanks very much. I heard that answer about the nipples before but just making sure. As for the yawning I've heard many different theories. Sorry, I thought the brain thing was true. As for cellulose digestion, is that not what the appendix is for? or meant to be for anyway?

GLaDOS

Junior D wrote: »

As for cellulose digestion, is that not what the appendix is for? or meant to be for anyway?

Originally, yes, that's exactly what it was for. However it has become a vestigial (ie useless) organ since, and does not house the required bacteria for digestion any more.

Anthony Walsh

ScienceNerd wrote: »

Originally, yes, that's exactly what it was for. However it has become a vestigial (ie useless) organ since, and does not house the required bacteria for digestion any more.

Hasn't it been proving to be somewhat useful in the last few years.

http://scienceray.com/biology/human-biology/is-appendix-a-useless-organ/

Junior D

Why has it become useless though? Would its role not come in very handy? I thought these type of things only happen if there is no need for the organ?

GLaDOS

Anthony Walsh wrote: »

Hasn't it been proving to be somewhat useful in the last few years.

http://scienceray.com/biology/human-biology/is-appendix-a-useless-organ/

That's true, it's not quite useless, but it's primary function is defunct.

Junior D wrote: »

Why has it become useless though? Would its role not come in very handy? I thought these type of things only happen if there is no need for the organ?

I'm not completely sure myself, just the way evolution proceeded, hopefully someone else can answer it.

IrishKnight

Re cellulose digestion.

This is not my area of biology so I may be wrong in what I am about to say, but perhaps someone more enlightened can correct me if I am wrong.

As I understand stand it, cellulose is a rather poor when it comes to the energy that an animal gains from it. Basically, this means it is not an efficient food stuff. Rabbits, have huge appendix, which you rightly pointed out is need for cellulose digestion. However, when the grass has passed though their body once and pop out the other end, they eat their droppings, to get even more out of it.

Cows do something similar. They eat it, sallow it, bring it back up, eat it some more, sallow it and so on until it passes through their four stomachs.

Now, why can't humans do it? It comes down to our evolution and without going into great details, as we become more evolved and our brains started to grow, we needed more energy, we become more hungry! So, we started to eat other, energy rich foods, such as meat. We have evolved to eat high energy foods such as meats to such an extend that our body uses less energy eating meat than it would do with cellulose. Indeed, one of the reason we cook meat is to make it easier to digest!

As a side note, in humans, the appendix is what is known as a vestigial structure. All that means is that it is an overhang from our past when we did need it, but it has lost all or most of it's original function.

EDIT: Appears that when I was writing this the discussion was still going on, I hope that my reply explains why it became a vestigial structure.

gentillabdulla

Junior D wrote: »

I have a couple of questions here:

Why do men have nipples?

I thought it was because everyone was born female. Meaning that until they get either an x or y chromosome from your father then you are female.

And the nipples are a by-product of being a female.

http://www.scientificamerican.com/article.cfm?id=why-do-men-have-nipples

Money quote right here....

So, why do men have nipples? Because females do.

Another more relevant quote...

The uncoupling of male and female traits occurs if there is selection for it: if the trait is important to the reproductive success of both males and females but the best or "optimal" trait is different for a male and a female. We would not expect such an uncoupling if the attribute is important in both sexes and the "optimal" value is similar in both sexes, nor would we expect uncoupling to evolve if the attribute is important to one sex but unimportant in the other. The latter is the case for nipples.

I don't know much about this subject so please correct me if I am wrong.

IrishKnight

gentillabdulla wrote: »

I thought it was because everyone was born female. Meaning that until they get either an x or y chromosome from your father then you are female.

And the nipples are a by-product of being a female.

I wouldn't say it like that. We have to remember that you are when the egg fusses with a sperm, it is at that point the sex of the offspring is determined. It is just a matter of timing. The genes which make a male a male aren't turned on for a while so the default is female...

gentillabdulla

IrishKnight wrote: »

I wouldn't say it like that. We have to remember that you are when the egg fusses with a sperm, it is at that point the sex of the offspring is determined. It is just a matter of timing. The genes which make a male a male aren't turned on for a while so the default is female...

But your gender is still technically determined when you get the sperm from your father.

(By technically I mean it has been decided but hasn't been initiated.)

So there is a lag.

IrishKnight

gentillabdulla wrote: »

But your gender is still technically determined when you get the sperm from your father.

(By technically I mean it has been decided but hasn't been initiated.)

So there is a lag.

This is very true. The way I read what you wrote was that you appeared to be saying that you are growing away and a sperm comes along and determines what sex you are. Simple misunderstanding on my part.

Brendog

ScienceNerd wrote: »

Yawning - I believe this is an attempt to get more oxygen into your body when it's tired to try and revitalise it. Somebody may correct me on this though.

People yawn to remove excess CO2 that has built up within the body. When people strech it allows CO2 to pass round the body more easily which is why we usually have a massive strech/yawn when we wake up.

fontanalis

IrishKnight wrote: »

This is very true. The way I read what you wrote was that you appeared to be saying that you are growing away and a sperm comes along and determines what sex you are. Simple misunderstanding on my part.

I think it takes a while for the chromosome from the sperm to kick in, so the nipples are like a "default setting".

Rubecula

The main reason that the appendix has become defunct is apparently due to the way we have evolved with our diet. It is surmised that once our ancestors were primarily if not totally herbivores. The developing of carnivorous tendancies meant we obtained most of our protein from meat and hence had no need to eat vast quantities of vegetation. So the appendix had less and less use as we evolved.

Also there is the fact of cooking food which helps to break down strong structures, although I think this only started long after the appendix had started to become more vestigial anyway.

Capt'n Midnight

The Gelada Baboons of Ethiopia can eat grass. Would be interesting to know that adaptations they have and if we could borrow them.


Generally if the is no selective pressure against something then there is no harm in keeping it. Genetic drift will cause changes in stuff we don't need. We've lost about half the genes for smell since we developed colour vision and used it to detect ripe fruit.



Stuff that gets you killed will be lost in a few generations, which is why most African Elephants are now tuskless.

Stuff that is vital will be virtually unchanged after billions of years.



And yes we do make full use of our brains, because it's such a burden having to find food for it all the time, that it must have been of some use to our ancestors.

[edit]then again there is a bit of redundancy in the brain but it's not 90 %