TransformerRobot Posted June 30, 2012 Posted June 30, 2012 Why do women have 2 ovaries? They only need one in the womb, and it won't give them twins unless it divides, right?
TransformerRobot Posted July 1, 2012 Author Posted July 1, 2012 Because the body develops symmetrically. Well that makes sense, but why is the heart more towards the left nipple in the human body? Kind of asymmetrical if you ask me.
ecoli Posted July 1, 2012 Posted July 1, 2012 Well that makes sense, but why is the heart more towards the left nipple in the human body? Kind of asymmetrical if you ask me. I don't think it is. The left wall is thicker because that's where the major pump mechanism is and the whole thing is slightly slanted, hence why it sounds a bit louder on the left side.
Moontanman Posted July 1, 2012 Posted July 1, 2012 Why do women have 2 ovaries? They only need one in the womb, and it won't give them twins unless it divides, right? I'm curious, do you know what a woman's ovaries are and how they work? There being two has nothing to do with twins or the likelihood of twins... 1
TransformerRobot Posted July 1, 2012 Author Posted July 1, 2012 I'm curious, do you know what a woman's ovaries are and how they work? There being two has nothing to do with twins or the likelihood of twins... Yes, but my previous knowledge of how more than one child ends up in the womb escapes me.
Moontanman Posted July 1, 2012 Posted July 1, 2012 (edited) Yes, but my previous knowledge of how more than one child ends up in the womb escapes me. Identical twins, one egg/embryo in the uterus splits into two embryos after fertilization. Fraternal twins, two eggs end up in the uterus and are fertilized separately. The two eggs can come from different ovaries or the same ovary... Fraternal twins can have different fathers... Edited July 1, 2012 by Moontanman
TransformerRobot Posted July 1, 2012 Author Posted July 1, 2012 Identical twins, one egg/embryo in the uterus splits into two embryos after fertilization. Fraternal twins, two eggs end up in the uterus and are fertilized separately. The two eggs can come from different ovaries or the same ovary... Fraternal twins can have different fathers... You mean the father would have to impregnate 2 different women to get fraternal twins? Or it would be just one mother, with both eggs reaching the uterus?
Moontanman Posted July 1, 2012 Posted July 1, 2012 You mean the father would have to impregnate 2 different women to get fraternal twins? Or it would be just one mother, with both eggs reaching the uterus? One mother, two eggs, two fathers... but that would be quite rare, I would have to assume that sexual intercourse would have to be reasonably close together involving two men, most fraternal twins have one father and one mother. I'm not sure if there is such a thing as fraternal triplets but I can't see why it couldn't happen. 1
Delta1212 Posted July 1, 2012 Posted July 1, 2012 (edited) It's also a case of redundancy. You only need one ovary to reproduce, but what happens if it gets damaged? Then you're screwed (but not getting pregnant). Now you might say that you could also use a redundant heart as well, but it would be much harder to introduce an extra heart into the circulatory system without mucking it up, especially since the damage done to a heart would probably be fatally destructive to your vascular system even if you had a spare to keep beating. Edited July 1, 2012 by Delta1212
Appolinaria Posted July 1, 2012 Posted July 1, 2012 Fraternal twins can have different fathers... Jiminy mother effing cricket. I guess you learn something new everyday.
Moontanman Posted July 1, 2012 Posted July 1, 2012 Jiminy mother effing cricket. I guess you learn something new everyday. There are many examples of this, many times it goes undetected but a woman giving birth to two children and one of them is obviously of African decent and the other blond haired blue eyed and very light complected is hard to ignore. DNA has also confirmed this but i wonder if fraternal triplets have ever had three different fathers? http://en.wikipedia.org/wiki/Superfecundation
jimmydasaint Posted July 1, 2012 Posted July 1, 2012 Identical twins, one egg/embryo in the uterus splits into two embryos after fertilization. Fraternal twins, two eggs end up in the uterus and are fertilized separately. The two eggs can come from different ovaries or the same ovary... Fraternal twins can have different fathers... I always thought that identical twins are exactly as you described (and have to be the same gender because this is an example of natural cloning). However, IIRC, fraternal, or non-identical, twins are caused by two different sperms from the same father fertilising two different ova from the mother. Due to the 'gene shuffling' that occurs in the process of meiosis before sperm or eggs are made, the fraternal twins are likely to be different in both genes and looks. The example you gave of superfecundation where a mother can give rise to twins from two different fathers is, IMO, a much rarer event. Twins Meiosis Facts Meiosis Text 1
zapatos Posted July 1, 2012 Posted July 1, 2012 There are many examples of this, many times it goes undetected but a woman giving birth to two children and one of them is obviously of African decent and the other blond haired blue eyed and very light complected is hard to ignore. DNA has also confirmed this but i wonder if fraternal triplets have ever had three different fathers? http://en.wikipedia.org/wiki/Superfecundation I don't know how accurate this is but it is all I could find on the subject of triplets with three fathers. There is, of course, nothing limiting heteropaternity to two children. Triplets, quadruplets, or even nontuplets could all possess different fathers given enough ova and a sufficient variety of male genetic material. But considering the almost inconceivable odds against such a series of events, it is little surprise that no instances of heteropaternal triplets or higher have ever been reported. http://www.damninteresting.com/half-brothers-in-the-womb/ Identical twins, one egg/embryo in the uterus splits into two embryos after fertilization. Fraternal twins, two eggs end up in the uterus and are fertilized separately. The two eggs can come from different ovaries or the same ovary... Fraternal twins can have different fathers... Huh. Now that you've got me looking, it seems as if there is another category of twin. Half identical twins occur when the egg splits prior to fertilization. A Third Kind of Twins: Polar-Body or Half Identical Twins In simplest terms, if the egg splits and is fertilized by two different sperm, the embryos share the mother's genes from the ovum, but the genetic material coming from the sperm will be different because two sperm were involved. This makes them polar-body or half identical. According to the NOMOTC, "They share some features of identical twins and some features of fraternal twins." There is debate among experts as to whether or not polar-body twins constitute a completely new category of twins. For now, however, they remain a subgroup of identical twins. 2
magna_nz Posted August 7, 2012 Posted August 7, 2012 As said as above, a case of redundancy. Same as asking "why do we have kidneys, instead of 1 when all we need is 1"? It's like a failsafe.
Derin Posted September 11, 2012 Posted September 11, 2012 Birds generally have one working ovary, presumably to save on weight. Their body layout can accommodate two, it's just that one withers away. We have two ovaries, two kidneys, two lungs, etc., because we are bilaterally symmetrical. It's "easier", if you like, for a body to develop basically symmetrically on either side, with some modifications to organs that need to be asymmetrical (such as the larger left side of the heart, due to the pumping requirements of each side, the appendix, and the birds having only one functioning ovary.) This works really well because, as Delta and magna explained, it provides redundancy, so the organism has a backup in case of injury, infection or developmental defect.
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