Freethought & Rationalism Archive

thebeave · 12-31-2002, 09:03 AM

Quote:

Originally posted by semyaza
Apologies if this has been posted before (couldn't find it in the search)...

It seems that the human female reproductive system is rather strangely designed. The average human female is born with 1 to 2 million eggs. However, the vast majority of these eggs can never be fertilized.

The average female will release one egg per cycle, about thirteen a year. Assuming that her fertile period lasts fifty years, this makes for a total of 650 eggs over a lifetime. Let's be generous and round that up to a thousand. That's still about 0.1% of the total number of eggs that she is born with.

When humans design systems for tough terrains (such as interplanetary travel) it is not uncommon to use redundant backups. However, no engineer would ever design a system with a thousand backup units. That would be both pointless and wasteful.

Why, then, did the Creator design such a strange system? The vast majority of a woman's eggs will not, indeed cannot, be fertilized. In fact, the majority of these eggs will die before she even reaches puberty.

Millions of female eggs makes no sense in mammals. However, amongst fish it does make sense. Since a female fish has a limited ability to defend her young, it makes more sense for her to lay thousands of eggs, thus increasing the chances that some will survive to adulthood.

Is it possible that the human female's millions of eggs is a relic of the very distant past, and has nothing at all to do with design, intelligent or otherwise?

I don't think it was wise to put this information out in the open like this. The Catholic and Mormon fundies will interpret this "design" to mean that God intends for them to have even larger families than they previously believed!

Back on the topic, there is a pretty damn big span of time between modern day humans and our early fish ancestors. It would seem to me that this ancient carryover from our days as fish would have long disappeared for one reason or another. Wouldn't it?

Ab_Normal · 12-31-2002, 09:55 AM

Quote:

Originally posted by thebeave
Back on the topic, there is a pretty damn big span of time between modern day humans and our early fish ancestors. It would seem to me that this ancient carryover from our days as fish would have long disappeared for one reason or another. Wouldn't it?

If I understand natural selection correctly, there's no selective pressure against having a bajillion eggs, since it doesn't keep a female from reproducing. All you educated folks, please straighten me if I'm incorrect. Thanks.

semyaza · 12-31-2002, 11:08 AM

Quote:

Originally posted by Ab_Normal
If I understand natural selection correctly, there's no selective pressure against having a bajillion eggs, since it doesn't keep a female from reproducing. All you educated folks, please straighten me if I'm incorrect. Thanks.

That is my understanding. Having a thousand times more eggs than necessary doesn't buy you anything - but it also doesn't cause much of a drain on resources. Therefore, there is no selective advantage to having fewer eggs, and hence the trait is not 'deselected'.

It's pretty much the same reason why we still have appendixes (appendices?) and body hair.

thebeave · 12-31-2002, 11:52 AM

Quote:

Originally posted by semyaza
That is my understanding. Having a thousand times more eggs than necessary doesn't buy you anything - but it also doesn't cause much of a drain on resources. Therefore, there is no selective advantage to having fewer eggs, and hence the trait is not 'deselected'.

It's pretty much the same reason why we still have appendixes (appendices?) and body hair.

Body hair and appendices I can see. That was in the not-too-distant past. But fish? We're talking over a billion years ago at least, are we not? Seems like have 1.21 jigaeggs is putting a more than necessary demand on the reproductive system. I don't know... I guess I can't come up with a good reason right now why it COULDN'T be a fish leftover. It just seems like something would have phased it out long ago.

Valentine Pontifex · 12-31-2002, 12:17 PM

Quote:

Originally posted by MrDarwin
Just goes to show what we already knew, God likes boys better than girls

Girls get the last laugh though -- they live longer.

pz · 12-31-2002, 01:01 PM

Quote:

Originally posted by thebeave
Body hair and appendices I can see. That was in the not-too-distant past. But fish? We're talking over a billion years ago at least, are we not? Seems like have 1.21 jigaeggs is putting a more than necessary demand on the reproductive system. I don't know... I guess I can't come up with a good reason right now why it COULDN'T be a fish leftover. It just seems like something would have phased it out long ago.

Just to correct a few things...

Human females don't have billions of eggs. They start out with many, but during puberty, most of the oocytes are resorbed and 'only' about 40,000 are left. Roughly 400 will be used during the woman's reproductive lifetime, so it's about a 100-fold excess. This actually may not be as great an excess as it sounds -- apparently, there is a bit of sorting going on in the ovaries, and the eggs are selected for ovulation in roughly the order of their quality. So 100 times as many as are necessary are produced, but that just means there is an opportunity to throw out the bad eggs.

One reason mammalian females do this rigamarole of initiating the whole gamete package before puberty is to reduce the number of cell cycles that the oocyte goes through. Each cell division is an opportunity for error, so by minimizing cell cycles, the female reduces the number of chances for mutations to creep in. Males maintain a continuously cycling population of stem cells to generate lots of gametes, but this unfortunately means that they also contribute 4-8 times as many new mutations to their progeny as do females.

This is not a holdover from fish. Female fish tend to produce eggs in the same way that human males produce sperm -- profligately.

The last common ancestor of modern fish and mammals lived about 400 million years ago, not a billion.

lpetrich · 12-31-2002, 01:05 PM

Fish ancestry dates back to ~400 million years ago: the Silurian and Devonian geological periods when early fish proliferated and diversified.

As to fishlike features being preserved all that time, several of them continue to be preserved in embryos, such as gill bars and gill pouches -- though not fully-functional gills. These have various fates, some being resorbed, the frontmost gill bars becoming jawbones, etc.

Yes, both upper and lower jawbones originate from the frontmost gill bars, as can be seen from embryos from all across the jawed vertebrates.

GunnerJ · 01-01-2003, 03:24 PM

Quote:

Originally posted by Valentine Pontifex
Girls get the last laugh though -- they live longer.

"The flame that burns twice as bright burns half as long."

Seems a fair tradeoff.

Demigawd · 01-01-2003, 03:50 PM

Quote:

Originally posted by Rimstalker
"The flame that burns twice as bright burns half as long."

Seems a fair tradeoff.

Male bovine feces! Women get multiple orgasms. Couple that (no pun intended) with lesbianism, and you've got the recipe for Heaven on Earth.

Boro Nut · 01-02-2003, 08:57 AM

Quote:

It seems that the human female reproductive system is rather strangely designed. The average human female is born with 1 to 2 million eggs. However, the vast majority of these eggs can never be fertilized.

Well of course they can't. How on earth could you expect a poor bloke to bring home the bacon for 1 to 2 million kids? He would need 103,664.8 jobs by my calculation, and statistically you would have no chance of remembering which ones didn't like bacon.

Also, the poor woman would be in a constant state of labour, leaving her no time to sit around on her fat arse smoking and talking to her mates.

Boro Nut

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12-31-2002, 01:05 PM	#17
lpetrich Contributor Join Date: Jul 2000 Location: Lebanon, OR, USA Posts: 16,829	Fish ancestry dates back to ~400 million years ago: the Silurian and Devonian geological periods when early fish proliferated and diversified. As to fishlike features being preserved all that time, several of them continue to be preserved in embryos, such as gill bars and gill pouches -- though not fully-functional gills. These have various fates, some being resorbed, the frontmost gill bars becoming jawbones, etc. Yes, both upper and lower jawbones originate from the frontmost gill bars, as can be seen from embryos from all across the jawed vertebrates.

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