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Life History Parameter: Sex ratio/Age of First Reproduction

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Life History Parameter: Sex ratio/Age of First Reproduction

Postby sole_05 » Mon Jun 06, 2005 4:38 pm

Some interesting issues that needs some input to clarify some of these evolutionary changes in human sex ratio and age of first reproduction. Here we go!

1. There is common concept that males in some human professions (e.g. deep sea divers, footballers) are more likely to father daughters than sons. Just wondering if there is an evolutionary explanation for why particular males may be more likely to have daughters? Can you think of a mechanism explanation of how this might happen?


2. Even for the earliest maturing species of animals and plants there is always a development phase before individuals are fully mature and able to reproduce. But why is it so rare for species to be born with fully reproductive organs ready to go?


3. Back to humans. Another common concept is that the age of maturity in humans has been declining over recent centuries. ie. humans are capable of reproducing at an earlier age now than they could three or four hundreds years ago. Any explanation on this, and what role of evolution in this change?

Would appreciate any thoughtful comments.
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Postby James » Mon Jun 06, 2005 4:58 pm

Wouldn't really be benficial to be able to reproduce immediately. The population would surely become overcrowded; the body wouldn't be prepared to give birth; the likelyhood of survival for offspring is low enough without having to mate and give birth etc etc

Physical evolution over a few hunded years is not the answer, it's more likely a social and behavioural change.
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Postby MrMistery » Mon Jun 06, 2005 6:27 pm

1. This is wrong. The probability is 50-50, the profession of the father has nothing to do with it. Think of it like this: a football player has a boy, he teaches his son footbal, happy family, end of story. He has a daughter, he will complain to everybody that he has a daughter. So, it is more likely that you hear about him having a daughter than a son--> that popular belief

2. This differs for r and k organisms. R organisms usually are closer to that situation than k organisms.

3. Like it was said, it is a matter of behaiviour. In USA, one out of 10 children has sex before the age of 13(i was stunned when i heard this!). Though I, as a 13 year-old, could have sex at this age 300 years ago, i was not permitted to. Since now we live in a more liberal society, girls, watch out! :wink:
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Postby Poison » Mon Jun 06, 2005 6:33 pm

sex is an instinct. You can not stop it... ;)
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Postby MrMistery » Mon Jun 06, 2005 6:40 pm

Yeah, but sometimes we need to control our instincts. Fortunately, only sometimes :D
By the way i am not 13. Am i am 16 and a half :D
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Postby mith » Mon Jun 06, 2005 7:56 pm

1.Football players might get hit in the nuts more than people in other professions. I dunno how that might affect sperm count though :wink:

2.Probably requires too much energy. The parent would need to contribute extra energy to support the child and allow it to mature sexually, and the child would expend extra energy to keep the sexual organs functional. I'd think that the first priority is not sex, but survival.

3.Not sure about this. Wasn't Juliet 13 and Romeo 15?
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Postby MrMistery » Mon Jun 06, 2005 8:59 pm

Hello... That wasn't for real!! Shakespeare imagined it :D Anyway, it was simply an opinion
PS: you are probably right on the second one
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Postby Poison » Tue Jun 07, 2005 6:16 pm

At the age of 13 you can have sexual desire. Especially if u are a girl. And you know, the age of teenage can change.
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Postby MrMistery » Wed Jun 08, 2005 8:17 pm

I saw a boy on a talk-show who began his sexual life at the age of 9. That is twisted
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Postby Poison » Thu Jun 09, 2005 6:05 pm

9? with whom? I don't think it is normal, Actually, I'm sure that it isn't normal. :)
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Postby MrMistery » Thu Jun 09, 2005 9:24 pm

With a 12 year-old girl who had done it before and taught him
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Postby har0bed1813 » Fri Jun 10, 2005 12:39 pm

that's really sick... Half my friends are stil virgins, and they are mostly 16-20!
and I think it's not just evolution, but mostly upbringing and culture.
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