sexual dimorphism

It demonstrably makes them more competetive. Theory three is inadequate to address the issue.

Which is why I don't like the phrase "Survival of the fittest".
I prefer "Survival of the fit enough".

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Good point.

You know the story of the two guys who's car broke down in lion country?

They decided to make a run for it, but before opening the door, the first guy said "wait a sec, let me put on my super new Nike air adidas Jordan Reeboks first"

The second guy snorted "what, you think thats going to make you otrun a lion?"

The first guy, finsihed tying his laces looked up and said "Outrun a lion? Mate, all i have to do is outrun YOU!"

Pretty good summary of the evolutionary selection process.

I might have missed many intelligent, well thought-out answers, but I can't be bothered to read I don't know how many pages right now. So apologies if I repeat what someone else said.

I also don't know a lot about sexual dimorphism in particular, so I can't really say much more than generalities. (I probably could a year from now, but it's not a year from now and I haven't taken the module on breeding systems yet )

Originally Posted by ke1985

How do evolutionists explain sexual dimorphism?

That depends on the particular example you have in mind. Sexual dimorphism comes in many shapes, and you can't explain all of them with a single adaptive advantage. I wouldn't be entirely surprised if some cases even turned out to be a result of simple inertia (i.e. dimorphism was useful for a creature's ancestors and it just wasn't disadvantageous enough to disappear from the descendants).

Couple examples.

It's often about investment.

(1) In elephant seals, I can think of two things that can drive sexual dimorphism: first, females rear their pups alone, second, suitable beaches where they can give birth and mate are limited. So males have a golden opportunity: seize the breeding area and force all the females there to have your pups, and your genes invade the next generation. Now, the only problem is that all males want to do this... no surprise at all that the big ones get the most matings.

(1a) Most female birds can't be forced to mate (it's a bit difficult to rape someone without a penis) - but their large eggs still take a lot to produce, which means they don't want to waste those resources on any random guy. Hence choosy females, and males who wave their pretty feathers around, sing the most complex songs they can or try to secure good territories.

(2) In some bush crickets, males are choosy and females chase them. Male crickets often give large edible gifts to females (although the nutritional value of these gifts is sometimes suspect... not going off on that tangent now ). The package is attached to the bag of sperm the male transfers while mating, and the longer she nibbles on the gift, the longer he has to ensure she is fertilised by him. Presumably, the more gifts she gets, the better she can provision her offspring. Now, these packages can make up almost half the male's body mass, so he won't give them away to any girl that crosses his path. This is pretty much the opposite of the "conventional" sex roles, where females pay most of the price and males try to get as many of them as possible. Interestingly, if you give the crickets extra food, sex roles are reversed...

(3) Then there are true weirdos like anglerfish. In their case, there's little point in chasing many skirts. When you are a predator in the deep sea where prey is rare, your species will also be rare and you'll have difficulty finding even one mate. Anglerfish solve the problem by never letting go of a mate they do find. You may have heard of male anglerfish that fuse with their mate and degenerate into a pair of testicles in a bag...

Originally Posted by ke1985

What is the difference of roles between the male and female blue whale?

The female has to bear and nurse big, hungry baby whales

Originally Posted by ke1985

Females are generally 10-20 feet longer and heavier than males.

I don't know how true this is of blue whales, but AFAIK big whales that feed in cold waters and breed at lower latitudes don't eat a lot in their breeding areas. Females need to have massive fat stores to be able to complete a migration and rear a calf without replenishing those supplies. The bigger you are, the more fat you can store and the less energy you need per unit body mass --> the more you can spare for the young one.

I seem to recall that the bigger females trend applies to other baleen whales as well.

Originally Posted by ke1985

Hyenas are larger than males and have around the same birth size as lions but lionesses are smaller than the males.

I don't know why female hyenas are larger, but male lions better be big and strong (and not alone) if they want to rear any cubs at all. Now don't ask me why they have the social system they have, because I haven't a clue

King cobra males are bigger but female anacondas are bigger.

Is there a behavioural difference between these snakes? Do king cobras fight for females and anacondas not? Or are there different demands on the females? Either of these things, or a combination, could explain the difference. One thing that just popped into my mind is that these animals have very different hunting methods. For an anaconda, size and strength can ensure bigger prey/more hunting success (i.e. more food for making eggs), but how much does it matter for a venomous snake?

This theory does not apply like you say it does.

Yes, the real world is complicated. Which is what makes it so much fun to discover

I am just curious on why the size of sex fluctuates so much in the animal kingdom...although not in the primate group.

Actually, sexual dimorphism does vary in primates. I don't know if any primate has bigger or more ornamented females than males, but in addition to species where males are much larger (gorillas, for example) and/or have ornaments (mandrills, proboscis monkeys), there are also species where the two sexes are similar in size and appearance (cotton-top tamarins, for example).

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"There is much we do not understand about the history of life, and the same will be true of our grandchildren. But, then, if we knew all there was to know, scientific interest would cease. Textbooks may portray science as a codification of facts, but it is really a disciplined way of asking about the unknown." - A.H. Knoll, Life on a Young Planet

"Come on, put your bloody thinking caps on!" - Dr Tony Prave, geology lecture

Just wanted to bump this, as I think it's a shame that Naraoia's fine post is the last thing posted (i.e. ignored).

I get the feeling the OPer simply wanted everyone to respond with "I don't know", so (s)he could claim victory. Creationists often like to pose one-liner questions, for no other purpose than to stump people. These questions often require alot of knowledge, research and patience to respond to adequately, and the answers demand a certain understanding of the recipient. The worst thing you can do to them is to provide a high quality/fulfilling answer, or simply show them that you're interested in an open-minded debate.

Peter

Ow

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"There is much we do not understand about the history of life, and the same will be true of our grandchildren. But, then, if we knew all there was to know, scientific interest would cease. Textbooks may portray science as a codification of facts, but it is really a disciplined way of asking about the unknown." - A.H. Knoll, Life on a Young Planet

"Come on, put your bloody thinking caps on!" - Dr Tony Prave, geology lecture