sexual dimorphism

LightHorseman · #51 3rd July 2009, 12:39 AM

Originally Posted by ke1985

the male preying mantis doesn't think so

Try to remember that evolutionary benefit is not necesarily the same as benefit to individuals. Male preying mantis case in point.

corvus_corax · #52 3rd July 2009, 12:43 AM

Originally Posted by LightHorseman

Try to remember that evolutionary benefit is not necesarily the same as benefit to individuals. Male preying mantis case in point.

The advantages of sexual cannibalism are fascinating.

ke1985 · #53 3rd July 2009, 01:28 AM

then perhaps all female species should do this

hah jk

LightHorseman · #54 3rd July 2009, 02:30 AM

Originally Posted by ke1985

then perhaps all female species should do this hah jk

Once again, just because it works for one species does not mean it will be advantageous to all species.

Cave fish are benefited by NOT having eyes, but this is not a beneficial trait in all species.

iremouth · #55 3rd July 2009, 03:15 AM

Evolution is 99% common sense,(now that someone has shown us the way) it may not always seem to make sense but when you analyse it, it does, the bottom line is, what works wins, walk down the street and you will see people of every shape, size and colour, why is that? one would think that we have been around long enough now to be all the same shape and size so why should there still be differences? go to a library and pick out a few books on the subject, you will be amazed because it will all make sense.

dewaddict84 · #56 5th July 2009, 08:51 PM

Ke,

So me and Washington's explanation on page one was pretty good for explaining sexual dimorphism, but you seem to be picking apart details when you need to be looking at the larger picture. Or just the next sentence. After all, pages one, two, and three are you picking apart the first sentence here:

Larger females btw, make sense in terms of the birth size of the offspring. Or number of eggs laid, say. It all depends on the environmental situation.

When you really needed to take in the last sentence. It really does depend on the environmental situation. For some species, larger females will make sense. For others, the males has reasons for being larger. I'd say there are very very few general rules that apply for species for all time. And even for those rules, there are exceptions.

Also,

Cave fish are benefited by NOT having eyes

No. Well, only marginally due to efficiencies perhaps... But cave fish do not benefit from not having eyes, it's that they do not benefited from having eyes. So any vision-less offspring are not hindered compared to those with vision. ie, they have no reason to keep eyes. The difference is only slight and the outcome is the same, but I don't want people getting the wrong idea.

Bombila · #57 5th July 2009, 09:05 PM

Originally Posted by dewaddict84

Ke,
...
Also,

No. Well, only marginally due to efficiencies perhaps... But cave fish do not benefit from not having eyes, it's that they do not benefited from having eyes. So any vision-less offspring are not hindered compared to those with vision. ie, they have no reason to keep eyes. The difference is only slight and the outcome is the same, but I don't want people getting the wrong idea.

Very important point.

Evolution does not have a goal, does not purposely 'streamline' species, does not 'get rid of' unnecessary features. It is just that if a feature is not hindering or helping an animal (or a plant) in its ability to have healthy offspring who also survive to have healthy offspring (and ad infinitem), then whether the offspring are born with or without the feature makes no difference.

LightHorseman · #58 5th July 2009, 09:18 PM

No. Well, only marginally due to efficiencies perhaps... But cave fish do not benefit from not having eyes, it's that they do not benefited from having eyes. So any vision-less offspring are not hindered compared to those with vision. ie, they have no reason to keep eyes. The difference is only slight and the outcome is the same, but I don't want people getting the wrong idea.

Of course they benefit from not having eyes. Do you have any concept of how expensive eyes are in terms of resources and maintenance? If eyes confer no benefit, than an animal without eyes will outcompete an animal with eyes every time... it needs that much less nutrients to survive, and needs expend that much less energy on maintaining its eye structures. In a depleted resource environment... like, I dunno... a CAVE maybe, this is a real advantage.

redwards · #59 5th July 2009, 10:08 PM

ke1985, if you're genuinely interested in these subjects, you would be fascinated by The Selfish Gene, which explains in stupendous detail why and how evolution proceeds, and how certain aspects of evolution which we take for granted have come about (such as why there are two sexes at all -- which isn't true of all species). I understand that it can be difficult for a person of faith to pick up a book by Richard Dawkins, but you might note that he wrote this book decades before he became famous for atheism.

Bombila · #60 5th July 2009, 11:03 PM

Originally Posted by LightHorseman

Of course they benefit from not having eyes. Do you have any concept of how expensive eyes are in terms of resources and maintenance? If eyes confer no benefit, than an animal without eyes will outcompete an animal with eyes every time... it needs that much less nutrients to survive, and needs expend that much less energy on maintaining its eye structures. In a depleted resource environment... like, I dunno... a CAVE maybe, this is a real advantage.

Whoa, Lighthorseman! That's one of three main theories regarding loss of eyes in cave animals. Note the third.

The mystery behind cave animals is why are eye size and pigmentation reduced? There are three main theories; the first is that eye size and pigment loss is advantageous in cave animals because of energy conservation. The second is that eye and pigment loss is advantageous in cave animals because the genetic changes that cause eye and pigment loss also cause adaptive changes that allow the animals to be better suited to life in the cave. The final theory is that neutral mutation causes regression of the eye development and pigmentation pathways because there is no selective advantage to maintaining these systems in the dark environment.

Free Association: Paper trail: cavefish genetics