Register | Sign In


Understanding through Discussion


EvC Forum active members: 65 (9162 total)
5 online now:
Newest Member: popoi
Post Volume: Total: 915,821 Year: 3,078/9,624 Month: 923/1,588 Week: 106/223 Day: 4/13 Hour: 0/2


Thread  Details

Email This Thread
Newer Topic | Older Topic
  
Author Topic:   Can sense organs like the eye really evolve?
caffeine
Member (Idle past 1025 days)
Posts: 1800
From: Prague, Czech Republic
Joined: 10-22-2008


(3)
Message 6 of 242 (636400)
10-06-2011 9:37 AM
Reply to: Message 1 by ANI
10-06-2011 8:39 AM


Jellyfish
For a practical example of an animal with light-sensitive organs but without a brain to respond to them, consider jellyfish. Some jellyfish have light-sensitive organs, but none of them have brains. Jellyfish can't see an image, since they have no image processing hardware, as you say. Instead, the light sensitive organs simply connect to nerves, which connect to muscles, to bring about automatic reactions like swimming towards and away from light.
However, once nerves have clumped together to form a brain, with the capacity for evolving image-processing capabilities, the light-sensitive organs are already there, ready to be co-opted for just such a purpose.
Edited by caffeine, : Because 'automative' isn't a word.

This message is a reply to:
 Message 1 by ANI, posted 10-06-2011 8:39 AM ANI has not replied

  
caffeine
Member (Idle past 1025 days)
Posts: 1800
From: Prague, Czech Republic
Joined: 10-22-2008


(1)
Message 54 of 242 (636705)
10-10-2011 6:51 AM
Reply to: Message 41 by Taz
10-07-2011 3:41 PM


Taz writes:
Actually, no. All features are transitional features. Or one could argue that there is no such thing as transitional features because the term itself refers to an "in-between" feature, and there is no such thing.
The very term was conjured up by creationists as a strawman trying to diverge attention away from real science. They want people to believe scientists believe there were once upon a time half an eye, half a leg, etc.
The earliest use of "transitional form" and "transitional variety" that I can find is from a book not renowned for its creationist bent - 'The Origin of Species', by one Charles Darwin:
quote:
As natural selection acts solely by the preservation of profitable modifications, each new form will tend in a fully-stocked country to take the place of, and finally to exterminate, its own less improved parent or other less-favoured forms with which it comes into competition. Thus extinction and natural selection will, as we have seen, go hand in hand. Hence, if we look at each species as descended from some other unknown form, both the parent and all the transitional varieties will generally have been exterminated by the very process of formation and perfection of the new form.
But, as by this theory innumerable transitional forms must have existed, why do we not find them embedded in countless numbers in the crust of the earth?
  —Charles Darwin
...and so on. I've been unable to locate the origin of the specific term 'transitional feature', but it's used commonly in scientific publications.
Not all features are transitional. A transitional feature would be one that is morphologically intermediate between primitive and derived members of a group. Archaeopteryx's tail could be said to be a transitional feature, since it combines traits that are primitive to Theropoda (long chevrons) and derived traits of birds (feathers).
The peacock's tail, on the other hand, is not a transitional feature. There's no more derived tail we can point to, for which the peacock's tail would stand as a good intermediate between it and primitive birds' tails.
Edited by caffeine, : No reason given.
Edited by caffeine, : To add the quote from Taz

This message is a reply to:
 Message 41 by Taz, posted 10-07-2011 3:41 PM Taz has not replied

Replies to this message:
 Message 55 by Parasomnium, posted 10-10-2011 8:20 AM caffeine has seen this message but not replied

  
caffeine
Member (Idle past 1025 days)
Posts: 1800
From: Prague, Czech Republic
Joined: 10-22-2008


Message 196 of 242 (639112)
10-28-2011 5:41 AM
Reply to: Message 190 by Robert Byers
10-28-2011 4:56 AM


There is not diversity relevant to the diversity in all other organs or body shapes of nature.
Where is this much greater diversity in other organs? When I turn to the section on hearts in my vertebrate anatomy book, I can look up mammal hearts and read about their basic structure. And they all have the same basic structure - they've all got the same fully divided atria and ventricles, with the same basic pattern of veins and arteries coming in and out; whether they be whales or mice or monkeys or kangaroos - because they're all mammals. Sure, there are some differences between them, just as different mammals have eyes with or without colour vision; with varying densities of rods; with bigger or smaller apertures; with different orientations etc. depending on their lifestyles. But the same basic design since they all share a recent common ancestor.
Why would you expect different for eyes than for hearts?

This message is a reply to:
 Message 190 by Robert Byers, posted 10-28-2011 4:56 AM Robert Byers has not replied

  
caffeine
Member (Idle past 1025 days)
Posts: 1800
From: Prague, Czech Republic
Joined: 10-22-2008


Message 217 of 242 (639410)
10-31-2011 12:04 PM
Reply to: Message 216 by Taq
10-31-2011 11:27 AM


Actually, it was first drawn by Linnaeus, 100 years before "Origin of Species" was published. The tree is formed by shared characteristics, not evolutionists.
Well, not really. Linnaeus recognised hierarchies of characteristics, but he didn't draw any 'tree of life'. You can argue the idea is derived from concepts recognised by non-evolutionary biologists, but a branching tree is, nonetheless, an evolutionists' idea, drawn and conceived by evolutionists. This seems to be the earliest drawing, from French botanist Augustin Augier in 1801 (warning, full size image is big)

This message is a reply to:
 Message 216 by Taq, posted 10-31-2011 11:27 AM Taq has replied

Replies to this message:
 Message 218 by Taq, posted 11-01-2011 11:22 AM caffeine has not replied

  
Newer Topic | Older Topic
Jump to:


Copyright 2001-2023 by EvC Forum, All Rights Reserved

™ Version 4.2
Innovative software from Qwixotic © 2024