The evolution of complex characters—Two Themes:
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Transcript of The evolution of complex characters—Two Themes:
The evolution of complex characters—Two Themes:
1)Complex characters can evolve gradually via intermediate forms(if those forms have adaptive value)
2) Cooption of pre-existing genes for new purposes
We will focus first on #1. “What good is half an eye?”
http://www.youtube.com/watch?v=J3sgoy22Ij4
Even single-celled organisms can sense lightEuglena respond to light by moving flagellum
Does this lowly form of vision have adaptive value?What could it be?
These are representatives of different eye types currently found in nature. They may be similar to the intermediate stages long ago passed on the way to our eye.It is unlikely to evolve a complex eye “from nothing”—i.e., Boeing 747 mutations.But incremental improvements from simple photoreceptors to more complex eyes
are very likely.
Fig. 25-24
(a) Patch of pigmented cells-limpet
Opticnerve Pigmented
layer (retina)
Pigmented cells(photoreceptors)
Fluid-filled cavity
Epithelium
Epithelium
(c) Pinhole camera-type eye-Nautilus
Optic nerve
Cornea
Retina
Lens
(e) Complex camera-type eye-squid
(d) Eye with simple lens-marine snail
Optic nerve
CorneaCellularmass(lens)
(b) Eyecup-slit-shell mollusc
Pigmentedcells
Nerve fibers Nerve fibers
• http://richarddawkins.net/videos/527044-bang-goes-the-theory-richard-dawkins-on-eye-evolution
http://www.pbs.org/wgbh/nova/evolution/intelligent-design-trial.
htmlWatch Behe at 1:06
• http://cosmiclog.msnbc.msn.com/_news/2011/04/08/6433919-intelligent-design-in-tenn-schools