Transcript Anatomy

Homologous structures
• Homologous structures are those that appear similar in
related species
• Evolution predicts that certain organs, over a great deal of
time, may change their function as a lineage evolves
• Exaptation : The modification of use of an existing organ
for a different function in a direct evolutionary descendant.
• Do similar features merely propose the same designer?
– No, because in most cases the best option for a designer
would have been to completely redesign the organ from
scratch rather than modify an existing organ to do something
that it wasn’t originally ‘meant’ to do
– Also, we have intermediate stages for many of these
© Colin Frayn, 2008
www.frayn.net
Haeckel’s Embryos (1)
Stages
of
development
A copy (1892) of Ernst
Haeckel’s original embryo
sketches
Different
animals
© Colin Frayn, 2008
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Haeckel’s Embryos (2)
• Haeckel faked some aspects of his original
drawings
– They are nowadays accepted as fraud
• Some aspects were accurate and relevant
– ‘Recapitulation theory’
– Many aspects of ontogeny (embryo growth)
really do echo historical evolutionary stages
• Whales have hair and leg bones
• A structure resembling the tail of primates recedes to
form the human coccyx bone
• Swim bladder of fish develops first as a component of
the gut, according to its presumed evolution, and
then later detaches from the gut completely
© Colin Frayn, 2008
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Ontogeny recapitulates phylogeny
• The ‘subtitle’ of Haeckel’s
Recapitulation hypothesis
• This theory suggests that embryological
stages remind us of the evolutionary
history of an organism
• This is somewhat true, but is largely
discredited in the sense that Haeckel
intended it
© Colin Frayn, 2008
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Gill slits in embryos
• Do human embryos have ‘gill slits’
reminiscent of their evolutionary history?
• No, though they do have features
that resemble gill slits called
pharyngeal pouches
– In humans, these features have nothing
to do with breathing
– All vertebrate embryos have these
– In fish, these do develop into gills
– Common features are strong evidence
for common ancestry
© Colin Frayn, 2008
www.frayn.net
Vestigial organs
Vestigial organs are supposed ‘remnants’ of
evolutionary history that have not yet fully
disappeared
• Tiny leg bones in whales
• The human appendix
• Eye remnants in blind cave fish
These may have minor functions, but certainly not
the ‘obvious’ ones.
They are remnants of a more prominent organ
which has become redundant.
© Colin Frayn, 2008
www.frayn.net
The Eye
Is the eye too complicated to have evolved?
• The eye could easily have evolved in under a
million years
– Nilsson & Pelger (1994)
• Many different eye types exist in nature
– The eye has evolved many times
• Maybe from a very simple common ancestor organ
• Maybe totally independently
• The eye is evidence of poor design
– The retinal cells are ‘plugged in’ backwards!
– The contrary claims of Michael Denton and others are
not plausible
© Colin Frayn, 2008
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Eye Anatomy
Blind spot where
the optic nerve
crosses the retina
© Colin Frayn, 2008
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Inverted Retinal Cells
The photoreceptive cells in the retina of the human
eye are plugged in backwards
• This means that:
– Less light gets to the photo receptors
– We have a blind spot
– We are susceptible to many more blinding diseases
• Several creationists have tried to claim that this is a good
design after all
• These arguments are flawed
– An intelligent designer would have designed the eye differently
• Top-down design would avoid the problems that we see
– We have a jerry-rigged organ designed to solve problems that
need not even exist
© Colin Frayn, 2008
www.frayn.net
Darwin and Eye Evolution
• Did Darwin write “To suppose that the eye … could have been
formed by natural selection, seems, I freely confess, absurd in the
highest possible degree”?
• Yes, and he followed it with the words: “Yet reason tells me, that
if numerous gradations from a perfect and complex eye to one
very imperfect and simple, each grade being useful to its
possessor, can be shown to exist; if further, the eye does vary
ever so slightly, and the variations be inherited, which is certainly
the case; and if any variation or modification in the organ be ever
useful to an animal under changing conditions of life, then the
difficulty of believing that a perfect and complex eye could be
formed by natural selection, though insuperable by our
imagination, can hardly be considered real.”
• And then he quoted several pages of suggested evolutionary
models.
© Colin Frayn, 2008
www.frayn.net
Irreducible Complexity
• Structures that cannot work if any one of their
parts is not present
– There are many of these, but…
• Structures may have had alternate uses before
evolving to their current form
• Bacterial flagellum
– An ‘engine’ for bacteria
– A plausible evolutionary model exists
– Lots of work has been done in this area
• Immune system cascade
– This poses no problem whatsoever
– Models to explain the origin of chemical pathways are
abundant
© Colin Frayn, 2008
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Behe at Dover
• In the trial of Kitzmiller vs. Dover Area School District (2005),
Michael Behe testified that several irreducibly complex systems
exist.
Quotes from Judge Jones’s ruling:
“As expert testimony revealed, the qualification on what is meant by ‘irreducible
complexity’ renders it meaningless as a criticism of evolution. In fact, the theory of
evolution proffers exaptation as a well-recognized, well-documented explanation for
how systems with multiple parts could have evolved through natural means.”
“We therefore find that Professor Behe’s claim for irreducible complexity has been refuted
in peer-reviewed research papers and has been rejected by the scientific community
at large.”
“...on cross-examination, Professor Behe was questioned concerning his 1996 claim that
science would never find an evolutionary explanation for the immune system. He was
presented with fifty-eight peer-reviewed publications, nine books, and several
immunology textbook chapters about the evolution of the immune system; however,
he simply insisted that this was still not sufficient evidence of evolution, and that it
was not ‘good enough.’”
© Colin Frayn, 2008
www.frayn.net