1. anatomical homology
Argument #2 for Common Descent

2. anatomical homology: case for
pig n’ arms
A pigs forelimb consists of 3 large bones, the humerus,
radius, and ulna. Our arms contain the same bones.
This raises the question, why should the pig’s forelimb
and my arm have hte same skeletal pattern.
Darwin said these homologies (similarities) were best
explained by this theory of descent from a common
ancestor.

3. anatomical homology: case for
pig n’ arms
According to Darwin and modern evolutionary
biologists, homologies are present in organisms
because they inherited these structures from the
ancestor they had in common.
Humans and pigs both have similar bones in their
forelimbs because we are related and descended from
a common ancestor.

4. anatomical homology: case for
pig n’ arms
What actually gets passed from parent of offspring is
the genetic information, which guides the making of the
forelimb.
Say we have two animals, A and B, which have
homologous structures. The theory of Common
Descent says that they were built by homologous
genes.
Also, the process of growing from an embryo to an
adult (development pathway) are homologous, because
they descended from a common ancestor.

5. anatomical homology: case for
pig n’ arms
According to neo-Darwinism, Natural Selection
modifies genes over time. It also modifies the
embryological processes that produce anatomical
structures (like arms).
Because of these modifications, related organisms
have anatomical structures that are mostly similar, with
a few differences.

6. anatomical homology: case for
pig n’ arms
Common Descent advocates, say that homologous
anatomical structures originated in a common ancestor,
and then were modified by natural selection.
Also, they say that natural selection has modified the
shapes and sizes of bones, and even eliminated some
completely.
Even still, you can see the ancestral pattern in those
structures we recognize today as similar.

7. anatomical homology: case for
as smart as a pig?
It is not only in the skeletal system that homologies are
seen. Similarities can also been seen in soft tissue
structures like the brain and nervous system.

8. anatomical homology: case for
online resources
http://evolution.berkeley.edu/evolibrary/article/0_0_0/lines_04

9. anatomical homology: a reply
Harvard paleontologist Louis Agassiz, long before
Darwin’s time, knew about the existence of
homologous structures.
He explained homologous structures as necessary
because similar structures can solve similar functional
problems.
Cars and airplanes both have wheels, because they
both have to move easily over horizontal surfaces. But
this does not mean that airplanes evolved from cars.

10. anatomical homology: a reply
RDK Thomas and WE Reif have developed an idea
they call “the skeleton space”.
What they mean by this, is that there are only a limited
number of ways that geometric shapes and growing
materials (like bones) can go together and still work
well.
This claims there are a limited number of skeletal
patterns because of the functional requirements of
organisms.

11. anatomical homology: a reply
When 2 or more adult structures appear to by
homologous, neo-Darwinist would say that they would
have been built by homologous development (when the
embryo becomes an adult) pathways and homologous
genes.
Contrary to this, biologists are learning that
homologous structures can be produced by different
genes and may follow different development pathways.

12. anatomical homology: a reply
The wasp and fruit fly are an example of this. They both
have body segments that are homologous.
If they have the same body types because of a
common ancestor, then they should have homologous
genes and homologous development pathways.
Contrary to this, the development of the bodies of
some wasps is completely different than that of the fruit
flies and even other wasps.

13. anatomical homology: a reply
Another discovery that biologists have made, is that in
many cases, the same genes help to produce different
adult structures.
Mouse - single lens camera eye

14. anatomical homology: a reply
Another discovery that biologists have made, is that in
many cases, the same genes help to produce different
adult structures.
Mouse - single lens camera eye

15. anatomical homology: a reply
Another discovery that biologists have made, is that in
many cases, the same genes help to produce different
adult structures.
Fruit fly - compound eye (with dozens of lenses)

16. anatomical homology: a reply
Another discovery that biologists have made, is that in
many cases, the same genes help to produce different
adult structures.
Fruit fly - compound eye (with dozens of lenses)

17. anatomical homology: a reply
Another discovery that biologists have made, is that in
many cases, the same genes help to produce different
adult structures.
Squid - single lens camera eye

18. anatomical homology: a reply
Another discovery that biologists have made, is that in
many cases, the same genes help to produce different
adult structures.
Squid - single lens camera eye

19. anatomical homology: a reply
Each of these eyes develop along very different
pathways and are wired differently from each other, but
the same gene is involved in the development of all 3
eyes.
The Neo-darwinism theory would say that non-
homologous structures should be determined by non-
homologous genes.

20. anatomical homology: a reply
Biologists were shocked to discover this - that non-
homologous structures (eyes) could be caused by
homologous genes.
Stephen Jay Gould called this discovery “unexpected
under usual views of evolution”

21. anatomical homology: a reply
Evolutionary biologists define homology as “similarity
due to common ancestry”.
Question: are there some similarities that are not due to
common ancestry?
Nearly all biologists would say, “Yes”.

22. anatomical homology: a reply
Flippers of a whale and
an ichthyosaur have
similar shapes, but the
whale is a mammal and
the ichthyosaur was a
reptile.

23. anatomical homology: a reply
Flippers of a whale and
an ichthyosaur have
similar shapes, but the
whale is a mammal and
the ichthyosaur was a
reptile.

24. anatomical homology: a reply
Another example is the forelimbs of a mole cricket and a
mole.

25. anatomical homology: a reply
Biologists will tell you that these structures are not the
result of common ancestors. And also that they arose
separately on independent lines of descent.

26. anatomical homology: a reply
resources
Evolution Exposed
by Roger Patterson
Speciation - page 57-67
Homology - page 68-72
Fossils (transitional) - page 73-74
Molecular Homology - page 74-75
Embryology - page 95-96
Refuting Evolution
by Jonathan Sarfati
The Politically Incorrect Guide to Darwinism and
Intelligent Design by Jonathan Wells