The document discusses Darwin's argument that similarities in embryos of different organisms provided evidence for common descent. It notes that Darwin and Haeckel observed similarities especially in early vertebrate embryo development. However, later embryologists found that Haeckel's influential drawings exaggerating embryo similarities were inaccurate and that early embryos differ substantially. While common descent remains supported, embryological evidence alone is now considered insufficient.

1. embryology
Argument #4 for Common Descent

2. embryology: case for
Embryology is the study of the development and
formation of embryos.
One of Darwin’s arguments for Common Descent is
based on the similarity of embyros of different
organisms.
Darwin writes, “by far the strongest single class of facts
in favour of” his theory of Common Descent.

3. embryology: case for
Darwin noticed similarities in the embryos of vertebrate
animals especially during the embryo’s earliest stage of
development.
Because of the similarities he concluded 2 things.

4. embryology: case for
1. It established that organisms had descended from a
common ancestor.
He thought that embryos of modern vertebrates are
similar because they evolved from an ancestral form
that had many of the embryonic features of the modern
vertebrates.

5. embryology: case for
2. Darwin thought the observable similarities in different
embryos revealed the ancestors to these organisms
would have looked like.
Darwin said that the embryo “is the animal in its less
modified state”

6. embryology: case for
Ernst Haeckel was a German embryologist and he
popularized Darwin’s 2 main ideas about embryology.
He produced a set of influential drawings showing that
the embryos of various classes of vertebrates were very
similar during their earliest stages of development.

7. Haeckel’s Embryo’s

8. embryology: case for
Modern evolutionary biologists have modified Darwin’s
and Haeckel’s ideas.
They no longer think that embryos reveal the adult form
of their evolutionary ancestors.
Some scientists now think that embryos tell us what
the embryos of their evolutionary ancestors might have
looked like.

9. embryology: case for
online resources
http://www.nyu.edu/projects/fitch/courses/evolution/html/ebryology.html#LectureNotes
http://www.pbs.org/wgbh/evolution/library/04/2/l_042_02.html
http://www.nyu.edu/projects/fitch/courses/evolution/html/embryology.html

10. embryology: a reply
Critics of the argument from embryology agree that
common descent might be a reasonable idea, if the
embryos really were similar in their earliest stages of
development. But, according to most embryologists,
they are not.

11. embryology: a reply
Adam Sedgwich, of Cambridge University, in 1894,
challenged Darwin’s claims.
The embryo’s, of even closely allied animals, such as
chickens and ducks, display specific differences very
early in development.
You can tell the difference between a duck and a
chicken on the second day of development.

12. embryology: a reply
If the early embryos are so different, then why did the
erroneous claim become so popular?
Critics states 2 reasons:
1. Haeckel’s drawings misrepresented the features of
the embryos, he drew them incorrectly, in order to
match Darwin’s theory.
2. Darwin and Haeckel both left out the earliest stage
of development. This is critical because the embryos
are quite different at this stage.

13. embryology: a reply
Haeckel’s drawings became very widespread.
They can be found in many biology textbooks today,
with the claim that the vertebrate embryos are most
similar in their earliest stages.

14. embryology: a reply
In 1997, an international team of scientists, led by
embryologist Michael Richardson, compared
Haeckel’s drawings to photographs of actual
embryos at various stages of development.
They discovered that Haeckel distorted the evidence.
Richardson told the journal Science, “it looks like it’s
turning out to be one of the most famous fakes in
biology.”

15. Richardson’s Picture Comparison

16. embryology: a reply
Stephen Jay Gould wrote, “I think we have the right
to be both astonished and ashamed by the century of
mindless recycling that has led to the persistence of
these drawings in a large number, if not majority, of
modern textbooks.”

17. embryology: 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