COR 401Lecture #11 Mechanisms of

InheritanceFebruary 17, 2009

German biologist/artist Ernst Haeckel (1834-1919),

Moore: If the

hypothesis of evolution

is true, only those

variations that are inherited

will be important

Even Aristotle knew about sex – But how is sex related to

Wallace and Darwin?:

Mechanism of Inheritance

Aristotle’s“Historia Animalium”

~350 BC

Aristotle’s Query:

What is it exactly that parents transmit to their offspring?

Aristotle’sMale Semen/Female Blood

CoagulumTheory

A Cheesy Analogy

Male Semen (bearing “movement”) Sets the Female Semen (bearing

“substance”)

Milk + Rennet = Cheese

Aristotle knew there was something up with the egg

Oviparous Viviparous

Aristotle’s Embryology

Chick EmbryologyTime Lapse

Video

http://www.exploratorium.edu/traits/more.html

48 vs 72 hr Chick Embryos

“Blood is formed out of something that is not blood”

Aristotle’s Theory of Epigenesis

Moore: Parents transmit not structures to their offspring but “information” (p 424)

Pangenesis: Every part of the adult body contributes some specific material to the semen

which then configures the offspring

If so:

How are they packaged to allow for multiple kids?

Why not produce 2 every time?

?

?

Aristotle:Modern

Man in a

Toga?

Fast Forward: 17th-18th C & Preformation

Hartsoeker’s Humunculus (1694)

Malphigi’s 2-Day Chick Embryo

1692

How could structures appear in the course of development from structureless material?

12th C Virgin and ChildTurkey

Epigenesis vs PreformationBut if Preformist Theory is true:

How can offspring be intermediate?

Why this?And

not this?

If both sperm and egg preformed, why not 2 every time?

?

Epigenesis vs PreformationBut if Preformist Theory is true:

How to explain regeneration?

How to conceptualize

Infinite regress?

If all from Eve, what about

Human Variability

What about Dawkins’ Recipe and Blueprint Analogy ?

Which of the Following Statements Best Describes the Analogy:

1. A blueprint is like a scaled down version of an adult, whereas a recipe if obeyed in the right order will

result in an adult.2. The blueprint corresponds one-to-one with the finished product

whereas there is no one-to-one correspondence between recipe and final product.

3. A blueprint implies set purpose and design, whereas a recipe can deviate from the end product depending on the materials and tools available in the kitchen.

4. Of the two, the comparison between epigenesis and recipe is more valid given the strong implication of the importance of

process – it’s all about information driving form/structure

Discovery of cells

Robert Hooke’s Compound Microscope

Discovery of cells

Van Leeuwenhoek’s Simple Microscope

1632-1723

Blending Inheritance:Offspring are an average of parents

Mom Dad

But then where do Darwin’s adaptations come from?

Gregor Mendel 1822-1884

Traits are controlled by heritable “factors” that we now call genes

Summary• Aristotle performed the groundwork in

suggesting that it is information, not structure that is inherited

• Aristotle’s epigenesis was challenged by Pangenesis and Preformist Thinkers

• Microscopes, put Preformist thought to rest • Darwin struggled with Blending Inheritance

as a mechanism by which adaptation would prevail in the struggle for existence.

• But it was Mendel who allowed us to understand the gene and its mode of inheritance.