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COR 401 Lecture #11 Mechanisms of Inheritance February 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’s Male Semen/ Female Blood Coagulum Theory
A Cheesy Analogy Milk + Rennet = Cheese Male Semen (bearing “movement”) Sets the Female Semen (bearing “substance”)
Aristotle knew there was something up with the egg Oviparous Viviparous
Chick Embryology Time 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: ? Why not produce 2 every time? ? How are they packaged to allow for multiple kids?
Aristotle: Modern Man in a Toga?
Fast Forward: 17th-18th C & Preformation Malphigi’s 2-Day Chick Embryo 1692 Hartsoeker’s Humunculus (1694) How could structures appear in the course of development from structureless material?
12th C Virgin and Child Turkey
Epigenesis vs Preformation But if Preformist Theory is true: How can offspring be intermediate? And not this? Why this? If both sperm and egg preformed, why not 2 every time? ?
Epigenesis vs Preformation But if Preformist Theory is true: How to conceptualize Infinite regress? How to explain regeneration? If all from Eve, what about Human Variability
What about Dawkins’ Recipe and Blueprint Analogy ?
Which of the Following Statements Best Describes the Analogy: • 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 Dad Mom 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.