Download Sex & Death: Introduction to the Philosophy of Biology

Sex & Death: Introduction to the
Philosophy of Biology
Chapter 4:
The Organism Strikes Back
Overview
The Organism Strikes Back
4.1 What is a gene?
“Evolutionary Gene” fails Invisibility Argument
4.2 Genes are active germ line replicators
First attempt to redefine “gene”
4.3 Genes are difference makers
Second attempt to redefine “gene”
4.1 What Is a Gene?
• Argument against gene selectionism:
• Sober (1984b) distinguishes between
selection for and selection of.
• In gene selectionism only interested in
selection for
Debate on visibility of genes to
selection:
Area 1:
• Explores which DNA
sequences count as
genes
Area 2:
• Explores the
complexity of the
relationship between
the genes and the
phenotypes that they
help to build
Area 1:What is a gene?
• First Definition: a gene is a “reading sequence”
• Second Definition: Dawkins and Williams,
‘evolutionary gene concept’
• Critics object to this second definition since it
does not have a systematic phenotypic
relationship.
What is Phenotypic power?
Two Responses:
1: Molecular genes: genes are functional
biochemical units
2: Genes are “difference makers”
4.2 Genes are active Germ Line
Replicators
Dawkins (1982, 83) and active replicator is:
“any replicator whose nature has some influence
over its probability of being copied”
3 Criteria needed for the invisibility argument:
1) A constant phenotypic effect
2) Excludes impostors like individual
nucleotides
3) The phenotypic effect of genes makes them
more likely to be replicated
4.2 Genes are active Germ Line
Replicators
Problem:
There is not always a constant phenotypic
effect and hence condition one is not met.
But:
There are a few cases where there is a
constant phenotypic effect
4.3 Genes Are Difference
Makers
• There are no genes for traits but for trait
differences
• Despite this being the more commonly used
way of defining genes, it is ambiguous
4.3 Genes Are Difference
Makers
• Disadvantage of viewing genes as ‘difference
makers’ is that it becomes unclear whether they
have an independent reality as a gene
• If this functional definition is not tied to anything
molecular, it cannot be used in favour of gene
selectionism as it speaks against cumulative
selection: this is an empirical problem
Summary:
• Gene Selectionists have tried to formulate
their conception of evolution in a manner
which minimizes its vulnerability to
empirical refutation
• First Attempt: evolutionary concept of
genes
• Second Attempt: Genes as sequences of
DNA that code for specific proteins
Summary:
• Third Attempt: Genes as ‘difference
makers’: I.e. Make a difference in the
phenotypic effect.
• Hence, to prove the gene selectionist view
the empirical and conceptual problems need
to be overcome.