Darwin 2.0 ?
Kevin Verstrepen
KU Leuven &
Do new insights in evolution still fit with Darwin’s theory ?
Kevin Verstrepen
KU Leuven &
Just how random is evolution ?
Kevin Verstrepen
KU Leuven &
Darwin 1.0 ?
Kevin Verstrepen
KU Leuven &
Theodosius Dobzhansky
“Nothing in biology makes sense except in the light of evolution”
(How) do organisms evolve ?
‘Great moments in evolution’
Jean-Baptiste Lamarck:
Lamarck´s evolution theory:
selection drives variation
The central problem in studying evolution:
lack of time machines
Darwin
HMS Beagle
Thomas Malthus:
… and selection
“ On the origin of species by means of natural
selection“
Lamarck vs. Darwin
Lamarck
Is variation really independent of selection ?
Just how random is variation ?
Kevin Verstrepen
KU Leuven &
Variation is independent of selection (I)
Max Delbrück en Salvator Luria
Nobel prize (1969)
Luria and Delbrück experiment
Variation is independent of selection Variation is linked to selection
Where does variation originate from?
The “New Synthesis”
“The transforming principle”
The transforming principle
DNA
DNA = ACGTGTTTTAAATTGTTAACAAT TTGGGGCCTATGCGCGCGTATAT ATAGCTGCACGATGCATGATGCT AGCTAGCTAGCTGATCGATGCTA GCTAGGTAGTAGATGATCGTAGT AGTGCTGATGCTCGTAGCTGATG CATGCTAGCTAGCTAGCTGACTG TCACGTAGCTAGCTGCTGCTACG TACGTGAGTAGCTCGTAGCTGAT CGATGCTCGATCGTACGTACGTA GCTGCATGCTACGTACGTAGCTG ATCGATCGTATTTTACGATGCGG GGGGAAAGCTAGCTA…..“It has not escaped our attention that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material.”
DNA can change – “mutations”
DNA = ….ACGTGTTTAAAATTGTTAACA ATTTGGGGCCTATGCGCGCGTAT ATATAGCTGCACGATGCATGATG CTAGCTAGCTAGCTGATCGATGC TAGCTAGGTAGTAGATGATCGTA GTAGTGCTGATGCTCGTAGCTGA TGCATGCTAGCTAGCTAGCTGAC TGTCACGTAGCTAGCTGCTGCTA CGTACGTGAGTAGCTCGTAGCTG ATCGATGCTCGATCGTACGTACG TAGCTGCATGCTACGTACGTAGC TGATCGATCGTATTTTACGATGC GGGGGGAAAGCTAGCTA…..We are all mutants !
Between 2 people: ~ 1 letter per 1000 letters differs
Mutations cause variation
….ACGTGTTTAAAATTGTTAACA ATTTGGGGCCTATGCGCGCGTAT ATATAGCTGCACGATGCATGATG CTAGCTAGCTAGCTGATCGATGC TAGCTAGGTAGTAGATGATCGTA GTAGTGCTGATGCTCGTAGCTGA TGCATGCTAGCTAGCTAGCTGAC TGTCACGTAGCTAGCTGCTGCTA CGTACGTGAGTAGCTCGTAGCTG ATCGATGCTCGATCGTACGTACG TAGCTGCATGCTACGTACGTAGC TGATCGATCGTATTTTACGATGC GGGGGGAAAGCTAGCTA…..Are mutations independent of selection?
Are mutations purely random?
Tandem repeats (= Microsatellite and Minisatellite repeats)
Tandem repeats are known to be unstable
CTTG CTTG CTTG
Tandem repeats as hypervariable genetic modules
Matthieu Legendre Rita Gemayel Marcelo Vinces Verstrepen et al., Nature Genetics 2005
Rando and Verstrepen. Cell 2007
Vinces, Legendre et al., Science 2009
Gemayel et al., Annu. Rev. Genet. 2010
Variable repeats in/near genes increase variation
ORF TR TR TR TR TR TR ORF TR TR TR ORF TR TRRepeats in Runx-2 influence craniofacial parameters
Fondon et al. PNAS 2004
Mutation rates can increase during strong selection
SOS-pathway:
Selection can release hidden variation
HSP 90
releasing hidden variation in times of stress
Tracking evolution as it happens in the lab
Is variation really completely independent of
selection ?
When we look at the DNA level, variation (mutations) do not seem to be completely random…
Our genome has evolved to maximize mutation rates
WHERE and WHEN they are most needed
• Repeats, subtelomeric location, … make certain genes more variable
• HSP90, SOS pathway,… increase variation when it is needed
Variation is not completely independent of selection !
Still; evolution does have a big random component
Motoo Kimura Genetic drift Despite steering
mechanisms, mutations are somewhat random
A newer synthesis …
• Organisms have evolved mechanisms to influence their own evolution
• These mechanisms arose through the principle of variation and selection
• The mechanisms allow some traits to evolve more quickly • The mechanisms allow to increase variability in times of
stress (selection)
• The impact and importance of these mechanisms may vary greatly between organisms, traits and situations.
Death to Darwin ? OR
Back to Darwin ?
Darwin, The Origin of Species, Chapter V:
"I have hitherto sometimes spoken as if the variations ... were due to chance. This, of course, is a wholly incorrect expression, but it serves to acknowledge plainly our
ignorance of the cause of each
particular variation. [The facts] lead to the conclusion that variability is generally related to the conditions of life to which each species has been exposed during several
Death to Darwin ? OR
Back to Darwin ?
Darwin, The Origin of Species, Chapter V:
"I have hitherto sometimes spoken as if the variations ... were due to chance. This, of course, is a wholly incorrect expression, but it serves to acknowledge plainly our
ignorance of the cause of each
particular variation. [The facts] lead to the conclusion that variability is generally related to the conditions of life to which each species has been exposed during several
Which problems did Darwin see in his own theory ?
1. Innovation 2. Cooperation
The problem of innovation in evolution
”[T]he number of intermediate varieties, which have formerly existed on the earth, [must] be truly enormous. Why then is not every geological formation and every stratum full of such
intermediate links? Geology assuredly does not reveal any such finely graded organic
chain; and this, perhaps, is the most obvious and gravest
objection which can be urged against my theory.”
Gene duplication can facilitate
evolutionary innovation
Neofunctionalization
Gene duplication as a catalyst of evolutionary innovation
Voordeckers et al, PLoS Biology, December 11th 2012
Karin Voordeckers Chris Brown Arnout Voet
Steven Maere
Kevin Vanneste
Yeasts can consume many different sugars
MalT
Subfunctionalization or neofunctionalization ?
The position under positive selection explains shift in enzymatic activity M Maltose Isomaltose Pre-mutation Post-mutation
3 Co-evolving residues, one under positive selection
G V G A G M G A S V Q S M Q S V A G G V Q G M Q S M A G 217 - 277 - 278Subtle combination of Ohno´s basic scenario´s
Positive selection Positive selection
The problem of innovation in evolution
”[T]he number of intermediate varieties, which have formerly existed on the earth, [must] be truly enormous. Why then is not
every geological formation and every stratum full of such intermediate links? Geology assuredly does not reveal any
such finely graded organic chain; and this, perhaps, is the
most obvious and gravest objection which can be urged
The problem of cooperation in evolution
‘‘If it could be proved that any part of the structure of any one species had been formed for the exclusive good of another
species, it would annihilate my theory, for such could not have been produced through natural selection’’
The problem of cooperation in evolution
Solution…
William D. Hamilton (“Hamilton’s rule” and Green Beard Genes)
The problem of cooperation in evolution
Solution…
William D. Hamilton (“Hamilton’s rule” and Green Beard Genes)
General conclusions:
• We are entering an exciting time, where the molecular mechanisms that underlie evolution can be studied in detail
• Recent findings show that variation is not completely independent of selection, and that evolution itself generated subtle mechanisms to increase variation where and when it is most needed
• Seemingly novel, innovative features can be evolved by DNA duplication events
• Collaboration can evolve in the framework of kin recognition or green beard genes
• So far, all findings are perfectly in line with Darwin’s theory. No
adaptation is needed; even though we now have a much deeper understanding of the underlying molecular mechanisms.
General conclusions:
• We are entering an exciting time, where the molecular mechanisms that underlie evolution can be studied in detail
• Recent findings show that variation is not completely independent of selection, and that evolution itself generated subtle mechanisms to increase variation where and when it is most needed
• Seemingly novel, innovative features can be evolved by DNA duplication events
• Collaboration can evolve in the framework of kin recognition or green beard genes
• So far, all findings are perfectly in line with Darwin’s theory. No
adaptation is needed; even though we now have a much deeper understanding of the underlying molecular mechanisms.
Darwin Awards
An open question :
Exam questions
1. Compare Lamarck’s theory to Darwin’s
2. Explain the seminal experiment by Luria and Delbruck (including the technical details, outcome, and the larger context)
3. Darwin’s theory has been attacked because it cannot explain innovation. Explain the argument and discuss whether it is a valid criticism, or not.
