Moselio Schaechter


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« TWiM #64: URI and UTI at ICAAC in Denver | Main | The Microscopic Flash Mob »

September 19, 2013

Talmudic Question #100

Past the origin of the first cell, what do you consider to have been the single most important event in evolution?

Comments

Sexual reproduction

Elio, I so admire these Talmudic Questions. We just talked about this in my Microbiology course. Even though I urge (well, hector) students about following STC, I don't believe they do. But I am delighted to report that the students' discussion of this TQ in class was insightful and interesting. The definition of a "cell"---and possible alternatives---was particularly fun. I honestly think an entire seminar course (or a fun book) could be developed from these wonderful questions. Thank you as always.

The death of the last cell.

The first DNA recombination event, whether it be phage mediated or some type of other mobile element i.e. a transposon.

Evolution requires replication, variation and selection. The origin of the first cell was a major event, but the onset of cellular evolution required:
1) The appearance of the second cell (replication)
2) the appearance of the first cell that was different from "The First Cell" leading to variation. This would mark the first mistake in cell replication as a major event.
3) Finally, when the first cellular population reached its niche's carrying capacity after witch not all cells could survive - The beginning of selection.

Genomic tools for dealing with viruses and other mobile elements, and even better, for using their DNA as a source of genetic variation for evolution. Or maybe music ... hard choice :-)

Glad to see a Talmudic question again. Thanks.

one last idea: i don't know why eusocial hymenoptera aren't considered a new phylum! a honeybeehive is certainly a new bauplane!

actually, saying 'first cell' is i think too vague, because it encapsulates many distinct fantastic discoveries... in terms of evolution itself, the fact of discretely different forms (2million++ spp) is what amazes me, beyond the basic life processes themselves. one could try to separate out some properties:

1) the basic machinery that allows a chemical process to feed off of energy flow and hold its form (flames and BZ reaction do this)

2) feedback loops to search for and maintain the process in a flow of energy (like simple bacterial chemo-taxis) (actually involves positive feedback exploratory behavior (random input) and negative feedback loops to zero in on what is found

3) reproduction (a form of positive feedback so the life processes can continue to seek out new environments so a small patch of life doesn't bite the dust in a catastrophic event)

none of these to me so far seems to require discrete cells or discrete forms... and flames ALMOST do all of these...

4) sporulation of a spring loaded chemical mechanism that can hole up under adverse conditions and re-sprout when new conditions arrive. this might have been a stupendous discovery early on that enabled life to survive the early chaotic earth, and enabled life to spread completely across the planet?

5) at this point i can imagine life as an homogenous green goo that can cover the planet and does these things, so the next step is the BEGINNING of Darwinian evolution: encapsulation of discrete heritable forms.

now the genetic apparatus certainly enabled this and is what has catapulted life into its 2million++ amazing forms, but i'm not certain whether chemistry even without encapsulating membranes couldn't do this without the DNA/RNA/Ribosome thingy (well, certainly the lush rainforest of frogs toucans centipedes 600,000 beetles needs the DNA apparatus!). It is one of the areas of chemistry/mathematics that i am currently exploring: what kinds of chemical systems can elaborate into discrete forms

>>now your question was event in evolution, and none of these processes might have been a product of Darwinian evolution, though a fascinating question is how much heredity/selection could have occurred in simple non genetic chemical systems, i.e. proposed auto-catalytic nets even without membrane boundaries? but they fit in the broad meaning of evolution.

6) allied with this concept then, would be eukaryotes' propensity to not share so much DNA as do bacteria and enhance speciation beyond what bacteria seem to me to have done.

7) perhaps some of our rampant speciation (500spp of drosophila in the Hawaiian islands? 600,000++ beetles?) is due to sexual selection and allied mechanisms of reproductive isolation.

8) Homo sapiens/rocket ships to reproduce planets

the woman i waltzed with last weekend!

Maybe sort of a decision of the first cell(s) rather than an event: to stay in contact with the "Ursuppe" and its own siblings via matter (genes, phages, plasmids) and signals (quorum sensing, signal cascades etc.). Without this, the yin-yang interplay of communication and competition would probably not have led to us, studying evolution.

Chemotaxis.

--bks

The birth of Charles Darwin.

Photosynthesis, or at least some form of energy production from light. I don't know what the first incarnations of photosynthesis looked like. There must have been a first protein or useful chemical reaction that was energized by the sun in a reproducible way, that was the most important event in evolution. Later would have come carbon fixation via rubisco, reaction centers and pigments.

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