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hello my name is lena vincent i'm a phd

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candidate at the university of

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wisconsin-madison

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and in this presentation i'm going to

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share some of the work our lab has been

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doing

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to try to understand how systems

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displaying life's key processes like

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self-propagation and evolution might

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have arisen in the absence of a prior

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living process

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our lab has been using theory and

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experiments to try to resolve this

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mystery

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and to do this we've developed a

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framework to try to explain how

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ecosystems of interacting chemical

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cycles

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could self-organize into systems capable

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of self-propagation and evolution

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and how those systems might further

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complexify and eventually give rise to

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cellular life

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and our hope is that this framework will

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yield insights into the origins of life

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from simple chemical precursors

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now we believe that the ability to

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self-propagate and build complexity

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through adaptive evolution are two

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essential features of life

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and to understand the origins of life we

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have to try to explain

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if and how these processes can emerge

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independently of their specific

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biochemical constituents

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including compartments polymer-based

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genetics and even specific metabolic

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pathways

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now conventional approaches to studying

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the origins of life have historically

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focused on explaining the origins of

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these specific features

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but as a whole they failed to explain

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how those features could have arisen

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spontaneously

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in the absence of a prior living process

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like evolution

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as an alternative the chemical ecology

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model which is the one i'm going to

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present here

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suggests that self-propagation and

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evolution could arise in chemical

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ecosystems

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independently of polymer-based genetics

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and even compartments

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so what is this chemical ecology model

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so to start we define

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chemical ecosystems as sets of

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interacting auto catalytic chemical

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cycles

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and an autocatalytic cycle is simply a

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chemical reaction or sequence of

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reactions

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where at least one chemical species is

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present both as a reactant and as a

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product

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reactant side and that's key

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now we call these member chemicals

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denoted as m or mu

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in the diagrams i'm going to show you

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and these cycles also require

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food or f which are present only on the

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reactant side

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and generate waste w which are only

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present on the product side

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now our lab in an effort led by postdoc

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shen peng

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has simulated reaction cycles of varying

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complexity exposed to constant flux of

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food

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and found that the behavior of even the

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simplest autocatalytic cycles can be

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approximated using logistic growth

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models

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which basically just means that they

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behave much like populations of

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biological species

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even more interestingly when there are

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pairs of interacting cycles that behave

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either as competitors

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mutualists or even predator and prey the

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systems begin to display dynamic

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behaviors

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that resemble ecological interactions

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observed in biological populations

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and these dynamics can be observed as

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changes in the concentration of member

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species over time

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now a key consequence of this chemical

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ecology model is that it suggests that

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chemical ecosystems may be able to

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evolve

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as a result of combinations of different

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ecological interactions among many

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autocatalytic cycles

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as well as random or stochastic

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processes like fluctuations of food

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species or other environmental factors

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so we've also been working to explain

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how natural selection among chemical

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ecosystems

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can take place under plausible prebiotic

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scenarios for example in a sea floor or

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geothermal pool environment

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recognizing that an important component

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of these settings are mineral surfaces

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which have long been implicated in the

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emergence of life as they do things like

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readily absorb or stick to organic

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compounds

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and have important catalytic properties

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chemical ecosystems stuck onto mineral

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surfaces which we endearingly refer to

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as slimes or surface limited molecular

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ecosystems

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could differentially colonize surfaces

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and mutate as a result of rear side

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reactions

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while the continual turnover of mineral

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surfaces can effectively select or

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enrich for slimes

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that are better able to colonize new

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surfaces

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so this model shows us how in principle

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chemical ecosystems could complexify and

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evolve

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without implicating polymer-based

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now an important part of our research

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has been to test this chemical ecology

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model empirically and to do this

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we've developed an experimental

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framework designed to generate and

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detect slimes under laboratory

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conditions

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and we call this chemical ecosystem

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selection

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the basic principle is really simple it

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just involves combining a food-rich

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solution with mineral grains

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and deploying an analog of experimental

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evolution

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and to do this we incubate our

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ingredients to allow for putative slimes

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to establish themselves

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and then we transfer small sepsis

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colonized grains usually about 10

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to a new reaction vessel containing

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fresh food and fresh uncolonized mineral

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grains

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and we repeat this over many generations

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to selectively enrich for variants

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depicted in different colors here in

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this figure

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that are better able to get from green

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to grain and resist

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cereal dilution out of existence now

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importantly we also routinely sample

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both the bulk solution and the mineral

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grains and analyze them to track any

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changes that might be occurring in

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now the nice thing about this approach

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is that it's chemically agnostic

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in that it doesn't presuppose any

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specific chemistry and can therefore be

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used to test virtually any set of

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conditions

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instead the general principle relies on

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the detection of changes in proxy traits

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across generations to infer the

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existence of slimes

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and really the only requirement is that

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the proxy trait be related

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either directly or indirectly to the

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rate of slime propagation

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now response to selection here could

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manifest as a jump in the value of a

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proxy trait over one or several

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generations

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that is then sustained over further

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generations and can be seen here in this

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hypothetical figure

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representing the rate of propagation of

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a slime over time

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whereas progressive evolution would be

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demonstrated by gradual transitions to

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different proxy trait values

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so now to give you specific examples of

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proxy traits we've been using to track

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slime formation in our lab

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and illustrate the chemical ecosystem

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selection procedure a little bit better

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i'm going to show you some results of

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experiments we've conducted in our lab

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so we've screened several sets of

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conditions but for the purposes of this

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presentation

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i'm going to focus on one specific

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recipe we used to validate the approach

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and again chemical ecosystem selection

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doesn't require any specific inputs

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but here we chose ingredients that

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replicate what is known about the early

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earth in some way

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so we used a food rich prebiotic soup

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modeled after

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spark discharge experiments the recipe

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for which can be found in this table

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but you'll also notice that we made

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additions of compounds like atp

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as a chemical energy source although we

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acknowledge that atp

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is not a realistic prebiotic phosphate

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source and for the mineral we used

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pyrite

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and iron sulfide mineral which we ground

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up into powder and cleaned ourselves

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and we carried out the experiment under

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anoxic or oxygen-free conditions

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and we did so on 10 independent lineages

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that were exposed to 40 rounds of

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transfers

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with each generation lasting about two

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to three days and then we analyzed the

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replicate lineages periodically

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with controls that were strategically

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set up to only have a single round of

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transfer in their history

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to isolate the role of these transfers

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one of the selected proxy traits we

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monitored was the concentration of free

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inorganic phosphate in the bulk solution

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at the end of each generation to

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estimate the amount of atp hydrolysis

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that had taken place

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and when we did this we observed a

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distinct oscillatory pattern in the

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amount of free inorganic phosphate

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across generations

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and there are several ways to interpret

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this pattern the simplest being that a

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non-linear or autocatalytic chemical

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system has arisen in response to the

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protocol

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and interestingly the theoretical work

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our group has done

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suggests that these oscillatory patterns

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might reflect the presence of predator

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prey type dynamics and simulated

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chemical ecosystems

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hinting at the possibility that

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interacting or coupled auto catalytic

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cycles might have arisen in our

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experiments

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now on the mineral side we also observe

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distinct fractal structures on the

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surfaces of pyrite grains from samples

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exposed to many rounds of selection

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which are absent or rare in controls

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meaning samples that only have one

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transfer in their history

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and we did these observations by

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electron microscopy and you can see some

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representative micrographs here

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for both experimental and control

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samples and while we're still looking to

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determine the exact composition of these

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structures and their significance

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and whether they're related somehow to

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the source of oscillatory patterns we

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saw in the bulk solution

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this just further illustrates the fact

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that chemical ecosystem selection can be

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used to study complex

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spatial temporal dynamics that can arise

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in prebiotic mixtures

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and while the results i've shown you are

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interesting and consistent with the

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appearance of interacting autocatalytic

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cycles

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much more work is needed to determine

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whether they constitute true slimes by

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our definition

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and for this we would really need to

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demonstrate evolvability and we plan on

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doing this by carrying out experiments

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for much longer

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at least 100 generations and performing

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more in-depth chemical characterization

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and on the theory side our group is

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working to analyze the effects of

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spatial structuring and heterogeneity

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to simulate the effects of mineral

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surface absorption on chemical ecosystem

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dynamics

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which will enhance our ability to apply

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these models in the interpretation of

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results

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that we obtain in our chemical ecosystem

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selection experiments

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so in conclusion we hope that our

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chemical ecology model for the emergence

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of life

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will help advance our understanding of

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life as a general phenomenon

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and shed light on the origins of key

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life processes in relatively simple

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chemical systems

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and i've shown you that our chemical

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ecology model can explain how chemical

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ecosystems of interacting autocathetic

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cycles

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can yield complex dynamics and

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potentially evolve without the need for

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polymer-based genetics or compartments

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and how chemical ecosystem selection

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might help us study the emergence of

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evolvable autocatalysis under laboratory

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conditions

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and we've also already identified a set

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of conditions that yields promising

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results

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and so ongoing and future work in our

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lab will be aimed at further

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understanding and expanding these

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theoretical and empirical models

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and hopefully help the astrobiology

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community as a whole resolve the origins

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and fundamental nature of life

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and with that i'd just like to thank

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past and current members of david baum's

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lab at the university of

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wisconsin-madison

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and wisconsin institute for discovery

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all of our collaborators