What is adaptation?

• Noun vs. verb (vs. acclimation)• Noun: “…[A] feature is an adaptation for some function if

it has become prevalent or is maintained in a population… because of natural selection for that function” (Futuyma, p.355)

• “… the good fit of organisms to their environment” (Gould & Lewontin, 1979)

• What adaptation is not:• Necessary, perfect, progress, harmonious, moral

BIOL E-127 – 9/24/07

Origin of life

• Definition?:

• Conditions of early earth?:

Origin of life

• Needed components of first organism?:

First metabolism?• Oparin Ocean scenario:

First metabolism?• Autocatalytic cycles (Kauffman):

(Eigen, 1971)

First genetics?• Ultimate chicken & egg…

• Potential answer?

How get enclosure, metabolism & inheritance together?

• One scenario: Lipid world (Segrè & Lancet)

Experimental protocells

• Multiple groups addressing plausibility (Szostak, Rasmussen, Deamer, Luisi)

• Example: RNA adsorbed to clay & encapsulated into myristoleate vesicles

• Can replication provide drive for enlargement? (Chen et al., 2004)

(Hanczyc et al., 2003)

Early history of life

• Constrained by ~4.6 Gya age of planet (or not?)

• Types of evidence?

Chemical evidence of life

• Isotopic enrichment in organic matter

• Banded iron formations (BIFs)

(Madigan & Martenko, 2006)

New metabolisms with O2

• Global analysis of potential of collective biosphere (Raymond & Segrè, 2006)

(Raymond & Segrè, 2006)

Sedimentary textures

• Stromatolites

Fossil evidence of life

• Microfossils in stromatolites:

(Schopf, 1983)

Fossil evidence of life

• Microfossils in stromatolites:

(Schopf, 1983)

Nostoc

Fossil evidence of life

• Microfossils in stromatolites:

(Brasier et al., 2002 )

Fossil evidence of life

• Microfossils in stromatolites:

(Garcia-Ruiz et al., 2003)

(Schopf, 2002)

Fossil evidence of life?: ALH84001

(McKay et al., 1996)

Molecular fossil evidence of life

EryopsOH

OH

OH

OH

FOSSIL SKELETON

H

carbon skeleton with modified stereochemistry

membrane biochemical

Who is it from?

Aquifex

Green sulfur bacteria

Cyanobacteria

Nitrospira

Purple sulfur bacteria

Gram positive bacteria

Green non-sulfurbacteria

Methanopyrus

Methanococcus

Methanosarcina

Halobacterium

Archaeoglobus

Thermoplasma

MethanobacteriumPyrococcus

Pyrobaculum

Thermoproteus

Sulfolobus

Desulfurococcus

Pyrodictium

Thermotoga

Microsporidia

Slime moulds

Ciliates

Plants

Animals

Fungi

Flagellates

Diplomonads

Archaea

Eucarya

Bacteria

rRNA tree modified after Woese

Example molecular fossil: steranes & hopanoids

• Extract & run on GC-MS

• Sterols are eukaryotic specific

• 2-methylhopanoids common in Cyanobacteria

(Brocks et al., 1999; Summons et al., 1999)

Extra references

Brock Biology of Microorganisms, Ch. 11Brocks et al., 1999. Science 285:1033-1036.Hanczyc et al., 2003. Science 618-622.Huber et al., 2003. Science 301:938-940.McKay et al., 1996. Science 273:924-930.Nisbet & Sleep, 2001. Nature 409:1083-1091.Raymond & Segrè, 2006. Science 311:1764-1767.Segrè et al., 2000. PNAS 97:4112-4117.Summons et al., 1999. Science 400:554-557.Smith & Morowitz, 2004. PNAS 101:13168-13173.

When: Wednesday Evening 6:00pmWhere: Second floor lounge of Maxwell-Dworkin, 33 Oxford St. On the Harvard Campus Website: http://www.seas.harvard.edu/projects/weitzlab/squishy.html -------------------------------------------------------------------------------- Sept 26 Irene Chen, Harvard University: Lipid vesicles during the origin of life