Bio. 230 --- Evolution I

Bio. 230 --- Evolution

• “Nothing in Biology makes sense except in the light of evolution.”

• Theodosius Dozhansky (1973)

Evolution Defined (I)

Many definitions, most are OK, some better than othersFrom your text (two definitions):1) “Descent with Modification” (Charles Darwin, emphasizes change)2) “Change in the genetic composition of a population from generation to generation”

(emphasizes genetic change)

Evolution Defined (II)

3) “A change in gene frequency in a population over a period of time” (T. Dobzhansky, 1951, emphasizes change in gene frequencies)

Maybe a little more specific than #2

Evolution Defined (III)

The definition we will use

*4) “The originating of new forms of life from older forms by a process of modification through NATURAL mechanisms” (emphasizes process and ‘natural’)

Hypothesis vs. Theory

Usage varies from field to field and between science and general usage

* Hypothesis --- an educated guess made From preliminary observations

* Theory --- a proposed explanation made in a way consistent with the scientific method and for which we have reasonable supporting evidence (? in ‘everyday” use = fact ?)

Theory

We take a theory as a ‘working’ truth”

Thus: Cell Theory, Evolutionary Theory

It has support (we do not ‘prove’ it)

Even scientific theories can change! WHY?

BAD TERMINOLOGY

Anthropomorphism and Teleology

Fine line between the two

*Anthropomorphism --- attributing of human feeling, emotions, attributes, etc. to other organisms

*Teleology --- attributing of design, purpose or movement toward a goal to natural phenomenaWhy avoid these types of terminology?

EVOLUTIONARY EVENTS ? GEOLOGIC TIME SCALE

A preview

General sequence

Why at these times?

Are the times ‘hard and fast’?

Don’t try to memorize!

Diagrams from text: Table 25.1; Fig. 25.7

ORIGIN OF LIFE

Organic moleculesOn earth or from elsewhere?

LifeOn earth or elsewhere?

Principle of Parsimony (= Occam’s Razor)

PARSIMONYWilliam of Occam – 14th century English logicianWorded a number of ways:Simplest explanation usually the correct one

*“when competing hypotheses are equal in other respects, select the hypothesis that introduces the fewest assumptions and postulates the fewest entities while still sufficiently answering the question”

EARTH / UNIVERSE ORIGIN

1) Universe --- 10 – 20 bya

2) Solar System --- 5+ bya

3) Earth --- at least 4.6 bya

4) Oldest earth rocks --- ~4.1 by old

5) Moon rocks / meteorites --- 5+ by old

6) Why the difference between 4 and 5?

EARLY EARTH

Reducing atmosphere (no O2)

Ammonia, methane, hydrogen, CO2

H2O vapor, maybe CO

No ozone (O3) layerVery strong UV radiationMuch warmerMore violent storms, lightening, etc. than today

ORGANIC MOLECULE FORMATION

Basic inorganic building blocks present

Strong energy sources

“Proper” atmosphere

Plenty of time / area / volume

Then the “unlikely become probable”

ORGANIC MOLECULES AND LIFE

A. I. Oparin (Russian) and J. B. S. Haldane (English), 1920s, independently

Postulated how organic molecules could form

Miller and Urey (1953) and Sidney Fox (1960s) --- Experimental Evidence

MILLER and UREY

Used early reducing atmosphere compounds (basic materials)Heat & Electric spark (energy sources)Obtained complex mixture (sugars, amino acids, nucleic acids, etc.) and polymers of these ABIOGENICALLYSimilar experiments using UV energy or shock waves have produced similar mixturesFig 4.2 from text

OTHER EXPERIMENTS

Charged sites on clay can attract amino or nucleic acids and allow for polymers to form

These polymers are not always random

Metal ions (Zn and Fe) in clay have some catalytic activity (facilitate dehydration reactions)

PRIMORDIAL / HOT SOUP

Early seas became a “Primordial” or hot soup of organic compounds

No free O2 to destroy (oxidize) these compounds

Eventually these compounds formed ‘globules’ with some attributes of cells

Eventually LIFE!

ATTRIBUTES OF LIFE

Metabolism

Irritability

Homeostasis

Reproduction

NONE of these are unique to livings things

PROTOCELLS / FIRST LIFEA. I. Oparin --- CoacervatesForm when oppositely charged colloids are mixed together (e.g. – gelatin & gum arabic)Can concentrate some things from their surroundings (~100x)Add enzymes and some form polymersNot a good model (WHY?)Contemporary proteins, unstable, very variable in size

THERMAL PROTEINOID MICROSPHERES

Need anhydrous and anoxic conditionsThermal proteinoids form on claysWhen added to water they form microspheresSimilar in shape to a coccus bacteriumCan form chainsFairly uniform in sizeFairly stable (even more so when polynucleotides are added into them)

THERMAL PROTEINOID MICROSPHERES

Double layered boundary (? ”membrane”)BUT 2x to 4x thicker than cell membraneGram+ and Gram- microspheresCan sometimes divide by “binary fission” or by budding (similar to yeast budding)First generation “offspring” can grow and divide again

THERMAL PROTEINOID MICROSPHERES

Some display non-random motility

Some can swell or shrink depending on the osmotic conditions

A better protocell model than the coacervates BUT no lipids in the boundary layer

MICELLES

Have membrane-like boundaryCan concentrate substancesHave proteins and lipidsMicelle still not a good protocell modelWHY?Micelles fit the OLD cell membrane model but NOT the newer one

BOTTOM LINE ?????

None of these systems is a ‘perfect’ protocell modelThat may not be importantWhat do these show?From non-living systems / materials things with some properties of life can originate in a rather short period of time

ORIGIN OF LIFE / FOSSIL RECORD

Just a quick overviewDon’t worry about periods / eras at this timeWe will be covering many of these things laterParallels in many things (increase in organism complexity, reproductive modes, etc.) are seen in many groups

GENERAL PHYLOGENETIC “TREES”

Different types of data may yield SOMEWHAT different trees

Usually, however, the overall similarity is quite high

Any really trustworthy tree must be based on data from a number of different sources