EES 227: Paleobiology

Spring 2004

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Lecture 6: February 12 2004: Darwin Day

Reading:

Web resources for this lecture:

Lecture Notes: Evolutionary Theory.

Before Darwin:

A popular view of nature was 'Natural Theology' (e.g., Linnaeus ), as contrasted with 'revealed theology' where insight in the nature of the deity is arrived at without observations. Natural Theology was very popular in the 1700s, and implies:

Natural theology:

But from the 1700s on: decreasing believe in Bible as literally true

Lamarck (1744-1829):

NOTE: Pasteur lived 1822-1895; the argument on the theory of 'spontaneous generation' (origin of life from non-life) ran from 1668 through 1859 when Pasteur did his winning experiment. For insatnce, a seventeenth century recipe for the spontaneous production of mice required placing sweaty underwear and husks of wheat in an open-mouthed jar, then waiting for about 21 days, during which time it was alleged that the sweat from the underwear would penetrate the husks of wheat, changing them into mice.

Debate started seriously in 1668 by Francesco Redi (no maggots on meat covered with fine netting, in closed jar). But invention of microscopy seemingly supported spontaneous generation, revealing a whole new world of organisms that appeared to arise spontaneously. It was quickly learned that to create "animalcules," as the organisms were called, you needed only to place hay in water and wait a few days before examining your new creations under the microscope.

Lamarckianism (or 'adaptation on demand'); what we now call Lamarckianism was really only a very small part of Lamarck's book.

Note that organisms themselves 'strive to change'. Darwinian ideas and modern dogma of biology: efforts by parents not inherited by their offspring.

Charles Darwin, 'The Origin of Species' (1859); [1809-1872]

"I had two distinct objectives in view;

Things that were NOT Darwin's idea:

Components of Darwinism as Darwin knew it:

Natural selection:

What Darwin did not know about:

Neodarwinism: 'The Modern Synthesis':

Afterwards modified: structure of genetic material (DNA-RNA) 1953 (Watson & Crick)

Separation of body cells (somatic cells) and reproductive cells (germ cells): Weisman's barrier'. Later this was redefied as the 'central dogma of biology': DNA => RNA => protein (transcription)

Natural Selection and Genes

What is Evolution?

Oxford Concise Science Dictionary: Evolution: "The gradual process by which the present diversity of plant and animal life arose from the earliest and most primitive organisms, which is believed to have been continuing for the past 3000 million years." NOTE: definition requires 'gradual': not accepted by everyone.

New Webster Encyclopedic Dictionary of the English Language: "Evolution: ...that theory which sees in the history of all things, organic and inorganic, a development from simplicity to complexity, a gradual advance from a simple or rudimentary condition to one that is more complex and of a higher character". NOTE: definition requires 'progress'; would exclude evolution of parasites that e.g., lack eyes from ancestors that have them

" Biological evolution ... is change in the properties of populations of organisms that transcend the lifetime of a single individual. The ontogeny of an individual is not considered evolution; individual organisms do not evolve. The changes in populations that are considered evolutionary are those that are inheritable via the genetic material from one generation to the next. Biological evolution may be slight or substantial; it embraces everything from slight changes in the proportion of different alleles within a population (such as those determining blood types) to the successive alterations that led from the earliest proto-organism to snails, bees, giraffes, and dandelions." (Douglas Futuyma)

Definition MUST contain:

Some Terms:

Organisms with a specific allele are doing better than those with a different allele. The allele whose possessor does better will become more and more common in the population, because the organisms which carry the favorable allele are leaving more offspring.  Alleles that make their possessor less able to reproduce than other organisms of the same species will disappear from the total population.

What happens during evolution?

Evolution: more definitions:

'Evolution is a process that results in heritable changes in a population of organisms, which changes are spread over many generations'. Note that this definition lacks such terms as 'gradual', or 'to more complex forms'!

This contrasts with a much more limited definition (Neodarwinian) of evolution as seen, e.g., in some high school text books:

"In fact, evolution can be precisely defined as any change in the frequency of alleles within a gene pool from one generation to the next."

Many scientists, however, including many paleontologists and embryologists would disagree with this definition: "Evolution is change in gene frequencies"

What some people do not like about strict Neodarwinianism (as e.g., argued for by Richard Dawkins) and specifically the statement that evolution is a change in gene frequency are the following aspects:

Why does evolution occur? What drives evolution? What is the limiting factor on the rate of evolution?

What drives evolution?

Arguments against strict Neodarwinism from within biology/genetics:

Arguments against strict Neodarwinism from within Paleontology.

Punctuated Equilibrium: