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BIOL
4160
Evolution
Phil Ganter
301 Harned Hall
963-5782 |
Arisaema
triphyllum (jack-in-the-pulpit) flowers are an adaptation
only in the presence of insects willing to visit them. |
The Origins of Evolutionary Questions and Theories
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What is Evolution
The popular, short definition is "descent with
modification" which is really to short to make much sense. It
implies important features of evolution rather than explains them.
First, we will use the term in this course as
the equivalent of "biological evolution", as the word has wider application
than biology and without this caveat, we would have to write "biological"
in front of "evolution" each time we use the term.
What evolution is:
- the change in the genotypic and phenotypic characteristics
of groups of related organisms over generations
What evolution is not:
- changes in an organism due to development from
zygote to adult
- Darwinism (refers to evolution by natural
selection, although Darwin was aware of other evolutionary mechanisms)
Evolution and
Biology
Evolution is affected by and effects all
areas of biology - even clinical biology
- Evolution is at the center of several fields
- ecology, bioinformatics, demography, epidemiology to name a few
- Evolution has found uses in other fields in that
it represents a method of searching for optimal solutions
- Some computationally intractable design problems
are amenable to solution through what is known as "evolutionary computation"
Evolutionary ideas current in biology
- Separation of Phenotype and Genotype
- No inheritance of acquired characteristics
- Mutation is random and is the source of genetic
variation required by evolution
- Gradual change is the most common form of change
and can produce great phenotypic differences over geologic time
- Natural Selection, Genetic Drift, (and Sexual
Selection) are the most effective forces in evolution
- Many phenotypic characters are affected by numerous
genes at different loci
Evolution before Darwin -
A selection of those who speculated on the nature of living
things prior to Darwin's book (not intended to be comprehensive in any
sense)
- Some Greeks
- ~520 BC - Anaximander
- speculation
on variability in a species and proposed that species changed over
time
- speculated that life had a single origin
and that it was simpler in the past and has become more complex
- ~500
BC - Xenophanes
- Thought fossils held the key to earlier
form of life and speculated about evolution of living forms
- ~350 BC - Plato and Aristotle
- Plato and Essentialism
- Aristotle and Species as types
- Aristotle and ties to Christian though
- 1686 - John Ray proposed an
early definition of a species and that individuals of a species are similar
due to descent from a common ancestor in his book, History of Plants.
- 1735 - Karl Linne (Carolus Linnaeus)
proposed a hierarchical scheme that he felt revealed a divine order of
living things in his book on classification
- 1749 - Georges-Louis Leclerc, Comte de Buffon proposed a modern definition of species based not on morphological similarity
but
on the ability to produce fertile offspring although he felt that species
were
fixed on a divine scale that, surprisingly, placed man at the summit
- proposed Buffon's Law (later naming), that different
regions have different sets of animals and plants (and so is considered
the father of Biogeography, a subject we will consider later in this course)
- 1770 - Charles Bonnet proposed that
organisms responded to natural catastrophes by evolving (a bit
"natural selection"-ish) and that this evolution followed a pre-determined
path
(not "natural selection"-ish)
- To Bonnet, apes were becoming men and
men were becoming angels as they evolved.
- ~1780 - Immanuel Kant proposed a common
origin for living things and diversification based on need in different
circumstances
- ~1800
- Georges Chrétien Léopold Dagobert (or Jean Léopold Nicolas
Frédéric) Cuvier, a founder of animal paleontology,
was convinced that species go
extinct
but
felt
that
no new species could arise and that evolution was impossible
- argued in a famous paper (1796) on elephants that the bones of a mammoth
were of an extinct elephant species
- Catastrophism - proposed the idea that
catastrophes had caused mass extinctions to explain why fossils
of different strata differed and why the boundaries between strata
were sharp and not
gradual
- never accepted that species could change
through time
- ~1800 - Erasmus Darwin (our guy's granddad)
published Zoonomia, in which he agreed with Anaximander that all
living things were descended from a single ancestor and that they had diversified
into
the
various forms
seen today
due to competition and social interaction
- 1809 - Jean-Baptiste Pierre Antoine de Monet,
Chevalier de la Marck (or Lamarck today) proposes separate origins for
species through spontaneous generation
and subsequent
change by the inheritance of acquired characteristics. Characteristics
changed as our use of them changed and these changes were passed
on to the next generation
- More complex forms has formed earlier
and had more time to become complex.
- each species evolves toward a goal
Important Contributions
from Geology and Social Science to Darwin's ideas
- James Hutton proposed, in Theory of the
Earth; or an Investigation of the Laws observable in the Composition,
Dissolution,
and Restoration of Land upon the Globe (1788), that most geological
change was small (volcanoes and earthquakes were exceptions) and that the
Earth
was
old,
allowing for
great
change
to have
accumulated
(Gradualism)
- Charles Lyell, in Principles of Geology
(1830 to 33, several volume book) championed Gradualism (renamed Uniformitarianism as
opposed to Catastrophism, the idea that geological
change occurs as abrupt, unpredictable events)
and stressed that the forces of geological change seen today
are the
same
as have been
operating since the origin of the Earth,
so we may understand
ancient changes by studying current change and that the future
can be seen as well by studying current processes of change.
- Thomas Malthus, a reverend, economist, and intellectual,
in "An Essay on the Principle of Population" (fist edition in 1798) observed
that
resources
were either
fixed in amount or increased in a linear fashion and that organisms
that used those resources increased not linearly but geometrically
- Felt that all organisms were fated to
experience resource shortage when their capacity for increase caught up
to the amount of resource available
- The inevitable outcome was competition
(accompanied by vice and misery unless tempered by virtue).
Darwin
Background
- Started with the observation that life
has changed over time (evolution as a fact)
- His encyclopedic data were important
in establishing this as a fact, although many biologists and
geologists had documented evolution by Darwin's time
- Accepted descent from ancestor as necessary
part of evolution
- Accepted Gradualism and Uniformitarianism
The Theory (greatly stripped down and focusing
only on natural selection)
- some variation among individuals in a population
is heritable
- some variation among individuals affects the ability
of the individual to survive, grow and reproduce (the fitness of the organism)
- those variations that are both heritable and improve
the individual's fitness will increase in frequency in the population over
generations
Contributions
- Focused on change within populations (which
are still seen as the basic unit in evolution) and documented variation
among individuals within a population
- A population is a local group of interbreeding
organisms
- Argued that very large differences between the
morphologies and anatomies of living species was achieved through a process
of small changes in populations accumulated over long periods of
time
- Tree of Life - Proposed that the history
of life was a branching process, in which new branches are new species
(or
lineages)
derived from
ancestral species (this idea is closely related to his idea that evolution
is gradual but is not dependent on gradualism)
- Proposed Natural
Selection as the mechanism by which evolution proceeds
- Natural selection is the outcome of the inheritance
of beneficial forms of a trait within populations that vary for that trait
Evolution Soon After
Darwin
Darwin's mechanism was not immediately
accepted, although his documentation of variation and change convinced biologists
of the fact of evolution
Many years of speculative theorizing about
mechanism of evolution
- Neo-Lamarckianism - acquired characteristics
regained popularity but A. Weismann demonstrated that cutting the tails
off of mice never became an inherited characteristic
- Orthogenesis - disagreed that the environment
set the course of evolution, especially over long periods and at higher
taxonomic levels
- they felt that organisms progressed toward
a set goal over time (this sort of idea is very old - remember Lamarck's
idea that all species begin as simple organisms and progress in complexity
toward their ultimate destiny)
- Mutationism - Mutationists
felt that evolution occurred in discrete jumps (remember, mutation had
very different connotations
before the rise of genetic and the discovery of DNA as the heredity molecule)
- New species originated when they mutated from
pre-existing species, but this process was independent of natural selection,
which only affected the composition of populations (below the species level)
Evolution Since 1900
- Twentieth Century Evolution
- Mendel represented
a challenge to Darwin's gradualism
- Mendelists (Saltationists, Mutationists
- Wm. Bateson, H. de Vries) claim that Mendel showed that genetic
change was discrete and sudden, not continuous and gradual as Darwin
proposed (data from discrete
characters)
- Biometricians (Francis Galton, Karl
Pearson, WFR Weldon), who used different models of evolution, claimed
that
genetic change
was
gradual
and continuous (data from multifactorial characters)
- Modern (Evolutionary) Synthesis of
Mendelism and Evolutionary Theory
(R. A. Fisher, J. B. S. Haldane, Sewall Wright)
- Response to controversy, developed models
of evolution of discrete mutations that resulted in evolutionary
change consistent with Darwin's
predictions of gradual change and that discrete mutations could lead
to continuous change if multiple loci affected the character
- Population Genetics developed
from modeling of evolution of genes in populations
- Quantitative Genetics developed from
modeling of inheritance of multi-factorial phenotypes
- Important books appeared that dealt
with evolution and speciation (E. Mayr, T. Dobzhansky), evolution
in
plants (G. Ledyard Stebbins), evolution and paleontology (G. G.
Simpson),
and evolution
and adaptation (T. Dobzhansky)
- Molecular Biology was incorporated
into Darwinian theory
- J. Crow and M. Kimura introduced Neutral
Theory of Evolution
- wealth of discoveries about genes
and genomes integrated into genetic theory
- jumping genes, transposons, DNA duplications,
epigenetic effects
- Punctuated Equilibrium and Paleontology
- Twenty-First Century Evolution - evolution in
every aspect of biology
- Evolutionary Genomics
- Evolutionary Historical Ecology
- Evolutionary Developmental Biology
Last
updated January 11, 2012
