Modern biology is based on an understanding of evolution
Why it is important to understand what evolution is
Useful to know its history
How did Darwin and Wallace both discover natural selection at the same time?
Greeks were attuned to the idea that nature changes:
To follow the rise of evolutionary thought one must venture back to the age of ancient Greece, where the idea of essentialism was a belief which explained how natural creatures were what they were. According to essentialist thought, a creature and all of their traits were decided by the amount of the four basic "humors" they had within their body. These humors were Black Bile, Phlegm, Yellow Bile, and Blood. According to the amount of specific humors a person had within their body, they would have specific traits. Accordingly, the Greeks acknowledged that geography was a factor in the traits which were expressed in an organism. For example, a bird from the tropics was brightly colored because it had a specific mixture of humors which were determined by its geography
(slide) As were early Romans such as Lucretius , but "change" went out of fashion when Christianity was adopted
The western belief in linear order— in 18th and 19th century Europe and North America made worth looking for order as a product of God a meaningful pursuit.
Supported feudal social stratification as well as putting everything in its place - we still have strong vestiges of that concept.
Church demand, based on Bible, that nature was fixed, any change was degenerative
Used as justification of existing order and used a mechanism for social control
Difficult to asses that change occurs during a short life span-takes careful observation
People did accept the idea of higher and lower organisms, the higher ones being closer to God
(Slide) Called the scala naturae or ladder of nature, part of the Great Chain of Being (initially developed by Aristotle-)
Example of the ladder of nature with
highest forms at the top and lower forms at the bottom.
| God |
| Angels |
| Man |
| Apes |
| Monkeys |
| Prosimians |
| Other animals |
(Slide) James Ussher (1581-1656), Archbishop of Armagh, Primate of All Ireland, and Vice-Chancellor of Trinity College in Dublin was highly regarded in his day as a churchman and as a scholar.
Of his many works, his treatise on chronology has proved the most durable.
Based on an intricate correlation of Middle Eastern and Mediterranean histories and Holy writ, it was incorporated into an authorized version of the Bible printed in 1701, and thus came to be regarded with almost as much unquestioning reverence as the Bible itself.
Having established the first day of creation as Sunday 23 October 4004 BC, by the arguments set forth in the passage below, Ussher calculated the dates of other biblical events, concluding, for example, that Adam and Eve were driven from Paradise on Monday 10 November 4004 BC, and that the ark touched down on Mt Ararat on 5 May 2348 BC `on a Wednesday'.
His colleague Dr. John Lightfoot, Vice-Chancellor of the University of Cambridge, and one of the most eminent Hebrew scholars of his time, declared, as the result of his most profound and exhaustive study of the Scriptures, that "heaven and earth, centre and circumference, were created all together, in the same instant, and clouds full of water," and that "this work took place and man was created by the Trinity on October 23, 4004 B.C., at nine o'clock in the morning."
See http://www.lhup.edu/~dsimanek/ussher.htm for a more complete description of these two men.
(slide) By early 1700s, beliefs began to decline as science was born
John Ray had introduced species-groups unable to reproduce with each other
Galileo's challenged the church on astronomy
Through the 1600 - 1800's the idea of "The path to God is by contemplating his works" was a romantic and popular one which at least justified (if not motivated) much early natural history work.
Led to great attempts at classifications.
One fundamental problem was - what are the units of life to be classified?
(slide) Last great believer in fixity of species was Linneaus.
Created a taxonomic system for assigning names and groupings to organisms that
is still in use
Linnaeus recognized that interbreeding showed that there was a natural break between organisms that would freely interbreed and those that would not.
- A Swedish naturalist who took it upon himself to classify the entire natural world.
- He became known as "God's Registrar"
In a monumental work on the sexual system in plants Linnaeus showed that the "biological definition of a species" holds true just as well for animals.
- In other words a species is held together by sex.
Nonetheless, in most cases species are recognized by the fact that members of a species tend to look much more like each other than they do to members of other species.Thus, most species are identified by morphology.Species were testable by interbreeding: if they could not interbreed, they were a different species.
He noticed that while the fundamental unit was the species, that species could be grouped by similarity of structure into larger groups: genera, families, orders, classes, phyla, and kingdoms (and others in between).In this "Linnean Hierarchy" are handled specially - a fact you need to know and be familiar with.We call any entity within this hierarchy a taxon (plural - taxa). Thus a species is a taxon, as is a family.
This is an inclusive hierarchy.
In other words, kingdoms consist of and contain classes, classes consist of and contain orders, orders consist of and contain families, families consist of and contain genera, genera consist of and contain species.
(Slide) Here is the Linnean Hierarchy for humans:
Phylum Chordata
Class Mammalia
Order Primates
Family Hominidae
Genus Homo
Species Homo sapiens
In fact, although Linnaeus began by believing that species were fixed entities created by God as is, later in life he began to believe otherwise:They were "children of time", capable of transformation in form though time ÷ in other words species could evolve.
(Slide) Comte de Buffon (Georges Louis Leclerc) published Natural History proposing that species change over time in response to natural laws
By late 1700s, fossils being found challenged the idea of fixity. Extinction is a kind of change, and that could not happen.
(slide) Baron Cuvier and castrophism-explained that evil organisms
perished in catastrophes like Noah's Flood-species could not change themselves.
—a sort of half way between fixity and evolution
Baron Lamarck proposed a real evolutionary theory
Lamarck said animals can change in response natural laws, based on demands of environment.
If animal changed in appearance, that change could be passed on to
offspring-inheritance of acquired characteristics
Soviet Union and Lysenko accepted this idea, holding back advances in evolutionary biology
Charles Darwin's grandfather Erasmus Darwin accepted Lamarck's erroneous ideas, but left open the possibility for other mechanisms
(slide) Advances in geology
James Hutton and Charles Lyell detailed principle of uniformitarianism-present
is the key to the past
Lyell proposed an ancient age for the earth of a million years
(slide) Thomas Malthus Thomas Malthus (1766-1834), an English political economist concerned about the consequences of poverty such as he saw in London. A critical work was his "Essay on the Principle of Population" (1798).
Looked at populations (demography) and observed that organisms produce so many offspring that unless some limiting force was operating, the earth would be overrun.
Concluded that only a small percentage mature and reproduce.
This is a lynchpin notion for evolution. In one sense, it makes evolution inevitable
Two key components to natural selection-differential reproductive success
1. Differential fertility says that the more fertile and individual, the more offspring, and the greater the genetic contribution to the next generation
2. Different morbidity says that those who live longer will produce more offspring and contribute more genetic material
The world could not possibly hold so many, so natural checks are in place.
Poverty, disease, war, and famine were all outcomes of increasing population that in fact kept populations of all organisms from increasing.
Many more organisms are born than can possibly survive.
This is Darwin's notion of "fitness" —refers to the amount of contribution an individual makes genetically to the next generation
Darwin understood that fitness depends partly on environmental condition.
A condition that increases fitness in one environment could be detrimental in another.
(Slide) Charles Darwin and Alfred Wallace came to roughly the same conclusions at about
the same time
Darwin published first--On
the Origin of Species (whole text on line!).
Darwin didn't invent the idea of evolution, he just discovered one mechanism of it
Malthus showed that populations if are allowed to grow unchecked, they increase at a geometric rate.Darwin took this concept and combined it with a critical observation.
The old idea was one of "Ideals" or "Types" of Platonic origin. We still hold to that informally.Variation of morphology and behavior was a fact of life.
In the "typological" concept of species, variation is some error around a true ideal form.
But Darwin recognized that variation was at the core of what a species is.Darwin realized that this natural variation led to differential survival based on that variation.There is a statistically average condition, but each variant is as real as any other and there is no ideal condition.
This concept of type is unfortunately still very much part of racial thinking and has no place in modern biology.
Darwin was espousing "populationist thinking".
For a given environmental context some variants would fair better than others in the "struggle for existence".
Darwin was a domestic pigeon breeder (as a part of his research) and knew that humans had long taken advantage of natural variation to select for breeds; this is artificial selection.
Hence Darwin called his explanation "Natural Selection".
Darwin noted clearly the fact that the most closely related (similar) species were often found closest together in geography.
There are 5 parts to Darwin's Natural Selection:Remember: Populations and species evolve, individuals do not.1. Heredity of most features2. Heritable Variation in the population
3. Variation leads to differential rates in survival and reproductive success among the variations.
4. Differential survival and reproduction leads to a shift in the frequency of characters, leading to a shifting of mode within the species.
5. If this process goes on long enough, parent and daughter species can no longer interbreed.
Two wonderful examples, studied by Darwin and still studied today, are the so-called "Darwin's Finches", members of the family Geospizidae in the Galapagos Islands, and the islands' giant tortises.
Alfred Russell Wallace (1823-1913) came up with vitually the same concept of natural selection more or less independently through his studies on the Malay archipelago. Darwin panicked because he was not ready with his book yet!
Both gave papers at the same time and the same subject at the Linnean Society meeting of 1858 (thanks to Charles Lyell and Joseph Hooker).By the way, the phrase "survival of the fittest" comes originally not from Darwin but rather from Herbert Spencer who adopted Darwin's ideas to a general progessionist philosophy (many say inappropriately), although Darwin adopted the term in his later editions of the Origin of Species on advice from Wallace.
Elements of the lecture above provided by Paul Eric Olsen.