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Lesson # 1: Evolution
Evolutionary
LESSON # 1: EVOLUTION
Theorists
(EVOLUTIONARY THEORISTS)
JAMES HUTTON (1795)
Scottish Geologist
Geological Gradualism
theory which holds that profound change is the cumulative
product of slow but continuous processes, often contrasted with
catastrophism.
Present earth formed in past by the same processes that act
currently
Long periods of time
 Earth must be millions, not thousands of years old
THOMAS MALTHUS (1798)
English Political Economist
Wrote “An Essay on the Principle of Population” on human
condition as related to overproduction and limited resources
Predicts human population will grow faster than the space
and food supplies needed to sustain it
Species have great powers of potential reproduction
Populations would increase exponentially if all individuals
survived and reproduced
Growing population rates would contribute to a rising
supply of labour that would inevitably lower wages. In
essence, Malthus feared that continued population growth
would lend itself to poverty
JEAN BAPTIST LAMARCK (1809)
 French Invertebrate Natural Historian
 Evolution of Life Forms
When environments change, organisms have to change their behaviour to
survive
 Use / Disuse
Long neck giraffes - if a giraffe stretched its neck for leaves this would make
it longer. Meanwhile organs that organisms stopped using would shrink
 Inheritance of Acquired Characteristics
Believed traits changed or acquired over an individuals lifetime could be
passed down to its offspring (offspring would inherit the longer neck and
continued stretching would make it longer still over several generations)
* Although his theory is flawed he was the first to propose a mechanism
explaining how organisms change over time*
CHARLES DARWIN (1831)
 English Naturalist and child who loved to explore nature
 Embarked on a five year survey voyage around the world on the HMS Beagle
 Darwin collected a variety of natural specimens, including birds, plants and fossils
The Pacific Islands and Galapagos Archipelago were of particular interest to Darwin,
as was South America
 Darwin noticed similarities among species all over the globe, along with variations
based on specific locations, leading him to believe that they had gradually evolved
from common ancestors
 Natural Selection
 Species successfully adapt to meet the changing requirements of where their natural
habitat thrived, while those that failed to evolve and reproduce died off
 A change in the genetic characteristics (allele frequencies) of a population over time
 On November 24, 1859, he published a detailed explanation of his theory in his bestknown work, On the Origin of Species by Means of Natural Selection.
4 STEPS OF NATURAL SELECTION
1) Variation
 Traits differ among individuals in a population
2) Heritability
 Trait differences are passed on to offspring
3) Differential Reproduction
Only some individuals within a generation survive to reproduce and of
those not all survive
4) Darwinian Fitness
Not all produce the same number of offspring
Survival of the Fittest
 Survival of the form that will leave the most copies of itself in
successive generations
CHARLES LYELL (1833)
Scottish Geologist
Wrote “Principles of Geology” Text
Processes occurring now have shaped earths geological features
over a long period of time
Travelled Europe finding much evidence about rising / falling of
sea levels, rock erosion
Uniformitarianism
Current geological processes occurring at the same rates observed
today, in the same manner, account for all Earth’s geological
features
Incorporated Hutton’s gradualism into his widely read book
ALFRED WALLACE (1858)
British Naturalist
Intelligent Evolution
No organ or attribute of an organism will be developed and
retained unless it affords it a survival advantage, where utility
cannot be found in a known organ or attribute, some other cause—
an intelligent cause—must be called upon
Wallace emphasised environmental pressures on varieties and
species forcing them to become adapted to their local conditions,
leading populations in different locations to diverge
Developed a theory of evolution similar to the one Darwin was
working on
GREGOR MENDEL (1854 - 1863)
 “Father or modern genetics”
 Discovered the basic principles of heredity
 Inheritance of certain traits in pea plants follows particular patterns
 How inherited traits are passed between generations
 Mendel worked on pea plants, but his principles apply to traits in plants and
animals – they can explain how we inherit our eye colour and even tonguerolling ability
 Followed inheritance of 7 traits in pea plants that had 2 forms:
Pea shape (round or wrinkled)
Pea colour (yellow or green)
Flower colour (purple or white)
Flower position (terminal or axial)
Plant height (tall or short)
Pod shape (inflated or constricted)
Pod colour (yellow or green)
MENDEL CONTINUED
Mendel developed 3 principles of inheritance based on his experiments
with pea plants.
1) Fundamental theory of heredity
 Inheritance involves the passing of discrete units of inheritance, or
genes, from parents to offspring
2) Principle of segregation
 During reproduction, the inherited factors (now called alleles) that
determine traits are separated into reproductive cells by a process
called meiosis and randomly reunite during fertilisation
3) Principle of independent assortment
 Genes located on different chromosomes will be inherited
independently of each other
THE END!!