Transcript Darwin, Mendel, and the Rise of the Synthetic Theory

Biological Anthropology
Darwin, Mendel, and
The Rise of the Synthetic Theory
Three Questions to Answer
1. Where does variation come from?
2. How is variation passed on from one generation to
the next?
3. How is the variation present within a species at any
time affected by the environment?
Science as a
revolutionary process
scientific “revolution”
anomalies
“normal” science
Normal Science ca. 1600
the origin of living things
• Great Chain of Being
• Held in the hand of God
• Ranked living things as more or
less like God
• Links represent species
• Discrete
• Immutable
Carolus Linnaeus
1707-1778
• Son of a Lutheran pastor
• Groomed to be a pastor
• Preferred science
• Became a physician and
botanist
Carl Linneaus
by M. Hoffman in 1734.
Carolus Linnaeus
1707-1778
• Systema Naturae (1735,
with many subsequent
revisions)
• Standardized names of
plants and animals
Binomial
nomenclature
Wedding Portrait of Linnaeus
(1739)
Carolus Linnaeus
1707-1778
Before, the common wild briar
rose was known variously as
Using binomial nomenclature,
names were standardized:
• Rosa sylvestris inodora seu
canina
• Rosa canina
• Rosa sylvestris alba cum robore,
folio glabro
• Coffea arabica
• Homo sapiens
Carolus Linnaeus
1707-1778
• First believed species were
immutable
• Noticed hybrids
• Observed that plant species could
change appearance as they
acclimatized to new areas
• Eventually abandoned idea of fixity
of species
Georges Cuvier
1769-1832
• “Father” of comparative
anatomy
• Studied the anatomy of
vertebrates
• Established the field of
vertebrate paleontology
Georges Cuvier
1769-1832
• Noted distinct differences
between fossil mammoth (top)
and living Indian elephant
(bottom)
• Discovered that species could go
extinct
from Cuvier's 1796 paper on
living and fossil elephants
What had happened to these animals?
• Periodic “revolutions” or catastrophes had befallen
the earth
• These were events that had natural causes
• Although Cuvier did not identify these with Biblical
events, others would
Jean-Baptiste Lamarck
1744-1829
• Studied invertebrate anatomy
• Saw a relationship between an
animal’s form and the way it
exploited the environment
• Argued that a change in the
environment could affect the
needs of the organisms in that
environment, causing them to
alter their behavior
Lamarck said
• Altered behavior led to more or
less use of a body part, which
would therefore grow larger or
smaller
• Such changes are inherited
A great idea!
But it’s wrong!
James Hutton
1726-1797
• Scottish geologist
• A cyclical “world machine” that
exhibited “no vestige of a
beginning – no prospect of an
end.”
• This view ultimately led to
modern geological time scales
James Hutton
1726-1797
• Pointed out role of erosion
• Earth was timeless
• A self-perpetuating place
created for humans
• No directional change, only
cycles
Charles Lyell
1797-1875
• Another Scottish geologist
• Principles of Geology
(3 Volumes; 1830-1833)
• Argued that currently active
principles were all that was
needed to explain the
geological history of the Earth
Charles Lyell
1797-1875
“uniformitarianism”
• Excluded the use of sudden
catastrophes when explaining
fossils
• Earth was extremely old
Thomas Malthus
1766-1834
• An Essay on the Principles of
Population (1798)
• Points out that more
individuals are born into a
species than will ever reach
maturity
• A struggle for survival
Thomas Malthus
1766-1834
"population increases in a
geometric ratio, while the
means of subsistence
increases in an arithmetic
ratio."
food supply
population
Adam Smith
1723-1790
• An Inquiry into the Nature and
Causes of the Wealth of Nations
(1776)
• Laissez-faire economics:
markets perform best if allowed
to function according to their
own principles
Adam Smith
1723-1790
• Smith’s ideas inspired Darwin
in a more general way:
• A system, once established,
will run itself according to its
own principles
• A system does not require a
higher authority to regulate a
system itself
Charles Robert Darwin
Feb. 12, 1809 – April 19, 1882
• father and grandfather were
physicians
• an avid insect collector from an
early age
• December 1827
begins to study for the clergy at
Christ's College, Cambridge
• Bachelor of Arts degree in April,
1831
Charles Darwin
• Invited to serve
as ship’s
naturalist on
H.M.S. Beagle
The Second Voyage of the Beagle
Departs England on 27 Dec., 1831 – Returns to England on 2 October, 1836
The Post-Beagle Period
• Darwin settles into a comfortable
life
• Publishes numerous books
• Breeds pigeons
The Post-Beagle Period
• 1838-1844 – serves as Secretary
of the Geological Society of
London
• Becomes friends with Charles
Lyell
• 1837 - first mention of the
“transmutation” of species in his
notes
From Darwin’s notes – ca. 1838
Alfred Russel Wallace
• Studies the distribution of
animals in the Malay
Archipelago
Alfred Russel Wallace
(1848)
• Develops his own ideas
about natural selection
• Sends Darwin a
manuscript in 1858
July 1, 1858
• Ideas of each presented at a meeting of the Linnean Society
• both credited with the idea of natural selection
Darwin gets Busy!
• Write “short” version of his
ideas
Darwin at Down House,
ca. 1880
• Includes evidence from
• His insights into insects and
other organisms
• Distribution of organisms
• Fossil record
• Embryology
• Comparative anatomy
• Comparative behavior
• and, and, and
November 24, 1859
ON
THE ORIGIN OF SPECIES
BY MEANS OF NATURAL SELECTION,
• First edition sells out the first
day
OR THE
PRESERVATION OF FAVOURED RACES IN THE STRUGGLE
FOR LIFE.
BY CHARLES DARWIN, MA.,
FELLOW OF THE ROYAL, GEOLOGICAL, LINNAEAN, ETC., SOCIETIES;
AUTHOR OF 'JOURNAL OF RESERACHES DURING H.M.S. BEAGLE'S
VOYAGE
ROUND THE WORLD.'
LONDON :
JOHN MURRAY, ALBEMARLE STREET.
1859.
• Acceptance in scientific
circles is rapid
• Makes no reference to
evolution of humans
From the final paragraph…
“There is grandeur in this view of life, with its several
powers, having been originally breathed by the Creator into
a few forms or into one; and that, whilst this planet has gone
cycling on according to the fixed law of gravity, from so
simple a beginning endless forms most beautiful and most
wonderful have been, and are being evolved.”
Later Works
• The Descent of Man, and
Selection in Relation to Sex
(1871)
• The Formation of Vegetable
Mould through the Action of
Worms, with Observations on
Their Habits (1881)
Natural Selection
1.
At any one time, more individuals are born into a species than will
survive
2.
Each individual is unique (that is, different from the others)
3.
Some of these differences may be advantageous in the environment in
which the individual lives, while others may
be disadvantageous
4.
The individuals with the advantages are more likely to survive and
reproduce than the individuals with the disadvantages
5.
Over time, the advantageous traits become more common, and the
disadvantageous traits become less common
Microevolution
...and there’s nothing controversial about that
Macroevolution
…if the process continues long enough, you
can end up with entirely new species
And that’s what some people object to
Two Types of Selection
• requires
Artificial
• requires
Natural
• a trait to exhibit variation
• a trait to exhibit variation
• and a selective pressure
• and a selective pressure
The selective pressure is
exerted by humans
The selective pressure is
exerted by the
environment (nature)
The Three Problems
1. How is the variation present within a species at any
time affected by the environment?
Darwin
2. How is variation passed on from one generation to the
next?
3. Where does variation come from?
The Next Piece of the Puzzle
Gregor Mendel and
The Mechanisms of Inheritance
Gregor Mendel
1822-1884
• Entered the Augustinian
monastery of St. Thomas at
Brnø at 22
• Ordained as priest in 1847
• Taught secondary school
science
Two ideas about inheritance
Particulate
Blending
If you bred a white-flowered
plant with a red-flowered
plant, you will obtain a plant
with either white or red
flowers
If you bred a white-flowered
plant with a red-flowered
plant, you will obtain a plant
with pinkish flowers
Pisum sativum
Trait
seed form
albumen color
Forms
smooth
wrinkled
yellow
green
seed coat color
gray
white
seed pod form
inflated
constricted
unripe pod color green
yellow
flower position
axial
terminal
stem length
tall
dwarf
What Mendel Discovered
• Each plant contained two
pieces of information for a
particular trait
• Some of these were dominant,
some recessive
• Each parent contributed only
one piece of information to
each of their offspring
Some terms…
• Gene – unit of hereditary information for
a particular trait
• Allele – alternate form of a gene
• Gamete – a sex cell (egg for females
sperm, pollen for males)
Pisum sativum
genes
alleles
Trait
seed form
albumen color
Dominant Recessive
smooth
wrinkled
yellow
green
seed coat color
gray
white
seed pod form
inflated
constricted
unripe pod color green
yellow
flower position
axial
terminal
stem length
tall
dwarf
Mendel’s First Law
The Principle of Segregation
Alleles exist in pairs
which are separated from one another
during the production of gametes
this means that…
…the chances of any particular
outcome can be predicted!!!
Inheritance occurs according to
statistical probabilities!
Mendel’s Second Law
The Principle of Independent
Assortment
The distribution of alleles for one trait
does not affect the distribution of alleles
for another trait
Independent
Assortment
• Whether an individual
inherited one particular
trait from its father did
not affect whether it
inherited a different trait
from the father as well
• It’s a crapshoot!
The Synthetic Theory of
Evolution
Variation is passed down according to
Mendelian principles
and selected for or against
according to Darwinian
principles
What are the physical
mechanisms through which
traits are passed on?
Particulate or Blending?
The answer depends upon:
•the trait being studied
•the species it is being studied in
In Humans?
Over 4500 known
“particulate” traits
• ABO blood group
• Rh blood group
• Cystic fibrosis
• Cerumen
• Sickle-cell
• PTC tasting
Numerous
“blended” traits
• Height
• Weight
• Intelligence
• Skin color
• Eye color
The Three Problems
1.
How is the variation present within a species at any time affected by the
environment?
Darwin
2.
How is variation passed on from one generation to the next?
Mendel
3.
Where does variation come from?