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 arevolutionary process

“normal” science

anomalies

scientific “revolution”

Normal Science ca. 1600the 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 Linneausby M. Hoffman in 1734.

Carolus Linnaeus 1707-1778

• Systema Naturae (1735, with many subsequent revisions)

• Standardized names of plants and animals

Binomial nomenclatureWedding Portrait of Linnaeus

(1739)

Carolus Linnaeus 1707-1778

Before, the common wild briar rose was known variously as

• Rosa sylvestris inodora seu canina

• Rosa sylvestris alba cum robore, folio glabro

Using binomial nomenclature, names were standardized:

• Rosa canina

• 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 Cuvier1769-1832

• “Father” of comparative anatomy

• Studied the anatomy of vertebrates

• Established the field of vertebrate paleontology

Georges Cuvier1769-1832

• 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 Lamarck1744-1829

• 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 Hutton1726-1797

• 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 Hutton1726-1797

• Pointed out role of erosion

• Earth was timeless

• A self-perpetuating place created for humans

• No directional change, only cycles

Charles Lyell1797-1875

• 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 Lyell1797-1875

“uniformitarianism”

• Excluded the use of sudden catastrophes when explaining fossils

• Earth was extremely old

Thomas Malthus1766-1834

• 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 Malthus1766-1834

"population increases in a geometric ratio,

while the means of subsistence increases in an arithmetic ratio."

food supply

population

Adam Smith1723-1790

• 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 Smith1723-1790

• 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 DarwinFeb. 12, 1809 – April 19, 1882

• father and grandfather were physicians

• an avid insect collector from an early age

• December 1827begins 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

• Develops his own ideas about natural selection

• Sends Darwin a manuscript in 1858

Alfred Russel Wallace(1848)

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

• Includes evidence from– His insights into insects

and other organisms– Distribution of organisms– Fossil record– Embryology– Comparative anatomy– Comparative behavior– and, and, andDarwin at Down House,

ca. 1880

November 24, 1859

• First edition sells out the first day

• Acceptance in scientific circles is rapid

• Makes no reference to evolution of humans

 

ON

THE ORIGIN OF SPECIESBY MEANS OF NATURAL SELECTION,

OR THE

PRESERVATION OF FAVOURED RACES IN THE STRUGGLEFOR 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.

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 Selection1. 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

Artificial

• requires

• a trait to exhibit variation

• and a selective pressure

Natural

• requires

• a trait to exhibit variation

• and a selective pressure

The selective pressure is exerted by humans

The selective pressure is exerted by the

environment (nature)

The Three Problems1. 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 Mendel1822-1884

• 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

If you bred a white-flowered plant with a red-flowered plant, you will obtain a

plant with either white or red flowers

Blending

If you bred a white-flowered plant with a red-flowered plant, you will obtain a

plant with pinkish flowers

Pisum sativum

Trait Forms

seed form smooth wrinkled

albumen color 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 femalessperm, pollen for males)

Pisum sativum

Trait Dominant Recessive

seed form smooth wrinkled

albumen color 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

genes alleles

Mendel’s First Law

The Principle of Segregation

Alleles exist in pairswhich are separated from one

anotherduring the production of gametes

this means that…

…the chances of any particular outcome can be predicted!!!

Inheritance occurs according tostatistical 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 Problems1. 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?