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Evolution, Genetics, and Psychology Charles Darwin1809-1882

Darwin provided biology with its great unifying principle:

“The Theory of Natural Selection”

EvolutionPre-Darwinian views

Doctrine of Progression

The world is full of as many diverse forms as it can be.

Each species exists because of a special creation by God. One species could not be derived from another.

Each species is a pre-ordained type. Variation is due to error, in some cases pathology.

But how does one explain fossils and other apparently extinct species?

World cataclysms -- like the Great Flood.

and the answer is….

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The continuity of existing forms -- from inanimate to animate, from plants to animals to man and God was part of the Great (Ascending) Chain of Being.

Near the top of the Chain was Western European Man, just below God him (her) self

An obvious ally in this view was the Christian Church.

Doctrine of Progression A Problem for the Doctrine of Progression

Sir Charles Lyell1797-1875

In his 1830 book, “The Principles ofGeology”, Lyell argued that the earthwas extremely old and that instead ofa series of catastrophes, the same

natural forces seen at work today -- volcanoes, earthquakes, wind, frost, rain -- were those that had shaped the earth in the past. These were the “uniform sources” of geological history.

Uniformitarian Geology introduced the idea of endless time -- the idea that the earth was millions of years not merely a few thousand years old.

Darwin was not the first person to advocate the idea of evolution

Even his grandfather,Erasmus Darwin, was an evolutionist – and believed that humans evolved from simpler forms.

1731-1802

Organic life beneath the shoreless wavesWas born and nurs'd in ocean's pearly caves;First forms minute, unseen by spheric glass,Move on the mud, or pierce the watery mass;These, as successive generations bloom,New powers acquire and larger limbs assume;Whence countless groups of vegetation spring,And breathing realms of fin and feet and wing.

Erasmus Darwin. 1802

The Temple of Nature Other Evolutionists

• use and disuse leads to change

• movement toward perfection• changes in form through conscious will

• environmental effects on organ development

The French naturalist, Jean-Baptiste Lamarck (1744-1829), introduced the idea of the inheritance of acquired characteristics.

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Darwin advocated the idea of Natural Selection

Darwin’s father, Robert Darwin, was a successful country physician

Darwin’s mother was Susannah Wedgewood, the daughter of Josiah Wedgwood, founder of England's world-renowned Wedgwood pottery.

In 1825 at age 16, Darwin was sent off to Edinburgh to study medicine, but he hated it.

Charles scarcely knew his mother who died when he was eight.

Charles and his younger sister, Catherine

He loved to collect plants, insects, and geological specimens, under the guidance of his cousin, William Darwin Fox, an entomologist.

Darwin then was enrolled in Christ’s College Cambridge to study theology.

Darwin was encouraged by his botany professor, John Stevens Henslow, who secured for him a space on the HMS Beagle.

Darwin spent from 1831 to 1836 on the Beagle visiting Cape Verde Islands, Brazil, Montevideo, Tierra del Fuego, Buenos Aires, Valparaiso, Chile, the Galapagos, Tahiti, New Zealand, and Tasmania.

Captain Robert Fitzroy

1805-1865

Darwin was impressed with fossils in Patagonia Darwin was also amazed at the diversity of life in the Galapagos Islands.

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…particularly the different species of giant tortoises living on the different islands of the Galapagos.

It is often said that Darwin was struck by the fact that there were 13 different species of finches in the Galapagos, each of which had a beak shape and size that was adapted to its particular ecological niche.

Darwin’s Finches

Adaptive radiation from a common ancestor

Over the seven years of the voyage, Darwin collected all kinds of specimens, which Fitzroy described as “cargoes of apparent rubbish.”

After Darwin returned to England in 1837, he never went abroad again.

In 1839, he married his cousin, Emma Wedgwood, and moved to a country house in Kent (Down House) where he spent the remaining 40 years of his life.

Darwin began to write a series of impressive works in biology and geology, many of them based on his experiences on the Beagle.

Sir Charles Lyell

1797-1875

Darwin became friends with Sir Charles Lyell.He had already been influenced by Lyell’sideas on the great age of the earth.

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In October 1838, Darwin read Thomas Malthus' An Essay on the Principle of Population.Malthus argued that population growth is geometric, while the food supply increases only arithmetically. Thus, population increase is always checked by a limited food supply.

Thomas Robert Malthus1766-1834

Darwin realized that given the struggle for existence everywhere, "favourable variations would tend to be preserved, and unfavourableones to be destroyed. . . . The result of this would be the formation of new species.”

But Darwin did not publish his developing ideas on natural selection until 1859.

Darwin was eventually prompted into action by a letter he received from Alfred RusselWallace in 1858 in which Wallace outlined a similar set of ideas.

Alfred Russel Wallace1823-1913

Darwin agreed that he and Wallace would present a short paper together at the Linnean Society in 1858. Finally, after years of sitting on his ideas, Darwin (urged by his colleagues) published “The Origin of Species” in 1859.

All 1500 copies sold out on the first day!

But what is the Theory of Natural Selection?

Three Inductions and two Deductions

Induction 1: Organisms have an enormous capacity to overproduce.

Induction 2: Populations (with a few exceptions) remain remarkably stable.

Deduction 1: There is a struggle for survival.

Induction 3: Individuals differ in their characteristics and many of these differences are heritable.

Deduction 2: Those individuals who possess adaptive characteristics will reproduce more successfully than those who don’t and will pass on these characteristics to their offspring.

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Deduction 2: Those individuals who possess adaptive characteristics will reproduce more successfully than those who don’t and will pass on these characteristics to their offspring.

This last process is what Darwin meant by ‘Natural Selection’.

Evolution can be seen as the accumulation of the changes in the population due to natural selection.

These ideas were embraced by many in the scientific community – but not by everyone – and certainly not by the Church.

Samuel WilberforceBishop of Oxford

1805-1873

Thomas H. Huxley1825-1895

Darwin’s Bulldog vs. Soapy Sam at the meeting of the British Association at Oxford in 1860.

``Is it on your grandfather's or your grandmother's side that you claim descent from a monkey?''

“I am not ashamed to have a monkey for an ancestor; but I would be ashamed to be connected with a man who used great gifts to obscure the truth.”

Upon hearing about Charles Darwin's The Origin of Species, the alarmed wife of the Bishop of Worcester exclaimed “Descended from the apes! Let us hope that it is not true. But if it is, let us pray that it may not become generally known.”

Herbert Spencer1820-1903

Social Darwinism

The ‘Survival of the Fittest’ applied to human society at large.Spencer argued that evolutionary theory could provide a basis for a comprehensive political and even philosophical theory.

Societies evolve from lower (barbarian) to higher (civilized) formsSurvival of the fittest: the most capable survive, the leastcapable die out

It’s wrong to interfere with this process

These ideas prevailed in some circles well into the 20th C

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Christian reaction to Darwin

“Creationism”

“...logic does not require that man evolved from a fish just because finches on the Galapagos islands have beaks which vary from each other. Fishes are not men, and men are not fishes, but finches are still finches. Fish and men are in different kinds as delineated in the Bible. Variations within finches are still within the bird kind and as such they do not cross the barrier of kinds. Hence, proving variation within finches has proven absolutely nothing which cannot have taken place within Biblical limits.”

‘A Creationist’s View of Darwin’s Origin’Timothy Stout

Intelligent DesignThe publication of Darwin’s “The Origin of Species” in 1859 had an enormous effect on ideas about human behaviour.

Fifty years later, the re-discovery of the work of Mendel on inheritance led to the development of Mendeliangenetics and a mechanism whereby natural selection could operate.

Gregor Mendel (1822-1884) was an Austrian monk who lived in Brno in what is today the Czech Republic.

Mendel carried out breeding experiments with the garden pea, Pisum sativum, and is credited with being the "father" of the science of genetics - heredity.

Mendel did not know about chromosomes or DNA, nor did he know about genes as we do today.

Nevertheless, he performed many experiments in which he controlled the breeding of his pea plants.

By observing the number and types of phenotypes in the offspring plants he developed the rules of inheritance known as Mendel's laws today.

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stamenspistil

stigma

ovary

filament

petals

anther

Pisum sativumGarden peas: highly inbred with well-defined qualitative characteristics

Spherical seed (SS)

Wrinkly seed (ss)

x

SS ss

Ss....

SsSsSs

F1first filial

generation

Ss Ss

Ss Ss

S S

Parent 1

s

sPar

ent 1

Punnett Squareafter Reginald Punnett

1875-1967The World’s first Professor of Genetics

GametexSS ss

xSs Ss

S s

Parent 1

S

sPar

ent 1 Ss

Ss

SsSs

SS

SS

F2second filialgeneration

ss

ss

Homozygousdominant

Homozygousrecessive

Heterozygous

Phenotypes

SsSsSS ss

Genotypes

The Purity of Gametes, which is nowknown as the Law of Segregation

Alternative forms of a characteristic segregate in separate sex cells.

Alleles segregate in separategametes during meiosis

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Law of Independent Assortment: the alleles coding for one feature segregate separately from the alleles coding for another. We now know this is true only for alleles on separate chromosomes.

Variance is a measure of the dispersion of the scores around the mean. In fact, it is the mean of the squared deviations from the mean

Heritability

To understand heritability, we need to understand variance.

Variance =(scoren - mean)2

_________________number of scoresΣ

HeritabilityHeritability is the proportion of the variance in a particular characteristic amongst the members of a population that is due to genetics.

h2 =vgen

vgen + venvir_________ = vgen

vtotal_____

Heritability of intelligence, for example, isnot an estimate of how much genetics contributes to intelligence in an individual --but how much it contributes to differencesin intelligence between people.

What contributes more to the area of a desk top? The length of the desk or its width?

Consider the following sets of desksa

b

ab

Differences in the areas of the desktops in the top row are due to differences in dimension b

Differences in the areas of the desktops in the bottom row are due to differences in dimension a.

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NeoDarwinian Theory (natural selection coupled with Mendelian genetics) provided a remarkable framework for understanding how behaviour could evolve.

But even NeoDarwin approaches had difficulty explaining a number of different patterns of behaviour, including altruistic behaviour, where individual’s sacrificed themselves for others. How could that behaviour evolve?

What are the ultimate explanations for this behaviour?

Ultimate causes

Why are flamingos pink?

What’s wrong with the following argument?

“... the flamingo's pink legs are thought to be camouflage against the sunset when they are actually due to a diet of shrimps.”

from a letter to New Scientist Sept 25, 1999

Take the case of behaviour that can put an individual’s life at risk. What are the ultimate causes of that behaviour? How would that behaviour ever evolve?

KilldeerCharadrius vociferus

Some ground-nesting birds, such as the Killdeer, use a “broken-wing display” to lead a potential predator away from the nest.

Why would they put themselves at risk? What do they get out of doing this?

The answer is obvious of course.

They are helping to ensure that their young survive -- and since they share 50% of their genes in common with their offspring, this means that they are projecting their own genes into the next generation.

One can see how this behaviour would be selected.

Generationn

Generationn+1

XX X XX X

Genes for broken-wing display

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In other words, one can see how the behaviour will increase an individual’s fitness -- the success that the individual has in increasing its genetic representation in subsequent generations.

But not all behaviour will increaseindividual fitness.

Take the case of alarm calls -- whereby an animal warns others in the group, not just its offspring, about the approach of a predator.

If one imagines an animal, who by virtue of some mutation has a tendency to give an alarm call, wouldn’t that animal be more likely to be seen by the predator and eaten -- and thus wouldn’t that behaviour disappear from the population?

Golden-mantledground squirrel

Ground squirrels, for example, give alarm calls when they spot a predator. This will happen even when they don’t have offspring.

The other squirrels in the area then run for their burrows and hide.

Moreover, the ground squirrels who give alarm calls are often stalked and eaten by predators like owls and badgers.

This is the problem of altruism, behaviouralacts that may actually reduce an individual’s chance of survival and interfere with its own reproductive success.

Darwin himself was bothered by this problem.

But how could this kind of behaviour be selected?

The answer lies in the notion of kin selection.

In other words, genes that promote altruism within in individual could become more common in subsequent generations by increasing the survival and/or the reproductive capacity of relatives who share the same genes -- one’s kin.

J.B.S. Haldane, the great English biologist, one remarked,“I would gladly lay down my life for two brothers or eight cousins.”

1892-1964

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Inclusive fitness refers to the proportion of one’s genes that are projected into the next generation by all of the individuals with whom one shares those genes -- all of one’s kin.

Kin selection depends not simply on individual fitness, but on inclusive fitness.

Notice that this is a gene-centric explanation of natural selection and evolution. This new approach is sometimes called the Williams Revolution, after the American biologist George C. Williams.

b. 1926

The idea of kin selection can help explain some otherwise puzzling phenomena.

Consider the case of Belding’s Ground Squirrel.

Belding’sGround Squirrel

Female Belding’s Ground squirrels are three times more likely to give alarm calls than male Belding’s Ground Squirrels.

Why?

Kin selection helps explain why.

Females on average migrate 50 m from the burrow in which they were born.

Males on average migrate 400 m.

Male

Female

Thus, if a female gives an alarm call, she is much more likely to be warning a relative than a male would if he gives an alarm call.

Notice that kin selection does not require that the individuals know that they are warning their relatives.

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Some creatures such as bees, ants, and wasps are incredibly altruistic.

Worker honeybees, for example, do not reproduce -- but instead labour on behalf of the hive. They will sacrifice their life in defense of the hive.

Interestingly, the highly social insects like bees are almost all in the single Insect order, Hymenoptera

Hymenoptera have an interesting reproductive strategy called haplodiploidy.

The English biologist W.D. Hamilton showed how this strategy could account for the prevalence of altruistic behaviour in this order of Insects.

1936-2000

Females develop from fertilized (diploid) eggs while males develop from unfertilized (haploid) eggs.

1 2

3 4

Queen Drone

1. 50% 2. 100% 3. 75%4. 75%

Mean = 75%

1 2

3 4

Queen Drone

1. 50% 2. 50% 3. 100%4. 0%

Mean = 50%

25%25%50%

0%25%

Male’sgenes

Female’sgenes

Thus, female workers are more related to their sisters than to their own potential offspring: 75% vs. 50%.

Moreover, sisters are three times more related to each other than to their brothers: 75% vs. 25%.

In fact, brothers are two times more related to their sisters than their sisters are to them: 50% vs. 25%.

But there have been other explanations put forward to explain eusociality, ones that don’t depend on haplodiploidy.

The high degree of social behaviour and altruism that characterizes the social insects is sometimes calledEusociality.

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It has been argued that the emergence of eusociality depended on there being:

maternal carenest-building

but most importantly it depended on

the potential for heroic defence of a reproductive femalean abundant food supply that couldsupport a high concentration of individualsin one place.

Thus, given that a mother’s relatedness to her daughters is .5 and to her grand-daughters only .25, it might be in her interest to persuade her daughters to forsake reproduction and assist her in producing more offspring herself.

From the daughter’s point of view it makes little difference since she is on average as related to her sisters as she is to her own offspring.

Notice that this parental manipulationargument works for diploid as well as haplodiploid species.

It should work for some mammals as well.

Although it may be hard to believe, there are some mammals that appear to be eusocial.

Naked mole rat Heterocephalus glaber

Naked mole rat lives in colonies of 70 to 80 individuals.

They live underground in soil that is quite hard and impenetrable.

Tubers growing in soil provide “fortress of food” that can be defended.

One female, the queen, produces all the young and suckles them.

Two or three males are consorts. All the rest of the colony are either small workers who do the tunnelling, nest-building, and foraging or larger workers who do most of the defense.

Queen suppresses reproduction in other females by use of pheromones, probably in her urine.

Kin selection and parental manipulation, however, are not the only biological explanations for altruism.

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Reciprocal AltruismIs it possible for altruistic behaviour to occur among unrelated individuals?

The answer is yes.

Natural selection could favor altruistic acts between unrelated individuals if the individual performing the act at a reproductive cost to itself received repayment at a later time from the individual it helped. Robert Trivers

b. 1943

The idea is also captured in common phrases such as “You scratch my back and I’ll scratch yours!”

Reciprocal altruism is extremely common in human beings. Although it is far less common in other animals, it does occur.

In a sense, reciprocal altruism is like Aesop’s fable about Androclesand the Lion.

Take the case of the Baboons.

In some species, Male baboons will form alliances where one baboon will engage an alpha male in a fight while the other copulates with the alpha male’s female consort. On a later occasion they will reverse their roles.

There is a real risk for the individual who engages the alpha male in a fight.

Clearly then, there must be some payback later.

In other words, reciprocity must occur.

Reciprocal altruism will emerge more often in species where there is:

• Individual recognition

• Long-lived individuals

• Stable communities

• Well-developed memory

Kin selection and reciprocal altruism can reinforce one another.

Thus, altruistic behaviour is likely to be more common in small towns than in large urban centres.

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http://salmon.psy.plym.ac.uk/year3/PSY339EvolutionaryPsychologyroots/EvolutionaryPsychologyroots.htm

A great site for reviewing how Darwin contributed to modern psychological thought

http://www.amnh.org/exhibitions/darwin/

A wonderful account of Darwin’s life and thought.