Evolution I

There is grandeur in this view of life…C. Darwin, On the Origin of Species

1859

The Evolution of an Idea

“would it be too bold to imagine, that all warm-blooded animals have arisen from one living filament, which THE GREAT FIRST CAUSE endued with animality”E.Darwin, Zoonomia vol 3 1794

Erasmus Darwin painted by Joseph Wright of Darby

Lamarck: Transmutation of Species

Jean-Baptiste Lamarck

Life becomes more complex over time

Adaption occurs via use and disuse

Changes to an individual during its lifetime are inherited by its offspring

Natural Theology

Most people thought that all species had been created independently and had fixed forms

The living world was thought to have been created by a benevolent god giving each species a specific function in the natural world

Study of the natural world was thought to illuminate god’s creation and benevolance

Parasitic Wasps : Benevolence in action?

A Clergyman in the Making?

Charles Darwin

Born 1809 to a wealthy doctors family

Studied Medicine at Edinburgh before transferring to Cambridge to take a bachelors degree At Cambridge he became interested in geology and natural historyAfter graduation he had to wait a few years before he could be ordained into the church

Ice ages in Wales

Cwm Idwal and the Ogwen Valley. A classic post glacial landscape

In the summer of 1831 he travelled through wales with the geologist Adam Sedgwick becoming convinced of the gradual origin of the landscape

Robert Fitzroy

Vice-Admiral Robert Fitzroy RN.

From an aristocratic Family (Uncle was Lord Castlereagh)

Master and Commander of HMS Beagle in 1831

Went on to become the second governor of New Zeeland in the 1840’s

Was a skilled geographer and survayor

Developed the science of metrology and published the first weather forecasts

Fitzroy’s OfferFitzroy was given command of HMS Beagle to complete the survey of the South American coast started some years before

He was worried that the length and distance from home would take its toll on his mental health and wanted a social companion

He was looking for a gentleman geologist/naturalist who could pay his own expenses to take part in the voyage

Darwin’s tutor at Cambridge suggested him and his uncle Joseph Wedgewood persuaded his father to let him go

The Voyage of HMS Beagle

Dec 1831 to Oct 1836

The Galapagos Islands

Giant Tortoises

San Cristobel North Isablea South Isablea

Darwin’s Finches

Coral Islands

Return to EnglandOn his return to England Darwin settled to analyzing his notes and specimens with the help of others in particular Sedgwick, Robert Owen and John Gould

Gould identified the birds collected in the Galapagos as finches not the mixture of families Darwin had identified

Fossils collected in Patagonia were identified by Owen as extinct mega-fauna

He married his cousin Emma Wedgwood and Settled in Gower Street, London before moving to Down House in Kent.

Malthus: An Essay on the Principle of Population

Population

Food Supply

Reverend Thomas Malthus

Pigeon Fancying Racing Homer Frillback

English PouterFantail

Artificial Selection The fancy pigeons like breeds of dog and farm animals and plants are breed to give desired characteristics

Individuals showing the wanted feature well and few unwanted features are crossed

In the next generation the offspring showing the wanted features best are again crossed

Over time the wanted feature (fan like tail, large crop, speed) will increase and the breed changes form

The Struggle for ExistenceTo keep the numbers of a population stable each adult pair needs to raise 2 offspring to adulthood in their lifetime

Each breeding pair actually produces many more offspring than this yet population numbers remain more or less stable

Most of the offspring die of starvation, disease or predation before they reach maturity

Only a small number survive and breed in their own turn

Natural SelectionAll individuals show some variation from the species norm

Most individuals die before reaching adulthood

Those showing most adaptation to the environment are most likely to survive and breed

Over time the species will change to become more adapted to the environment

So if the environment changes the species change to make its self more suited to the new conditions

Adaptive Radiation

Blistering BarnaclesDarwin wanted to write a description of all barnacle species living and extinct in the world

After 10 years of work he finished a description of all the barnacles living in the waters of Great Britain and some of the more important fossil species

Alfred Russell Wallace

Born 1823 to a relatively poor family

Worked as a surveyor in the 1840’s before becoming a professional naturalist

Travelled widely in South America and the Malay Archipelago

Became an expert on the geographical distribution of animals as well as evolution

Animal Collecting

Wallace made his living by collecting animal specimens for sale to collectors

From 1848 to 1852 he travelled in the Amazon Basin collecting animals but lost most of his specimens when his homeward bound ship sank

From 1854 to 1862 he undertook a second expedition to the east indies (Malaysia and Indonesia)

The Wallace Line In the North West the fauna is Asian e.g. tigers, elephants and orang-outangs

To the south west it is Australian eg marsupials.

Change of Forms Published “On the Law which has Regulated the Introduction of New Species” in 1855

This outlined some work on distribution of species and suggested new species arose close to existing ones

In 1857 or 1858 during a bout of Malaria in the Borneo jungle Wallace re-read Malthus and developed a theory of natural selection

Wallace’s Letter

“if Wallace had my MS. sketch written out in 1842, he could not have made a better short abstract! Even his terms now stand as heads of my chapters. Please return me the MS., which he does not say he wishes me to publish, but I shall, of course, at once write and offer to send to any journal.”Charles Darwin in a letter to Charles Lyell

In early 1858 Wallace wrote to Darwin proposing a mechanism for the emergence of new species and asked for Darwin’s comments

Two papers one by Wallace and one by Darwin were read to the Linnaean Society in July 1858 with an introduction by Lyell and Huxley

On the Origin of Species by Natural Selection

Darwin wrote the Origin between July1858 and March as a “short” abstract of his ideas

1250 copies of the first edition were sold on or before the day of publication, the 3000 copy second edition was sold out before the end of January 1860

The book describes artificial and natural selection and some of the main lines of evidence Darwin had for developing the theory

What is a Species?A species is a group of individuals with a common form and life style

Each species occupies an ecological niche

Individuals of a species can breed with other individuals of the same species and produce fertile offspring

A species is a population of individuals that can and do interbreed with each other

Populations that stop interbreeding can become separate species

Natural Selection

Only individuals well adapted to the environment survive

Only traits carried by surviving individuals are present in the next generation

Over time individuals become more adapted to their environment and change form to become new species

Common Descent

All living things descend from previous living species

As time passes species change into one other forms

All living things come from 1 single common ancestor and this form has been altered by variation and natural selection to give the adapted forms we see around us

It is this common descent that has given rise to the common features that make classification possible

There is no progress in evolution only change

The Age of the Earth

Landscapes are formed by constant simple geological processes going on today

These include sedimentation, erosion, volcanism and earthquakes

While climate and events may change the processes do not

To form the structures in the landscape takes time and so the earth is 100’s of millions of years old at least (actually around 4.5 billion years old)

The Fossil Record

Structural Homology

Embryology

Human

Dog Cat

Darwin Photo

Evolution of the Eye

A Sequence of intermediate forms leading to the structure of the eye

Each form can be found in different extant species

FitnessFitness is a measure of how well an individual is adapted to its environment

This has nothing to do with “strength” but is measured by reproductive success and survival

The longer you live and the more children, nieces and nephews the greater your fitness to the environment

The Oxford Debate: Survival of the Fittest

Samuel Wilberforce, Bishop of Oxford

Thomas Henry Huxley

The Descent of Man“light will be thrown on the origin of man and his history” C. Darwin, Origin of Species 1859

Sexual SelectionAn Individual that survives 2 years and has 10 offspring is “fitter” than one that survives 10 years and has 2 offspring

As well as competing for resources individuals also compete for mates

Males can evolve a feature solely because females find it attractive and visa versa

The Problem of Inheritance If natural selection is to produce evolution variation must be inherited

Also a small amount of variation must be able to spread through a population

An even mixing of characteristics will lead to variation being “averaged out” of a population not retained

Neo-DarwinismThe combination of mendelian population genetics with natural selection is known as the “neo-Darwinian synthesis”

This combination is the main current theory of evolution and we will look at these ideas and the evidence for them in the next lecture