EvolutionEvolutionandand

DarwinDarwin

Evolution : what does it mean?

• Evolution : change over time

• Biodiversity : observation of similar or different structures or functions in animals and vegetables

CHARLES DARWIN1809-18821831 : He begun his

five- year sailing on the “Beagle “in the south seas(South America, Galapagos, ecc)

1859 He wrote : “On the Origin of Species by Means of Natural Selection”

History of evolutionary thought

Which theories… before Darwin ?

ANASSIMANDRO

ARISTOTELE

LECLERC DE BUFFON

JAMES HUTTON

CUVIER

LINNEO

LAMARK

ANASSIMANDRO(610-546 B.C.)

• “homo” comes from animals of different species as he cannot provide food himselfuntil he has grown up

ARISTOTLE (384-322 B.C.)

• The great chain of being(Latin: scala naturae )

• Hierarchical structure of all matter and life.

• Everything was supposed to be created by God

Creationism

• Religious belief that comes from the creation narrative of the Genesis

• Since then to nowadays nothing has changed

Carl Von Linnè (1707-1778)

• Fixity of species

CATASTROPHISM

• Earth has been affected in the past by sudden, short-lived, violent events (worldwide)

CUVIER (1769-1832)

• Many of the geological features of the earth

and the past history of life could be explained

by catastrophic events that caused the

extinction of several species of animals (fossils)

George BUFFON (1707-1788)

• l'Histoire naturelle, générale et particulière

• He was the first who tried to explain life variability

Erasmus DARWIN (1731-1802)the grandfather

• Animals are subject to changes whenever the environment gets modified. Descendants will receive changes as a heritage

• Great influence on his nephew

The Study of Geology was important to develop modern evolutionary theories

James HUTTON (1726-1797)actualism

• Great importance of timeline in geological changes (key role)

• Changes are slow• Earth is thousands of

years old

William SMITH (1769-1839)

• He discovered guide fossils

JEAN BAPTIST LAMARK (1744-1829)

• First scientist to propose an evolutionary theory– Evolution and

progression (giraffe necks)

– Acquired characters heritage

Trip on the south seas(1831-1836)

DARWIN

MALTHUS

economy

Charles LYELL

(1797-1875)

geology

Artificial

selectionGalapagos

Investigations

MALTHUS (1766-1834)• Population growth

(esponential)• Limit of resources

(linear growth)• Result: crisis• Solution: to stop the

growth (epidemies, death, disaster, ecc)

Charles LYELL (1797-1875)

• “Past is the key to get the present”He wrote “Principles of Geology”.According to him, the earth was shaped by slow-moving forces which are still in operation today. Lyell was a close and influential friend of Charles Darwin.

Artificial selection• Darwin considered how able the farmers and the

gardeners were in getting several minor variations among subjetcs belonging to the same species

• They used to select the useful features by artificial selection– Close relation between the artificial selection and the

natural one, although the natural one is considerablymore perfect and slower.

Breeds of domestic dogs obtained by artificial selection along 10.000 years

The beagle

Darwin analyzed different kinds of animal and vegetable samples -collected during sailing -and he observed similiarites between fossils and living species coming from the same area

Darwin observed that each

island of Galapagos

archipelago has got specific

kinds of turtles and birds

which are – at the same

time - similar and different

(aspects, diet….)

Galapagos observations• 14 Vulcanic islands

(Ecuador)• In the islands there are

several species both animal and vegetable due to isolation – large distance from

mainland – wide climatic and habitat

variations• “Endemic” - typical - species

While visiting the Galapagos Islands, Darwin made several remarkable discoveries.

The armadillo

The Glyptodonts

….are they relatives?????

• Similarity between the carapace of a giant fossil and smaller “shell” that covered living armadillos

• The armadillos are native to the Americas.Fossil "related" forms giant extinct, replaced, in the modern fauna, from the smallest species in the same basic group.

the grandchildren look like their grandparents

Fossils testify a relationship

• Darwin uses the branching structure of a tree.

• “The affinities of all the beings of the same class have sometimes been represented by a great tree...As buds give rise by growth to fresh buds, and these, if vigorous, branch out and overtop on all sides many a feebler branch, so by generation I believe it has been with the great Tree of Life, which fills with its dead and broken branches the crust of the earth, and covers the surface with its ever branching and beautiful ramifications."

«the grandchildren look like their grandparents“I think …..”

phylogenetic tree

Phylogenesis = evolution historyTHE TREE MAKES THE RELATIONSHIP BETWEEN THE DIFFERENT SPECIES

High level= living speciesLow level = ancient speciesFork = birth of new species

Birth of new species

• Two populations of the same species, which have been separated by a geographic barrier, differ very much in characters, so that they keep isolated in terms of reproductivity.

• The split populations over time may distinctly evolve different characteristics. If the geographical barriers are eventually removed, members of the two populations may be unable to mate each other successfully : the genetically isolated groups have emerged as different species

Adaptive radiation: is a consequence of allopatric speciation among island populations

• QUICK BIRTH OF NEW SPECIES

• e.g. mammalian 65 billions years ago (mass extinction )

• e.g. finches of Galapagos

• On islands, Darwin met several species of finches that - although being biologically related - displayed a variety of different features.

• Some of them were marked by larger beaks, while some other presented more brightly coloured tails.

• Darwin stated that those features were “adaptive,” meaning that over time the finches had genetically adapted to suit environment; he named that process as “natural selection.”

Finches of Galapagos

Natural selection can lead to formation of new species

• Patterns of evolution– Adaptive radiation : many related species evolved

from a single ancestral species. Adaptive radiation most commonly occurs when a species of organism successfully invades an isolated region, where a few competing species already exist. If new habitats get available, new species will evolve.

Adaptive radiation is an example of divergent evolution.• Divergent evolution : two or more related species

becoming more and more dissimilar (different environments)• Convergent evolution : unrelated species become more

and more similar in appearance as they adapt to the same kind of environment

Consequently …divergent evolution• Remarkable variety of forms : common ancestor.• As they adapted to different environments, the appearance of the

species diverged.

Convergent evolution

• Different species adopt similar solutions of evolution (either morphological, or physiological) in response to similar environmental conditions

• e.g.: fish, cetaceans , ichthyosaurs

NATURAL SELECTION

• ENVIRONMENT TO FIX POPULATION SIZE CONTROL• “Struggle for existence”• WHO IS MORE SUITABLE? Individuals in possession of

suitable traits to struggle for local resources, will be more contributing offspring to the next generation.

FITNESS = reproductive efficiency

Natural selection is the force acting in nature, to promote the survival of some individuals with certain variants of charactersAdaptation is the result of the selection of variants that accidentally are more favorable

Adaptation to abyssal environment

• Large mouth• Photophores:

structures suitable for light generation

( bioluminescence)

Angraecum sesquipedale - also called

Darwin's orchid - is an orchid of the

Madagascar.

In 1822 it is noteworthy for its long

spur and Charles Darwin suggested

that the flower was pollinated (by a

lately discovered moth) by a proboscis

whose length was then unprecedented.

His prediction had gone unverified for

21 years (after his death), when the

moth was discovered – so his hypotesis

found a confirmation.

BISTON BETULARIA… and industrial revolution

Originally, the vast majority of peppered moths had light colouration, which effectively camouflaged them against the light-coloured trees and lichens which they rested upon.

However, because of widespread pollution during the Industrial Revolution in England, many of the lichens died out, and the trees that peppered moths rested on became blackened by soot, causing most of the light-coloured moths, or typical, to die off from predation.

At the same time, the dark-coloured, or melanic, moths, carbonaria, flourished because of their ability to hide on the darkened trees.

Darwin Theory Summary

1. Species (populations of interbreeding organisms) change over time and places.

2. All organisms share common ancestors with other

ones

3. Evolutionary change is gradual and slow

The primary mechanism of change over time is natural selection

The Process of Natural Selection

Darwin’s process of natural selection is made of four components.

1. Variation . Organisms (within populations) show individual variation in appearance and behaviour.

2. Inheritance . Some traits are consistently passed on from parent to offspring.

3. High rate of population growth . Most populations have more offspring - each year – compared to local resources, leading to a struggle for resources. Each generation experiences substantial mortality.

4. Differential survival and reproduction . Individuals possessing traits - well suited for struggling on local resources - will more contribute to next offspring

• During the twentieth century, genetics studies were fully integrated with Darwin’s mechanism, allowing us to consider the natural selection as the differential survival of genotypes, corresponding to particular phenotypes.

• Natural selection can only work on existing variations within a population.

• Such variations arise by mutation, i.e. change in some part of the genetic code for a trait.