Evolution Before DarwinSBI3U Biology

Charles Darwin, 1809 - 1882• British Naturalist• Developed ideas of

Natural Selection, Evolution

• Traveled the world on HMS Beagle

• Published: On the Origin of Species, Descent of Man, Voyage of the Beagle, & works on emotions, botany, domestication…

The Beagle Voyage, 1831 - 1836• Gave Darwin an extensive opportunity to observe

organisms & fossils virtually worldwide, and to formulate new theories from his own observations & works he read.

The Galapagos Islands• Possibly the most famous stop on the five year

voyage• Unique organisms challenged Darwin to think

about their origins…

Is Change Possible?• Before Darwin, most people

would’ve said no, whether from a scientific perspective or otherwise

• Erasmus Darwin (Charles’ grandfather) felt that species could change over time & even become extinct.

• He felt change could happen through will, and that it represented a ‘degeneration of forms’

Change is necessary!• Darwin enjoyed reading

about Geology, and was well-versed in the leading ideas of the time:

• Gradualism • Uniformitarianism• Catastrophism• New ideas were arising,

many fossils being discovered; the science of Stratigraphy comes to be.

Gradualism• Earth can only change

slowly• The uniform & constant

change of our planet can be a model for the change in species

• Fossils indicate species have changed, and some are extinct

UNIFORMITARIANISM• Geological change on

Earth has been constant & slow

• Processes of change & rate of change have stayed the same: erosion, earthquakes, etc.

• Earth must be much older and life must change on a changing planet, in order to survive.

Catastrophism• Change on Earth can be,

at times, fast: floods, volcanos…

• Local change can be much faster than global

• Global catastrophes possible?

• The strata of the Earth were formed with successive catastrophes

• Fossils = the victims of these catastrophes, whether large-scale or local.

If everyone’s changing, what makes you so Special!?

• Darwin knew that organisms showed enormous variety of adaptations in form & behaviour

• Some forms are lost to us, as evidenced by fossils; living species must have something good about them…

• Struggle for Existence & Survival

Variable Reproduction• Not all species reproduce

at the same rate, nor with the same fecundity (number of offspring)

• Something similar happens within a species, also.

• So this must mean not every individual can survive.

• There must be a struggle.

Survival of the Fittest• Thomas Malthus• If left unchecked,

populations tend to grow exponentially

• But, no single species is overrunning the Earth…

• Limited resources make a struggle for survival necessary

• Those who get the resources are most fit to survive.

• *His essay, ‘On principles of population’, upset Darwin, since he advocated controlling human population by not allowing social welfare programs!

Change must be Heritable!• Change in an individual is

only useful if it can be passed on to offspring & future generations

• Several ideas existed for this, none of which were correct.

• This problem daunted Darwin

• All he had to work with were his own faulty theories, and…

• The Theory of Acquired Characteristics

Acquired Characteristics• Jean Baptiste de LaMarck• ‘Use or Disuse’ determined

which traits would become prominent

• Change could come by want or perceived need (‘I think I can, I think I can….’)

• Giraffes got their necks by stretching & trying really hard… Not quite!

Putting it All Together:• Variation within a species is heritable• Organisms tend to produce more

offspring than can survive, given limited resources

• A struggle to exist ensues, with not all offspring surviving long enough to reproduce

• Those individuals with traits adaptive or favourable to a given environment will survive long enough to pass on those traits; this is Natural Selection

• Over long periods of time, many small gradual changes lead to big changes in the traits of a species; this is Evolution – descent, with change.