Charles Darwin & Natural Selection

Lifeline Born 1809 Study (Edinburgh and Cambridge)

1825-1831 Voyage of the Beagle 1831-36 Retired to Down 1842 The Origin of Species

1859 Died 1882

Darwin’s home at Down, near London

Darwin’s achievements Transformed biological science

¨ Both style and content¨ Still the cornerstone of biology ¨ Now the cutting edge of psychology

Transformed attitudes of humanity to our place in the universe

Not just an evolutionist Not even a biologist to start with Collected beetles for fun Studied geology more seriously Considered himself a geologist

throughout the Beagle voyage and for some time after

Famous for working out how coral atolls are formed

Natural selection Developed theory in complete isolation In face of violent (religious) opposition

¨ With no knowledge of genetics¨ With no knowledge of DNA¨ With no knowledge of plate tectonics ¨ With no observations of natural selection

actually occurring

Joining the Beagle Voyage Not paid for 5 years on Beagle. Actually, he had to pay! Was lucky to get on

¨ replaced someone who was shot in a duel

¨ his father opposed him going Mainly asked because of his class, to

keep Captain Fitzroy company It was the making of him

CHARLES DARWIN Video: Who Was Charles Darwin?

Galapogos, 1835 Portrayed as a “Eureka” experience. Actually, was hugely homesick Did not recognise significance until

back in England, 1837.¨ Worked out theory much later.¨ First inkling of natural selection in 1838.

Turtles & finches were key evidence¨ On boat home, ate turtles, dumped shells¨ Thought finches different species; didn’t

even label them properly

The Big Idea: Natural Selection

He knew about fossils Collected many for extinct animals Knew about Lyell’s theory of “evolution” of

geology Read Malthus (an economist) on population

and competition for resources. Video Clip His ideas developed steadily over 20 years

Darwin’s sand walk at Down: a daily thoughtful stroll

Alfred Russel Wallace Thought of natural selection

independently Wrote to Darwin Darwin had been working on book Published a “letter” jointly It was Darwin who put in the hard

yards collecting and documenting evidence to support theory

Natural Selection Process of change in populations over

many generations Individuals with certain traits survive

local environmental conditions Pass on favourable alleles to offspring Environment exerts ‘selective pressure’ This has led to biodiversity

Assumptions of Natural Selection1. Variation

-All members of a species display a variety of characteristics in their appearance and behavior. -Many are inherited.

Assumptions of Natural Selection2. Competition

The number of offspring produced by individuals in a species exceeds the number of offspring that will survive to adulthood

Assumptions of Natural Selection3. Fitness

Some offspring, because of their differences, are better able to adapt to the conditions of the environment than others.

Assumptions of Natural Selection4. Adaptation

The better-adapted organisms pass on their characteristics to their offspring and, as a result, the population changes.

“Descent with Modification” Darwin never used

the word ‘evolution’ in his book On the Origin of Species

Used the term ‘descent with modification’ instead

Artificial Selection Selective pressure

exerted by humans on populations

Improve or modify particular desirable traits

Eg. Selective breeding in farm animals

Artificial Selection In food crops

¨ Wheat, corn, rice and veggies have all been selectively bred

Wild mustard plant has been modified to produce broccoli, Brussels sprouts, cabbage and cauliflower

Breed for nutritional value, as well as harvest yield and pest resistance

Designer Dogs How many breeds

of dogs are there now?

Examples: What do you get

when you cross a Yorkie and a Poodle?

Yorkie-poo

Designer Dogs What about a Pug

and a Beagle?

Puggle Or a Bichon Frize

and a Poodle?

Bich-Poo

Consequences of Artificial Selection

In dogs: respiratory problems (bulldogs) and hip dysplasia (labs)

In crops: reduces genetic variation (monoculture)