Charles Darwin & Natural Selection

LifelineLifeline n Born 1809 n Study (Edinburgh and Cambridge) n Voyage of the Beagle n Retired to Down 1842 n The Origin of Species 1859 n Died 1882 Darwin’s home at Down, near London

Darwin’s achievements n Transformed biological science  Both style and content  Still the cornerstone of biology  Now the cutting edge of psychology n Transformed attitudes of humanity to our place in the universe

Not just an evolutionist n Not even a biologist to start with n Collected beetles for fun n Studied geology more seriously n Considered himself a geologist throughout the Beagle voyage and for some time after n Famous for working out how coral atolls are formed

Natural selection n Developed theory in complete isolation n 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 n Not paid for 5 years on Beagle. n Actually, he had to pay! n Was lucky to get on  replaced someone who was shot in a duel  his father opposed him going n Mainly asked because of his class, to keep Captain Fitzroy company n It was the making of him

CHARLES DARWIN n Video: Who Was Charles Darwin?Who Was Charles Darwin?

Galapogos, 1835 n Portrayed as a “Eureka” experience. n Actually, was hugely homesick n Did not recognise significance until back in England,  Worked out theory much later.  First inkling of natural selection in n 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 n He knew about fossils n Collected many for extinct animals n Knew about Lyell’s theory of “evolution” of geology n Read Malthus (an economist) on population and competition for resources. n Video Clip Video Clip n His ideas developed steadily over 20 years Darwin’s sand walk at Down: a daily thoughtful stroll

Alfred Russel Wallace n Thought of natural selection independently n Wrote to Darwin n Darwin had been working on book n Published a “letter” jointly n It was Darwin who put in the hard yards collecting and documenting evidence to support theory

Natural Selection n Process of change in populations over many generations n Individuals with certain traits survive local environmental conditions n Pass on favourable alleles to offspring n Environment exerts ‘selective pressure’ n This has led to biodiversity

Assumptions of Natural Selection 1. Variation -All members of a species display a variety of characteristics in their appearance and behavior. -Many are inherited.

Assumptions of Natural Selection 2. Competition The number of offspring produced by individuals in a species exceeds the number of offspring that will survive to adulthood

Assumptions of Natural Selection 3. Fitness Some offspring, because of their differences, are better able to adapt to the conditions of the environment than others.

Assumptions of Natural Selection 4. Adaptation The better-adapted organisms pass on their characteristics to their offspring and, as a result, the population changes.

“Descent with Modification” n Darwin never used the word ‘evolution’ in his book On the Origin of Species n Used the term ‘descent with modification’ instead

Artificial Selection n Selective pressure exerted by humans on populations n Improve or modify particular desirable traits n Eg. Selective breeding in farm animals

Artificial Selection n In food crops  Wheat, corn, rice and veggies have all been selectively bred n Wild mustard plant has been modified to produce broccoli, Brussels sprouts, cabbage and cauliflower n Breed for nutritional value, as well as harvest yield and pest resistance

Designer Dogs n How many breeds of dogs are there now? n Examples: n What do you get when you cross a Yorkie and a Poodle? Yorkie-poo

Designer Dogs n What about a Pug and a Beagle? Puggle n Or a Bichon Frize and a Poodle? Bich-Poo

Consequences of Artificial Selection n In dogs: respiratory problems (bulldogs) and hip dysplasia (labs) n In crops: reduces genetic variation (monoculture)