Descent With Modification Darwin’s theory of evolution

Before Darwin… Aristotle’s scala naturae – scale of complexity He basically just rated everything on a scale of rock to God. He believed species were fixed.

Influences on Darwin Paleontology Geology Lamarck Malthus

Paleontology/ Geology Paleontology= Study of fossils (in case you didn’t know) Could roughly date by strata (rock layers) Older fossils were less similar to today’s life Take-aways for Darwin: - The Earth is super old (closer to 4.5 billion than 6000 years) - Slow processes over great time can also act on life.

Thomas Malthus Economist Hypothesized that much of human suffering was due to the population increasing faster than food supply or resources. More people are born than can survive

Lamarck Gets made fun of by evolutionary biologists (and not just because of the haircut) Compared fossil and modern species and noticed lines of descent. Older species changed to become modern species.

Lamarck’s Theory Use and disuse- – Body parts that are used become bigger and stronger. – This can be passed on to offspring

So we know he wasn’t right… Or was he? -First reasonable explanation of fossil record. -Maybe science can shed light on the forms of modern species. -Also epigenetics validates him to some extent. Well, mostly he was wrong, but he opened the door for new ideas.

Charles Darwin At age 16, Darwin was sent by his father to study medicine. He left and enrolled at Cambridge to become a clergyman. (A career that interestingly allowed him to pursue his interest in becoming a naturalist) At the age of 22, Darwin set out on a voyage on the HMS Beagle. I’m on a boat!

The Voyage The goal was to chart the South American coast. Darwin’s job was to collect and document the species he encountered.

The Galapagos Young volcanic islands west of South America Although geologically close, the islands each offered unique conditions and ecosystems. Darwin hypothesized that the organisms of the islands were descendants of colonizing species from the mainland that had changed over time.

Adaptation Characteristics of organisms that increase fitness. These can be inherited! Classic example  Finches

Natural Selection Observation 1: Members of a population have variation in their traits. Observation 2: Offspring inherit traits from their parents. Observation 3: All species are capable of producing more offspring than the environment can support. (Malthus) Observation 4: Many of these offspring are unable to survive

Therefore we can infer… 1.Individuals with traits that allow them to better survive and reproduce tend to leave more offspring than other individuals. 2.Traits that help organisms survive will become more frequent over generations.

The Origin of Species Darwin first wrote about natural selection in 1844, but put off publisihing In 1858 Alfred Russel Wallace sent Darwin a copy of his theory of natural selection- Darwin finally stopped procrastinating and published his theory. He got the credit because he wrote it first and because Wallace was cool about it. Wallace: the first hipster???

The Origin of Species Over the years, Darwin had collected overwhelming evidence and support for his theory: – Fossil record, artificial selection and so many examples! Darwin’s theory was accepted by most scientists within a decade.

Important Points 1.Although natural selection relies on the interactions of individuals with their environments, individuals do NOT evolve. Populations evolve. 2.Natural selection can only work on traits that are inherited (sorry Lamarck) 3.The environment varies over space and time. A trait that is favorable in one environment may not be helpful in another.