The Evolution of Living Things

Section 1: Change over Time

Section 2: How does Evolution Happen?

Section 3: Natural Selection in Action

Change Over Time Adaptation: a characteristic that helps an

organism survive and reproduce in its environment

Species: a group of organisms that can mate with one another to produce fertile offspring

Population: groups of individuals of the same species living in the same place

Evolution The process in which inherited

characteristics within a population change over generations such that new species sometimes arise

Fossils The remains or physical evidence of an

organism preserved by geological processes

Fossil record: a historical sequence of life indicated by fossils found in layers of the Earth’s crust

Evidence of Ancestry

Adapted from "A Simplified Family Tree of Life" in The Evidence of Evolution by Nicholas Hotton III, Smithsonian, c1968.

Geological Time Scale

Examining Organisms Evidence of Whale Evolution (p. 170, Fig. 7)

Pakicetus: Scientists think that whales evolved from land-dwelling mammals that could run on four legs; one of these ancestors may have been Pakicetus, which lived about 50 mya

Ambulocetus: This mammal lived in coastal waters about 49 mya; could swim by kicking its legs and using its tail for balance

Dorudon: This mammal lived in the oceans about 40 mya; resembled a giant dolphin with tiny hind limbs that could not be used for swimming or walking

Modern toothed whale: Forelimbs are flippers; no hind limbs, but do have tiny hip bones; range in size from 1.4 m porpoises to 33 m blue whales

Comparing Organisms Comparing Skeletal Structures: similarities

in arrangement of bones suggests that cats, dolphins, bats, and humans had a common ancestor

Comparing DNA: every organisms inherits the traits determined by DNA; if two species have similar DNA, the hypothesis suggesting common ancestry is supported

Charles Darwin (1809-1882) Took a five-year voyage around the world on the

HMS Beagle in an effort to study nature and to explain HOW evolution happens

Studied finches on the Galapagos islands

Thomas Malthus (1766-1834)"In October 1838, that is, fifteen months after I had begun my systematic inquiry, I happened to read for amusement Malthus

on Population, and being well prepared to appreciate the struggle for existence which everywhere goes on from long-

continued observation of the habits of animals and plants, it at once struck me that under these circumstances favourable

variations would tend to be preserved, and unfavourable ones to be destroyed. The results of this would be the formation of a new species. Here, then I had at last got a theory by which to

work".

Charles Darwin, from his autobiography. (1876)

Charles Darwin – Theory of Natural Selection As random genetic mutations occur within an

organism's genetic code, the beneficial mutations are preserved because they aid survival -- a process known as "natural selection." (Descent with Modification) These beneficial mutations are passed on to the next generation. Over time, beneficial mutations accumulate and the result is an entirely different organism (not just a variation of the original, but an entirely different creature).

In 1859, Darwin published his famous book, “On the Origin of Species by Means of Natural Selection”

Natural Selection in Action In 1930, about 99% of the male elephants

in one area had tusks; today, because of hunting for ivory, only 85% of the male elephants in that area have tusks

Insecticides – insects developing resistance Antibiotics – bacteria developing resistance Peppered moths – industrial melanism

Forming a New Species Speciation: the formation of new species

as a result of evolution Separation Adaptation Division

The Evolution of the Galapagos Finches Some finches left the mainland and reached one of the

islands (separation) The finches reproduced and adapted to the environment

(adaptation) Some finches flew to a second island (separation) The finches reproduced and adapted to the different

environment (adaptation) Some finches flew back to the first island but could no

longer interbreed with the finches there (division) This process may have occurred over and over again as

the finches flew to the other islands

Review When a single population evolves into two

populations that cannot interbreed anymore, __________________ has occurred.

speciation

Review Darwin’s theory of

______________explained the process by which organisms become well-adapted to their environment.

natural selection

Review A group of organisms that can mate with

each other to produce offspring is known as a(n) ________________________.species

Review The _____________provides information

about organisms that have lived in the past.fossil record

Review In ________________, humans select

organisms with desirable traits that will be passed from one generation to another.

selective breeding

Review A(n) _________________helps an

organism survive better in its environment.adaptation

Review Populations of insects and bacteria can

evolve quickly because they usually have a short ___________________________.generation time