Evolution

What does it all mean?

What do you think?

• Do populations of organisms change over time?• Are there genetic differences between different

populations of the same species?• Are there organisms on earth now that weren’t here a

million years ago?• Are there organisms that were here a million years ago

that aren’t here now?• Are there some species that are very, very similar to

other species? • Do you believe that evolution is true?

Charles Darwin

• Studied medicine unsuccessfully.• Attempted to get a degree in theology.• Became the (untrained) naturalist aboard the Beagle.

• Developed the theory of natural selection.

Theories

• “Gravity” is a theory!• Atomic theory• Pythagorean theorem• Theory of Natural Selection• Theory of Evolution• A law explains one specific thing. A theory

explains a whole set of phenomena or events.

The Birth of Natural Selection

• Darwin supposed that genetic differences could lead to greater biological success.

• Those genetic differences that reduced biological success would have less of a chance of being passed along to the next generation.

• His radical thought was that this process could lead to the rise of new species.

Alfred Wallace

• Darwin waited years before publishing his theory.

• In that time, Alfred Wallace (a biogeographer) sent him an essay in which Wallace had arrived at the same conclusion Darwin did. Natural Selection drives evolution.

• When the theory was presented at a scientific meeting, it was not evolution that was fiercely debated…it was natural selection.

Evolution in a nutshell…

• “Life on earth evolved gradually beginning with one primitive species- perhaps a self-replicating molecule- that lived more than 3.5 billion years ago; it then branched out over time, throwing off many new and diverse species; and the mechanism for most (but not all) of evolutuionary change is natural selection.”

• From Why Evolution is True by Jerry Coyne

Components of Evolution

• Evolution• Gradualism• Speciation• Common ancestry• Natural selection

Evolution

• Species undergo genetic change over time• Changes in DNA originate as mutations• Some species of plants and animals around

today weren’t around in the past.• Some species evolve rapidly (humans). Some

evolve much more slowly (coelacanth).

Gradualism

• Evolutionary change takes many generations (hundreds, thousands, even millions)

• Microbes have very short generations (minutes), which accounts for drug resistance.

• Evolutionary pressure drives the rate of genetic change. Colonization of a new environment, for example, increases the rate of evolution.

Speciation

• If evolution only meant genetic change over time, we’d only have one highly adapted species.

• Speciation- evolution of different groups that cannot interbreed.

• Two populations of a single species begin to evolve slight differences based on the individual evolutionary pressure of their habitat.

• Not all species split into two. Some stay the same and others become extinct, leaving no ancestors.

Common Ancestry

• The flip side of speciation.• Every pair of species shares an ancestor. • The closer related two species are, the more

recently that common ancestor lived.• The further apart the species are genetically,

the longer ago their common ancestor lived.

Natural Selection

• Individuals of a population vary genetically from each other.

• Some of those differences affect an individual’s ability to reproduce and survive in its environment.

• In the next generation, there will be more of the “good” genes than the “not so good” genes.

Wooly Mammoth Example of Natural Selection

• Wooly mammoths have a thick layer of hair.• Probably decended from ancestors with little hair.• Some mammoths (like humans) are hairier than

others.• As the climate became colder, the hairier

mammoths tolerated their surroundings better than their counterparts.

• Survival of the fitter, not fittest.

If evolution is true, then…• We should be able to find evidence for evolutionary

change in the fossil record.• We should be able to find new species forming in the wild.• We should be able to find some evidence of “missing

links” (transitional forms) that link major groups with each other in fossils.

• We should expect that species show genetic variation for many traits.

• We should be able to find cases of imperfect adaptation.• We should see natural selection acting in the wild.

Fossils

• Previously thought to be the work of supernatural forces or remains of still-living species inhabiting remote parts of the globe.

• Have been written about since ancient times.• Requires a very specific set of circumstances in

which to form.

How a Fossil Forms

1. The remains of an organism must find its way into water, sink to the bottom and be quickly covered by sediment.

2. Most fossils are of marine organisms.3. Hard parts of fossils become replaced by minerals.4. Soft parts of plants and animals are rarely fossilized. 5. Over the first 80 percent of the history of life, all

species were soft bodied! 6. Most fossils will never be discovered.

Evidence for the Fossil Record

• Radiometric dating• Principal of superposition• DNA evidence