Species, Change and Evolution From the beginning, people have sought to understand and explain the amazing diversity of living things found on Earth For example, how is it that there are more than 40,000 species of snails and slugs yet only about 7650 species of clams? How can a sand dollar be so different from a blue whale? At the same time, we wonder about the great similarity between some species, like horses and donkeys, people and gorillas.

The history of life: looking at the patterns The central ideas of evolution say that life has a history — it has changed over time — and that different species share common ancestors. http://www.nbii.gov/portal/server.pt?open=512&objID=404&&PageID=1617&mode=2&in_hi_userid=2&cached=true

But first...details to know What is DNA? What are genes? Your DNA is a kind of molecule that makes up genes in the cells of an organism. Your genes tell your body what traits to have. Genes are inherited from your biological parents, half from mother, half from father.

What is biological evolution? “A change in the genes of a species over time.” Evolution requires time and reproduction over multiple generations. A species can evolve, but individual organisms cannot. e.g., the human species can evolve over time. A single person cannot evolve over time, they can only acclimate to changes during their lifetime.

What is a species? A group of organisms that breed with one another in the wild and produce fertile offspring. The American Robin is a species; it only breeds with other American Robins. House cats and tigers are different species; though they may look alike, they do not breed with each other.

What about hybrids? When closely related species mate, they produce hybrids. Usually hybrids don’t survive or can’t mate. Example: donkey + horse = mule Sometimes they produce fertile, successful offspring. Examples: coyote-wolf-dog; grizzly bear and polar bear

Ligers, Tigons and Zonkeys http://www.pbs.org/wgbh/evolution/library/05/2/l_052_02.html

Hybrids with Magical Powers? Ligers, Tigons, Zonkeys, Mules, etc. are not species (review the definition of species) Liger has mane: male lion + female tiger (liger female fertile and male liger infertile) Tigon, the largest cat in world: male tiger + female lion Liger males are sterile, female ligers are fertile and can produce Ti-liger (tiger dad and liger mom)

So, how does evolution happen? One way is by the process of Natural Selection! Nature (the environment) “chooses” which individuals are selected out of a population and which individuals are selected to survive. These are called selection pressures. A disease is a negative selection pressure because it selects out those individuals who aren’t immune to it.

Four Important Principles for Natural Selection Overproduction: more babies than can survive Variation: lots of varieties are born, some are “fit,” some are “unfit” Adaptation: inherited traits that give offspring an advantage Selection: nature selects the most “fit” individuals of each generation All of these help make Natural Selection “work” in nature. *Biological fitness means “survive longer, be healthier, have more offspring”

An equation for evolution. Evolution = M + NS* + SS + I + T + D Natural Selection = OP + V + A + S

A Misconception: “Natural selection gives organisms what they ‘need This just isn’t true! Natural selection has no intentions or senses; it cannot sense what a species “needs.” A species can’t “get” the traits it needs in order to survive an environmental change.

“Survival of the Fittest” is part of Natural Selection. Survival of the fittest says… The most “fit” individuals in a species survive. The most fit have more babies and pass on their advantageous traits. Over time, more of the species are like the fit “survivors.” Nature produces a lot of “mistakes,” and these “mistakes” die. What kinds of traits would be bad? good?

Natural Selection Fancy Pants Definition Natural Selection: The process in nature by which only the organisms best adapted to their environment tend to survive and transmit their genetic traits (like the color of their fur, or the length of their fangs) to the next generation, while those less adapted tend to either not reproduce very much or to be eliminated, ie, killed. http://en.wikipedia.org/wiki/Natural_selection

Whose Idea Was Natural Selection? Charles Darwin, 1859, On the Origin of Species, established the idea that there is “descent with modification,” or change over time. Supported by an enormous amount of evidence. Can be used to predict observations and outcomes.

Evolution by natural selection is a scientific theory. Supported by an enormous body of evidence collected by many scientists. Observed in living and fossil organisms. Used to predict changes in organisms before they happen.

But “it’s just a theory!” Hypothesis: an untested statement or idea. Theory: well tested, appears to be true in all cases. Essentially, a fact. Theory of Gravity, Atomic Theory Theory of Evolution, Plate Tectonic Theory All of these are subject to further testing and modification, and later may even be replaced with another theory!

How to prove a theory false? Identify some other process that explains the same observations.

What can evolution do? Microevolution (small genetic changes in a species from one generation to the next). Changes in color, size, etc.; remains the same species Sometimes you can’t even see it Red and Yellow Shafted Flickers are the same species, but look slightly different

What can evolution do? Macroevolution (the evolution of new species from a common ancestor over many generations). Common primate ancestor evolves to several living and extinct types, like humans, chimps, gorillas, etc. Evolution helps us to understand the history of life.

Small-scale changes (microevo) and large-scale changes (macroevo). . . From a Common Ancestor From Species “A” Comes a slightly different Species “A” Comes a New Species