mechanisms of evolution

MECHANISMS OF EVOLUTION

BACKGROUND TERMS Members of

the same species:

1. Can reproduce in a natural setting

2. and produce fertile offspring

APPLY SPECIES DEFINITION A horse and donkey can mate

in the barnyard to produce a mule.

The mule is a very strong, hardworking animal (albeit stubborn!), but alas,

mules cannot have babies. Are horses and donkeys

members of the same species?

No – the mule cannot reproduce, therefore is not fertile.

MORE SPECIES DEFINED

Are all birds members of the same species?

Think of the biggest and smallest birds you can imagine.

Certainly hummingbirds cannot mate with ostriches!

MORE SPECIES DEFINED

Are all domesticated dogs members of one species?

Can all dogs mate (theoretically)? Are all normal puppies fertile? Yes. All dogs are members of one

species: Canis domesticus

MORE SPECIES DEFINED A lion and tiger can

be artificially mated together in a zoo.

This produces a “liger”

Are lions and tigers therefore members of the same species?

No, they didn’t mate in a natural setting – and never would – they don’t even live on the same continent!

EVOLUTION VOCABULARY Branching diagram (CLADOGRAM) Shows changes in species over time Each new branch represents a newly

evolved feature

CLADOGRAMS

Which organisms have jaws? Which organisms have claws or nails? Is the salamander more closely related

to the perch or pigeon?

MORE CLADOGRAMSWhere in the image is now? Left, right, top or bottom?

CLADOGRAM SHOWING FISH EVOLUTION

Where is the common ancestor?

CLADOGRAM OF DINOSAURS

If a line stops before the top, what does that mean?

CLADOGRAM SHOWING EVOLUTION OF BIRDS FROM DINOSAURS

What is the common ancestor?

MORE CLADOGRAMS - SIDEWAYS

Where is NOW in these diagrams?

MECHANISMS OF EVOLUTION - VOCABULARY

Evolution: changes in species over time Speciation: the formation of new species Gradualism: the theory that species changed

very gradually over time. Fossil evidence shows jumps, but the hypothesis is that we simply haven’t found the in-between fossils (missing links).

Punctuated equilibrium: The theory that species are relatively unchanged for long periods, but then go through sudden rapid changes and new speciation, usually due to geographic isolation or environmental pressures.

EVOLUTION - VOCABULARY

Gradualism vs. punctuated equilibrium


Natural selection: (aka Survival of the Fittest) The members of the species that are best

adapted to the environment will survive to pass their genes on to the next generation.

The less well adapted will be more likely to die before reproducing, reducing the proportion of their particular set of alleles in their population.

The “environment selects” which members survive.


Fittest doesn’t necessarily mean strongest or fastest Competition is not usually direct Fittest = best adapted Adaptations:

Camouflage Mimicry Structure

• Different Teeth shapes for different foods• Beak shapes (as in lab)• Leaf color• Seed dispersal• Attractiveness for mate• Attractiveness for pollinators• Ability to withstand a freeze, or draught, or flood or …..

Can you come up with some?

EXAMPLES OF NATURAL SELECTION

During an especially cold winter, the birds with the most under-feathers (down) are more likely to survive, while some the others will die off. The “environment selects” the survivors, who then pass on their genes to the next generation.

EXAMPLES OF NATURAL SELECTION

Slower sea turtles may be eaten by gulls before fast ones, when trying to get to the ocean. The fast ones pass their genes on to produce fast offspring.

MECHANISMS OF EVOLUTION –GENETIC VARIATIONS

A strong species is one in which there are many differences, or variations, between individuals in the population.

These variations allow individuals to survive changes in the environment, and multiple situations.

Not all members survive, but the species does.

MECHANISMS OF EVOLUTION – VARIATIONS EXAMPLES:

Ex: The faster turtles on land may attract more attention from gulls, and may also be slower swimmers. Slow, better camouflaged ones may swim better and have higher chance of survival from predators once in the water. Both variations are important to the species.


Not all members of a population are susceptible to the same illnesses, or they would all die from the same disease.

Clones, which have identical genes, are all strong in the same areas and weak in the same areas. One event (drastic environmental change, new germ, loss of particular food source) could kill them all at once.


Irish potato famine in 1843. Due to LACK of variation Cloned potatoes all succumbed

to one single fungus species, that wiped out the whole potato crop for two years, starving 1 million.

MECHANISMS - OVERPRODUCTION

Many species purposely produce more offspring than they know will survive

This introduces competition, so that only the members with the best

adaptations survive and the less well adapted die off.

The less adapted may have survived if they didn’t have to compete with so many others

OVERPRODUCTION EXAMPLES

Frogeggs


Maple seeds

EVOLUTION IN ACTION: ANTIBIOTIC RESISTANCE

Antibiotics kill bacteria Bacteria usually reproduce by binary

fission, which is basically mitosis => genetically identical offspring But when the species is threatened, (as

when their environment changes with antibiotics) they can swap DNA through a conjugal bridge.


When bacteria conjugate, this introduces genetic variation, and gives the species a chance to develop a variation that does not get killed by the antibiotics


So if you don’t finish all your antibiotics, the strongest few could be left behind to multiply.

Then if you get sick again, you will need a different, stronger antibiotic to kill the stronger bacteria.

The bacteria have evolved, by natural selection, to survive the environmental pressures in your body


New species of bacteria evolve every day

Forcing the medical profession to constantly have to continue to develop new drugs to kill them

This “arms race” has led to “super-bugs”

such as a new strain of TB that is killing thousands and cannot be treated with antibiotics.

EVOLUTION IN ACTION: PESTICIDE RESISTANCE

The few insects of a species that survive reproduce, passing the survival genes down

Eventually, most of the population is unaffected by the pesticide

so that the pesticide eventually is rendered useless,

and the insect population is even stronger.

The arms race continues

EVIDENCE FOR EVOLUTION

Fossils

EVIDENCEcoprolite

Dino tracks - Utah

Mosquito in amber


Homologous structures


Analogous structures

EVIDENCE

Goose bumps

Vestigial structures – no longer needed

Snake pelvic bones

Whale pelvic bones

EVIDENCE

Embryonic comparison

EVIDENCE Biochemical comparisons

The more similar the DNA, the more recently two species branched apart.

Many other chemical processes are similar among species.

Soft tissue found inside fossilized dinosaur bones was found to have strikingly similar protein structures as those in chickens!

Can you see it?

OVERVIEW OF EVOLUTION

Earth formation 4.6 BYA Swirling ball of hot molten lava Gravity pulls in heavy solid nickel core Magma begins to cool into thin crust Rain begins to fall Harsh, hot, toxic, anaerobic (no free

oxygen in atmosphere)

FIRST 4 BILLION YEARS First life: archaebacteria –

prokaryotes Don’t need oxygen Don’t produce oxygen thrive in harsh environments like deep ocean vents &

hot caustic puddles at Yellowstone Next life: photosynthesizing prokaryotes

Cyanobacteria Make oxygen – for a billion years

Finally: single-celled eukaryotes (have nucleus and membrane-bound organelles) Endosymbiont theory = photosynthesizing prokaryotes

were absorbed by other bacteria to become the first organelles - chloroplasts

FIRST 4 BILLION YEARS

Soft-bodied Multi-celled eukaryotes Began as colonies of single-celled

organisms. Cells started to specialize and organize

into multicellular organisms No backbone yet

• jelly fish, • sponges, • Worms• seaweed

NEXT .5 BILLION YEARS (ABOUT 500 MY) Adaptive radiation: rapid speciation

due to new opportunities Once life organized, and the planet was

a comfortable living space, evolution happened in leaps and bounds,

with new species diverging, rapidly filling every niche

Cambrian explosion

EVOLVE HOW? Mutations

Some good, improve survival, so get passed down

Mixing of genes through sexual reproduction

Genetic “drift” (as in lab) Driven by Natural Selection Punctuated equilibrium Gradualism Adaptive radiation Remember…it took billions of years to get

this way!

EVOLUTION OF EVOLUTIONARY THEORY

Spontaneous generation – living things can arise from non-living things Based on pure observation Flies come from meat Bacteria comes from broth Frogs comes from rain!

EVOLUTION OF EVOLUTIONARY THEORY Biogenesis – living things come from

living things Break down the term

• Bio = life• Gen = birth, origin

Francesco Redi 1668• Disproved spontaneous generation by setting

up simple experiment to show covered meat produces no flies

EVOLUTION OF EVOLUTIONARY THEORY Jean-Baptiste Lamarck – theory of natural

selection: Organisms can change their genes through

their behavior Charles Darwin - theory of natural

selection HMS Beagle – voyage to Galapagos Islands 1830’s Helped form ideas of speciation by geographic

isolation from observations of species on mainland verses different islands

mechanisms of evolution

Documents

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