Lecture 10: Basics of Evolution

Covers Chapter 14 & 15

• Did you ever wonder why ostriches have wings when they cannot fly?

• Answer: Ostriches EVOLVED from other birds that can fly.

• Ostriches share a COMMON ANCESTOR that could fly, but then they evolved into birds that cannot fly.

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Evolution of Rhino

Evolution

• We have all heard of Charles Darwin, who is named the Father of Evolution.

• Before Darwin, however, science was heavily influenced by religion.

• God created the world and all organisms in the world and nothing has changed since then.

• In the 1700’s things began to change.

Evolution

• Europeans began to explore the earth: Asia, Africa, etc.

• They began to notice that there were many more species, or types of organisms, than anyone ever thought.

• Patterns began to emerge: – Each geographic area has its own unique species– Scientists began to think that perhaps organisms

changed or evolved to live in their unique habitat– Perhaps species weren’t fixed, they changed…..

Evolution

• Next was the discovery of fossils: preserved remains of organisms that died long ago.

• As people began building roads and more modern buildings, they began to dig up rocks that looked like bugs, birds, and other animals.

• Scientists began to understand that fossils were buried in different layers of the earth, and these layers corresponded to how long ago the organisms lived and died.

• Fossil remains also revealed that fossils from shallow layers in the earth resembled modern organisms more so than those fossils in deeper layers and those fossils in deeper layers were of simple, less complex organisms and often represented species that were no longer alive in the present.

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(a) Trilobite (b) Seed ferns (c) Allosaurus

Youngestrocks

Oldestrocks

How do we know the age of fossils?

• Radiometric dating: Utube

• Fossils are constantly being discovered

• Fossils have been found that are 3.5 billion-4.5 billion years old.

Stromatolites

Evolution

• Next up was the proposal that the Earth’s present landscape was produced by past action of things like volcanoes, flooding rivers, movement of tectonic plates under the ground, etc. This led to the belief that the Earth was very old.

• Modern geologists estimate that the Earth is 4.5 billion years old.

The Evolution of Evolutionary Thought!

• Lamarck, 1800’s: younger fossils are more complex than older ones, so perhaps species are changing and becoming more complex over time AND PERHAPS these more complex organisms INHERITED their complexity from their parents.

• Later in the 1800’s Darwin and Wallace began the real work on evolutionary thought.

Darwin & Wallace

• Both traveled extensively and studied plants and animals.

• Both observed that there was an increasing complexity in the fossil record.

• Both observed that some organisms that may not be related nevertheless had similar features.

• Both suggested that ORGANISMS CHANGE OVER TIME.

Darwin’s Finches

Fig. 14-5

Darwin & Wallace

• Both wrote papers about this new theory.

• Descent with modification: individual organisms in each generation differ slightly from organisms in the previous generation.

• Over long periods of time, these small differences accumulate to produce MAJOR transformation.

NATURAL SELECTION: the mechanism of evolution*

• 1.) Individual members of a population differ from one another.

• 2.) Some of those differences are due to characteristics that can be passed from parent to offspring.

• 3.) In each generation, some individuals in a population survive and reproduce, but others do not.

• 4.) Whether an individual lives or dies is not by chance/luck. Those who have inherited advantageous traits survive the longest and have the most offspring. This process is called NATURAL SELECTION.

1.) Members differ from one another

• Look around the room….we are all different: height, weight, skin color, eye color, intelligence!

• We now know that this is because of changes in our DNA (what might be called mutations) which produce different phenotypes.

2.) Traits passed on to offspring

• No “proof” of this was available in the early 1800’s (Mendel didn’t come along until late 1800’s)

• But now we know that traits are passed to offspring

3.) Some survive, some don’t

• Darwin knew that, for instance, one pair of elephants could produce 19 million offspring if they lived a full life and reproduced as often as they could….but there aren’t 19million elephants…so some died.

4.) Survival and reproduction are not random….*

• Evidence suggests that survival and reproductive success depends on an individual’s characteristics.

– Large male elephant seals have more offspring, because females are attracted to larger males

– Snapdragon flowers produce more white offspring than yellow ones because pollinators are attracted to the white flowers more

– Antibiotic resistant bacteria grow faster than non-resistant ones

– The “winners” in the competition to survive win because they have specific traits.

– Over time, the population changes as these specific traits are passed on.

Proof of Evolution*

• 1.) Fossils• 2.) Comparative Anatomy

– Homologous Structures– Vestigial Structures

• 3.) Embryologic Similarity: all vertebrate structures look similar to each other early in their development

• 4.) Biochemical proof: DNA

1.) Fossils

• new species evolved from, and replaced, older ones

• Ex: whales evolved from four-legged land dwellers

2.) Comparative Anatomy

• Homologous Structures: body structure is modified by evolution to serve different functions in different species, but all of these organisms have a COMMON ancestor from which they evolved.– Forelimbs of birds/mammals (Fig 14-8) have

all of the same internal anatomy, but look very different (paws, feet, wings, flippers)

Fig. 14-8

Pterodactyl

Bird

Bat

Dolphin

Seal

Dog

Sheep Shrew

humerus

ulna

metacarpalsphalanges

radiuscarpals

Human

GRASPINGRUNNINGSWIMMINGFLYING

Comparative Anatomy

• Vestigial Structures: structures that serve no apparent purpose in a more advanced organism, but was useful in an earlier organism– Appendix: no use in humans, helped in digesting plants

back when humans and their predecessors ate only plants

– Pelvic bones in whales: they don’t need them to swim, but have them

– Other examples: wisdom teeth, arrector pili muscles, coccyx

Vestigial Structures

Fig. 14-9

These vestigial bones are similar in structure to those of the salamander but serve no function; all three animals inherited the bones from a common ancestor

The bones of a salamander’s hindlimbfunction in support and locomotion

(c) Boa constrictor

(b) Baleen whale

(a) Salamander

3.) Embryologic Similarity*

• Ancestral vertebrates possessed genes (HOX genes) that directed the development of gills and tails. All of their descendants still have those genes.

• In fish, those genes are active (protein synthesis) all the way through development and fish are BORN with gills and tails.

• In humans and chickens, these genes are shut off at some point in development, because we are born without gills/tails.

Embryological Stages Reveal Evolutionary Relationships

Fig. 14-11

Proof of natural selection

• The breeding of domestic plants and animals to produce desirable features is something humans have done for thousands of years.

• We have artificially bred dogs to the point that there are breeds of dogs that look COMPLETELY different (Great Dane vs Chihuahua) yet they belong to the same species. This was done by selecting the individuals from each litter that had more of the desirable traits and breeding them (Great Dane: bred the biggest puppies of the litter or Chihuahua: bred the smallest dogs, etc)

It’s still happening

• Roaches in Florida resistant to Combat: developed a mutation that caused them to dislike glucose!

Two final points*

• The variations on which natural selection works are produced by random mutations.

• Natural selection favors organisms that are best adapted to a particular environment at a particular time. (If environment changes, then the traits that organisms need to survive may change too.