Chapter 10 Evolution and Natural Selection

How could evolution lead to this?

Charles Darwin ( ) Collected plant & animal specimens during his 5-year voyage on the HMS Beagle Published his famous book, 30 years later in 1859, “The Origin of Species by means of Natural Selection.”

While on the HMS Beagle Darwin’s journey allowed him to appreciate the diversity of life It is estimated that today we have between 3 & 20 million different species Through very careful observations, Darwin began to question what he saw

Voyage of the HMS Beagle Stopped in Galapagos Islands –500 miles off coast of Ecuador

Galapagos Recently formed volcanic islands. Most of animals on the Galápagos live nowhere else in world, but they look like species living on South American mainland. 800 km west of Ecuador

Many of Darwin’s observations made him wonder… Why? Darwin asked: Why were these creatures found only on the Galapagos Islands? Darwin found…many unique species

Darwin observed differences among island species. Variation is a difference in a physical trait. –Galápagos tortoises that live in areas with tall plants have long necks and legs. –Galápagos finches that live in areas with hard- shelled nuts have strong beaks.

Darwin found: Different shells on tortoises on different islands Darwin asked: Is there a relationship between the environment & what an animal looks like?

Darwin was amazed to find out: All 14 species of birds were finches… Finch?Sparrow? Woodpecker? Warbler? Finch?Sparrow? Woodpecker? Warbler? But Darwin found… a lot of finches Large ground finch Small ground finch Warbler finchTree finch But there is only one species of finch on the mainland! Darwin asked: If the Galapagos finches came from the mainland, why are they so different now?

Finch?Sparrow? Woodpecker? Warbler? The finches cinched it! Large ground finch Small ground finch Warbler finchTree finch Big seed eaterSmall seed eater Insect eaterLeaf & bud eater Darwin said: Ahaaaa! A flock of South American finches were stranded on the Galapagos… Darwin found: The differences between species of finches were associated with the different food they ate. different beaks are inherited variations serve as adaptations that help birds compete for food these birds survive & reproduce pass on the genes for those more fit beaks over time nature selected for different species with different beaks

Relationship between species (beaks) & food

An adaptations is a feature that allow an organism to better survive in its environment. –Species are able to adapt to their environment. –Adaptations can lead to changes in the frequencies of alleles in the population.

Darwin found fossils of extinct animals that resemble modern animals. Darwin found fossil shells high up in the Andes mountains. Darwin observed fossil and geologic evidence supporting an ancient Earth.

He saw land move from underwater to above sea level due to an earthquake. Darwin extended his observations to the evolution of organisms. Geological Evidence

1. LaMarck –evolution by acquired traits creatures developed traits during their lifetime give those traits to their offspring –example in reaching higher leaves giraffes stretch their necks & give the acquired longer neck to offspring –not accepted as valid Earlier ideas on Evolution Ideas that shaped Darwins Theory

Ancient, Changing Earth 2. Charles Lyell ( ) Close, influential friend of Darwin. Observations explain that past events shaped the earth by slow-moving forces still in operation today, acting over a very long period of time Darwin asked: If earth could change over time, then couldn’t life change as well?

3. Thomas Malthus Human population is kept in check by famine, disease, and competition for resources Darwin thought that plants and animals compete for resources as well. Only the ‘fittest” win the competition.

20 years after the voyage on the Beagle … 4. Alfred Russel Wallace sent Darwin a short essay that summarized conclusions like Darwin’s thoughts about evolution. Prompted Darwin to publish his own book - On the Origin of Species by Means of Natural Selection.

Several key insights led to Darwin’s idea for natural selection. Artificial selection is the process by which humans select traits through breeding. neck feathers crop tail feathers

Darwin’s Hypothesis: Natural selection is a mechanism by which individuals that have inherited beneficial adaptations produce more offspring on average than do other individuals. Heritability is the ability of a trait to be passed down. There is a struggle for survival due to overpopulation and limited resources.

There are four main principles to the theory of natural selection. Variation –slight differences in traits in a population Natural selection explains how evolution can occur. overproduction – more offspring produced than needed to replace yourself Adaptation – variation that allows better chance for survival descent with modification – over time population increases fitness for survival VARIATION OVERPRODUCTION ADAPTATION Fitness is the measure of survival ability and ability to produce more offspring. DESCENT with MODIFICATION

Natural selection can act only on traits that already exist. Structures take on new functions in addition to their original function. Natural selection acts on existing variation. wrist bone five digits

Evidence for evolution in Darwin’s time came from several sources. Fossils provide evidence of evolution. Relative Dating: Fossils in older layers are more primitive than those in the upper layers.

Fossils provide a record of evolution. Paleontology is the study of fossils or extinct organisms.

The study of geography provides evidence of evolution. –island species most closely resemble nearest mainland species –populations can show variation from one island to another

Embryology provides evidence of evolution. Larva Adult barnacle Adult crab –identical larvae, different adult body forms –similar embryos, diverse organisms

The study of anatomy provides evidence of evolution. Human hand Bat wingMole foot –Homologous structures are similar in structure but different in function. –Homologous structures are evidence of a common ancestor.

Human hand Bat wing Mole foot Fly wing –NOT evidence of a common ancestor. The study of anatomy provides evidence of evolution. –Analogous structures have a similar function, different structure.

Vestigial structures are remnants of organs or structures that had a function in an early ancestor. Ostrich wings are examples of vestigial structures. Structural patterns are clues to the history of a species.

Paleontology provides evidence to support evolution. Ex: Transitional Fossils

Biochemical evidence support fossil and anatomical evidence. Two closely-related organisms will have similar DNA sequences. Ex: DNA Sequence Analysis More DNA differences = more time for Mutations to occur = more distantly Related species

Pseudogenes are sequences providing evidence of evolution. –no longer function –carried along with functional DNA –can be clues to a common ancestor: Functioning genes may be similar in organisms with similar lifestyles, but similarities between pseudogenes must reflect a common ancestor

Hox genes – type of homeobox genes found in all vertebrates Homeobox genes – play important roles in the developmental processes of many multicellular organisms. Found in all animal phyla examined so far.

Protein Comparisons. Reveals similarities among cell types of different organisms by comparing their proteins. Cells from different species that have the same proteins most likely come from a common ancestor.

Scientist from any fields contribute to the understanding of evolution. The basic principles of evolution are used in many scientific fields. Evolution unites all fields of biology.