Evolution What is Natural Selection?

Notes: Darwin’s Voyage

Darwin’s Epic Journey Darwin developed a scientific theory of biological evolution that explains how modern organisms evolved over long periods of time through descent from common ancestors Charles Darwin

Darwin’s Epic Journey Darwin was invited to sail on the HMS Beagle’s five-year voyage mapping the coastline of South America. Darwin planned to collect specimens of plants and animals on the voyage. No one knew it, but this would be one of the most important scientific voyages in history.

Pattern’s of Biodiversity Species Vary Globally Example: Darwin found flightless, ground-dwelling birds called rheas living in the grasslands of South America. Rheas look and act a lot like ostriches. Yet rheas live only in South America, and ostriches live only in Africa.

Pattern’s of Biodiversity Species Vary Locally Example: The shape of the tortoises’ shells corresponds to different habitats.

Species Vary Locally Darwin noticed several types of small brown birds on the islands with beaks of different shapes. He didn’t consider these smaller birds to be unusual or important—at first.

Pattern’s of Diversity Species vary over time Darwin noticed that some fossils of extinct animals were similar to living species.

Darwin’s Conclusion The evidence suggested that species are not fixed and that they could change by some natural process. Organism change over time. Evolution occurs by Natural Selection

Evolution What is Natural Selection?

Notes: Evolution By Natural Selection Natural selection occurs in any situation in which more individuals are born than can survive (the struggle for existence), there is natural heritable variation (variation and adaptation), and there is variable fitness among individuals (survival of the fittest).

Natural Selection

Natural Selection Natural selection is the process by which organisms with variations most suited to their local environment survive and leave more offspring. In natural selection, the environment—not a farmer or animal breeder—influences fitness.

Natural Selection- Example This hypothetical population of grasshoppers changes over time as a result of natural selection. Grasshoppers can lay more than 200 eggs at a time, but only a small fraction of these offspring survive to reproduce.

Natural Selection- Example Certain variations, called adaptations, increase an individual’s chances of surviving and reproducing. In this population of grasshoppers, heritable variation includes yellow and green body color. Green color is an adaptation: The green grasshoppers blend into their environment and so are less visible to predators.

Natural Selection- Example Because their color serves as a camouflage adaptation, green grasshoppers have higher fitness and so survive and reproduce more often than yellow grasshoppers do.

Natural Selection- Example Green grasshoppers become more common than yellow grasshoppers in this population over time because more grasshoppers are born than can survive, individuals vary in color and color is a heritable trait, and green grasshoppers have higher fitness in this particular environment

Natural Selection Natural selection does not make organisms “better.” If local environmental conditions change, some traits that were once adaptive may no longer be useful. If environmental conditions change faster than a species can adapt to those changes, the species may become extinct.

Common Descents Darwin proposed that, over many generations, adaptation could cause successful species to evolve into new species. Principle of common descent suggest that, all species—living and extinct— are descended from ancient common ancestors. For evidence of descent with modification over long periods of time, Darwin pointed to the fossil record.

Exit Ticket There are two types of worms. Worms that eat in the day time and worms that eat at night. If most birds eat during the day time, which adaptation has a higher fitness? Explain your reasoning.

Evolution What is Natural Selection?

Notes: Evidence of Evolution Biogeography Age of the Earth Homologous Structures Vestigial Structures Genetic Code

Biogeography Patterns in the distribution of living and fossil species tell us how modern organisms evolved from their ancestors. The first is a pattern in which closely related species differentiate in slightly different climates. The second is a pattern in which very distantly related species develop similarities in similar environments.

Age of Earth and Fossil Fossils form series that trace the evolution of modern species from extinct ancestors. Geologists now use radioactivity to establish the age of certain rocks and fossils. Radioactive dating indicates that Earth is about 4.5 billion years old—plenty of time for evolution by natural selection to take place.

Embryology Same groups of embryonic cells develop in the same order and in similar patterns to produce many homologous tissues and organs in vertebrates.

Homologous Structures Structures that are shared by related species and that have been inherited from a common ancestor are called homologous structures.

Analogous Structures Body parts that share a common function, but not structure, are called analogous structures.

Vestigial Structures Vestigial structures are inherited from ancestors, but have lost much or all of their original function due to different selection pressures acting on the descendant.

Genetic Code This genetic code is nearly identical in almost all organisms, including bacteria, yeasts, plants, fungi, and animals. This similarity in genetic code is powerful evidence that all organisms evolved from common ancestors.

Evolution What is Natural Selection?

Notes: Primate Evolution =BpnlS_ach- 0&list=PLSyev41swmDJj9yMmAH- fhoIshPGMRgg8&index=6 =BpnlS_ach- 0&list=PLSyev41swmDJj9yMmAH- fhoIshPGMRgg8&index=6 Humans appeared late in Earth’s history.

Primates Characteristics Humans share a common ancestor with other primates. Primates are mammals with flexible hands and feet, forward-looking eyes and enlarged brains.

Primate Characteristic Primates evolved into prosimians and anthropoids. Prosimians are the oldest living primates. They are mostly small and nocturnal.

Primate Characteristic Anthropoids are humanlike primates. They are subdivided into the New World monkeys, Old World monkeys, and hominoids. Homonoids are divided into hominids, great apes, and lesser apes. Hominids include living and extinct humans.

Human Characteristics –Bipedal motion (walking on two legs) –foraging –carrying infants and food –using tools Walking upright has important adaptive advantages.

Most hominids are either the genus Australopithecus or Homo. Australopithecines were a successful genus. The Homo genus first evolved 2.4 million years ago. Oldest Ancestor- “Lucy”

Modern Human Homo sapiens fossils date to 200,000 years ago. Human evolution is influenced by a tool-based culture. There is a trend toward increased brain size in hominids. Australopithecus afarensis Homo habilisHomo neanderthalensis Homo sapiens

Lice and Human Evolution

Evolution What is Natural Selection?

Notes: Evolution of a Population

THINK ABOUT IT Insect populations often contain a few individuals that are resistant to a particular pesticide. Those insects pass on their resistance to their offspring and soon the pesticide-resistant offspring dominate the population. The relationship between natural selection and genetics explains how pesticide resistance develops

Natural Selection on Single-Gene Traits Natural selection for a single-gene trait can lead to changes in the amount of genes in a population and then to evolution. For example, a mutation in one gene that determines body color in lizards can affect their lifespan. So if the normal color for lizards is brown, a mutation may produce red and black forms.

Natural Selection on Single-Gene Traits: The example of Lizard Color If red lizards are more visible to predators, they might be less likely to survive and reproduce. Therefore the allele for red coloring might not become common. Black lizards might be able to absorb sunlight. Higher body temperatures may allow the lizards to move faster, escape predators, and reproduce.

Natural Selection on Polygenic Traits Polygenic traits have a range of phenotypes that often form a bell curve. The fitness of individuals may vary from one end of the curve to the other. Natural selection can affect the range of phenotypes creating the shape of the bell curve.

Directional Selection For example, if only large seeds were available, birds with larger beaks would have an easier time feeding and would be more successful in surviving and passing on genes.

Stabilizing Selection For example, very small and very large babies are less likely to survive than average-sized individuals. The fitness of these smaller or larger babies is therefore lower than that of more average- sized individuals.

Disruptive Selection For example, in an area where medium-sized seeds are less common, birds with unusually small or large beaks would have higher fitness. Therefore, the population might split into two groups—one with smaller beaks and one with larger beaks

Genetic Drift Over time, a series of chance occurrences can cause an allele to become more or less common in a population.

Bottleneck Effect The bottleneck effect is a change in gene frequency following a dramatic reduction in the size of a population. For example, a disaster may kill many individuals in a population, and the surviving population’s gene pool may contain different gene frequencies from the original gene pool.

Evolution What is Natural Selection?