Descent With Modification A Darwinian View of Life
The Theory of Evolution by Natural Selection • Charles Darwin, reluctant revolutionary, profoundly altered our view of the natural world and our place in it. • Simple yet at times controversial, misunderstood and misused for social goals, the theory remains unchallenged as the central concept of biology.
What is Evolution? Biological evolution is not simply a matter of change over time. Lots of things change over time: trees lose their leaves, mountain ranges rise and erode, but they aren't examples of biological evolution because they don't involve descent through genetic inheritance.
What is Evolution? • The change in gene frequencies in a population over time
What is evolution? • Organism evolution means changes in populations, species, or groups of species. It occurs because: • Heritable traits vary in a population. • These traits are represented by alleles for genes that modify morphology (form/structure), physiology, or behavior. • There is a struggle for survival and most organisms perish. Only those that survive pass their genes on.
Can individuals Evolve? • NO! • Individuals survive and pass genes on or do not survive to breed. • For an organism to change itself to suit its environment it would need to change the DNA in their gametes- so the “change” could be passed on to the next generation. • Some individuals are better suited for their environment. They leave more offspring. Over generations, the genetic composition of a population reflects more of their “beneficial” genes.
Fitness • It’s not about being the strongest or the biggest or the fastest • It is the combination of physical traits and behavior is what helps organisms survive and reproduce in their environment.
Adaptation • Successful modification or change enables organisms to become better suited to their environment. • It doesn’t happen in a single generation. • Slight differences give advantage • Advantage means survival • Survival means genes are passed on
Some animals are camouflaged to blend in with their surroundings. This keeps them safe as it is more difficult for other animals to see them or catch them for food. This lizards skin is so similar to the rock colour. These zebra could easily be mistaken for bushes from a distance.
Aquatic creatures have streamlined bodies to move more easily in the water. These wings act as flippers
These organisms have adapted to live in the hot climate of the desert. Camels store water in their humps. The cactus has fleshy stems that store water. Ostriches have long eyelashes to keep out the sand.
These animals have adapted to be more suited to cold temperatures. Layers of fat keep the seals body warm, and small ears stop heat loss. Deer have a warm layer of fur. polar bears have black skin to better absorb the sun’s heat
The water provides support for this lily as it has less developed roots to hold it in place. Dandelions seeds are easily dispersed. Cactus have developed spines to protect them from predators
Common descent- if you look back far enough in time all species have shared or have common ancestors.
Natural selection is differential success in reproductionthat results from the interaction between individuals that vary in heritable traits and their environment
Summary • Definition- Evolution is the change in the overall genetic makeup of a population over time • Three Basic Components • Individuals cannot evolve. Populations evolve. • Natural selection is the mechanism of evolution. • Evolution occurs situationally (NOT GOAL ORIENTED).
Natural Selectionin Action • Camouflage
(a) A flower mantidin Malaysia (b) A stick mantidin Africa Figure 22.11 Natural Selection in Action Environmental changes over time
Natural Selection in Action • Eye spots
Natural Selection in Action • Counter Shading
Natural Selection in Action • Disruptive Coloration
Natural Selection in Action • Mimicry • Monarch or Viceroy Butterfly