Patterns Of Evolution. 17.4 Notes. Patterns of Evolution. Large scale evolutionary patterns that occur over long periods of time are called macroevolution. Macro = large Evolution = Change over time There are six important topics we will talk about today…. Patterns Of Evolution.
Patterns Of Evolution 17.4 Notes
Patterns of Evolution Large scale evolutionary patterns that occur over long periods of time are called macroevolution. Macro= large Evolution= Change over time There are six important topics we will talk about today…
Patterns Of Evolution • Extinction • Adaptive Radiation • Convergent Evolution • Coevolution • Punctuated Equilibrium/Gradualism • Developmental Genes and Body Plans
1. Extinction More than 99% of all species that have ever lived are now extinct! Two reasons for extinctions are • Competition for resources (food, water, shelter) • Environmental changes Some species adapt and survive while others gradually became extinct in ways that are often caused by natural selection.
a. Mass Extinctions Mass extinctions have occurred several times in Earth’s history. These are probably caused by many factors but researchers have not yet determined the precise cause. ???
Effects of Mass Extinction The disappearance of so many species left habitats open and provided ecological support for those organisms that survived. The result was often a burst of evolution that produced many new species. Example: the extinction of dinosaurs cleared the way for the evolution of modern mammals and birds.
Adaptive Radiation A single species or a small group of species has evolved through natural selection and other processes into diverse forms that live in different ways. Example: Darwin’s finches! There are more than a dozen species found on islands that evolved from a single species from South America.
Convergent Evolution Adaptive radiations can have an interesting evolutionary side effect. They can produce unrelated organisms that looks remarkably similar to one another. This is called convergent evolution and it has occurred in plants and animals.
Convergent Evolution Example: Swimming animals involving fish, mammals (dolphins) and birds (penguins) have similar structures that look and function similar but do not share a common evolutionary history. These structures are called analagous. Ex. Dolphin’s fluke and a fish tail
Coevolution Sometimes organisms that are closely connected to one another by ecological interaction evolve together. Example: Flowering plants and a specific pollinator Two species evolve in response to changes in each other.
Coevolution Orchid from Madagascar has a supply of nectar within its tip that is 40 cm long. The hawk moth of Madagascar has an equally long feeding tube.
5. Punctuated Equilibrium A population of organisms can change gradually or rapidly over time. Some biologists suggest that most new species are produced by periods of rapid change. This rapid evolution after long periods of equilibrium can occur for several reasons…
Punctuated Equilibrium • A small population becomes isolated from the main part of the population. Genetic changes can spread more quickly among fewer individuals. • A small group of organisms migrates to a new environment. Example: Galapago’s finches. * Organisms evolve rapidly to fill available niches.
Scientists term punctuated equilibrium to describe this pattern of long, stable periods interrupted by brief periods of more rapid change.
The theory of Gradualism involves a slow, steady change in a particular line of descent. The fossil record confirms that populations of organisms did change gradually over time. The concepts of punctuated equilibrium and gradualism are still controversial among biologists today.
6. Developmental Genes and Body Plans Changes in the expression of developmental genes may explain differences in ancient and modern body plans. Small changes in the activity of control genes can affect many other genes to produce large changes in adult animals.
Example Some ancient insects had wing-like structures on all body segments while modern insects have wings only on one or two segments. Changes in the activation of this gene could have enabled many winged ancestors of modern insects to evolve into 4 winged and 2 winged forms.