Family tree <ul><li>The process of evolution produces a pattern of relationships between species </li></ul><ul><li>As lineages evolve and split and modifications are inherited, their evolutionary paths diverge. This produces a branching pattern of evolutionary relationships. </li></ul>
Studying the inherited species……. <ul><li>characteristics and other historical evidence, we can reconstruct evolutionary relationships and represent them on a “family tree,” called a phylogeny. </li></ul>
Three domains: <ul><li>The family tree is a hypothesis about the realtionships among organisms. </li></ul><ul><li>It illustrates the idea that all of life is related and can be divided into three major clades, </li></ul><ul><li>Three major clades: </li></ul><ul><li>a) Archaea b) Bacteria c) Eukaryota </li></ul>
Understanding Phylogenies <ul><li>The root of the tree represents the ancestral lineage, and the tips of the branches represent the descendents of that ancestor. As you move from the root to the tips, you are moving forward in time. </li></ul>
<ul><li>When a lineage splits (speciation), it is represented as branching on a phylogeny. When a speciation event occurs, a single ancestral lineage gives rise to two or more daughter lineages. </li></ul>
<ul><li>Phylogenies trace patterns of shared ancestry between lineages. Each lineage has a part of its history that is unique to it alone and parts that are shared with other lineages. </li></ul>
<ul><li>Similarly, each lineage has ancestors that are unique to that lineage and ancestors that are shared with other lineages—common ancestors. </li></ul>
<ul><li>A clade is a grouping that includes a common ancestor and all the descendents (living and extinct) of that ancestor. Using a phylogeny, it is easy to tell if a group of lineages forms a clade. Imagine clipping a single branch off the phylogeny—all of the organisms on that pruned branch make up a clade. </li></ul>
<ul><li>Clades are nested within one another—they form a nested hierarchy. A clade may include many thousands of species or just a few. Some examples of clades at different levels are marked on the phylogenies below. Notice how clades are nested within larger clades. </li></ul>
Trees, Not Ladders <ul><li>Similarly, it’s easy to misinterpret phylogenies as implying that some organisms are more “advanced” than others; however, phylogenies don’t imply this at all. </li></ul>
<ul><li>So when reading a phylogeny, it is important to keep three things in mind: </li></ul><ul><li>1.Evolution produces a pattern of relationships A B C D among lineages that is tree-like, not ladder-like. </li></ul>
<ul><li>2. Just because we tend to read phylogenies from left to right, there is no correlation with level of “ advancement.” </li></ul>
<ul><li>3. For any speciation event on a phylogeny, the choice of which lineage goes to the right and which goes to the left is arbitrary. The following phylogenies are equivalent: </li></ul>
Misconceptions about humans <ul><li>It is important to remember that: </li></ul><ul><li>1. Humans did not evolve from chimpanzees. Humans and chimpanzees are evolutionary cousins and share a recent common ancestor that was neither chimpanzee nor human. </li></ul>2. Humans are not “higher” or “more evolved” than other living lineages. Since our lineages split, humans and chimpanzees have each evolved traits unique to their own lineages.
<ul><li>Shared derived characters can be used to group organisms into clades. For example, amphibians, turtles, lizards, snakes, crocodiles, birds and mammals all have, or historically had, four limbs. </li></ul>However, the presence of four limbs is not useful for determining relationships within the clade in green above, since all lineages in the clade have that character. To determine the relationships in that clade, we would need to examine other characters that vary across the lineages in the clade.
<ul><li>We use homologous characters—characters in different organisms that are similar because they were inherited from a common ancestor that also had that character. An example of homologous characters is the four limbs of tetrapods . Birds, bats, mice, and crocodiles all have four limbs. Sharks and bony fish do not. </li></ul><ul><li>The ancestor of tetrapods evolved four limbs, and its descendents have inherited that feature—so the presence of four limbs is a homology. </li></ul>
Not all characters are homologies <ul><li>For example, birds and bats both have wings, while mice and crocodiles do not. Does that mean that birds and bats are more closely related to one another than to mice and crocodiles? No. When we examine bird wings and bat wings closely, we see that there are some major differences. </li></ul>
<ul><li>Bat wings consist of flaps of skin stretched between the bones of the fingers and arm. Bird wings consist of feathers extending all along the arm. These structural dissimilarities suggest that bird wings and bat wings were not inherited from a common ancestor with wings. </li></ul>
<ul><li>Bird and bat wings are analogous—that is, they have separate evolutionary origins, but are superficially similar because they evolved to serve the same function. Analogies are the result of convergent evolution. </li></ul>Interestingly, though bird and bat wings are analogous as wings, as forelimbs they are homologous. Birds and bats did not inherit wings from a common ancestor with wings, but they did inherit forelimbs from a common ancestor with forelimbs.
<ul><li>Biologists use phylogenetic trees for many purposes, including: </li></ul><ul><li>1. Testing hypotheses about evolution </li></ul><ul><li>2. Learning about the characteristics of extinct species and ancestral lineages </li></ul><ul><li>3. Classifying organisms </li></ul>
Types of clades <ul><li>Monophyletic taxon : A group composed of a collection of organisms, including the most recent common ancestor of all those organisms and all the descendants of that most recent common ancestor. </li></ul><ul><li>. </li></ul>Examples : Mammalia, Aves (birds), angiosperms, insects, etc.
A group containing an ancestor and all of its descendants - defined by one or more synapomorphies. Shared Derived Character = Synapomorphy
<ul><li>Paraphyletic taxon : A group composed of a collection of organisms, including the most recent common ancestor of all those organisms. Unlike a monophyletic group, a paraphyletic taxon does not include all the descendants of the most recent common ancestor. </li></ul>Examples : Traditionally defined Dinosauria, fish, gymnosperms, invertebrates, protists, etc.
A group consisting of an ancestor but not all of its descendants. It is defined by what it does not have.
<ul><li>Polyphyletic taxon : A group composed of a collection of organisms in which the most recent common ancestor of all the included organisms is not included, usually because the common ancestor lacks the characteristics of the group. </li></ul>Examples : marine mammals, bipedal mammals, flying vertebrates, trees, algae, etc.
A group that does not include the common ancestor of the group. The common ancestor is placed in another group.
<ul><li>Out Group: A group outside the groups in question which is used to define the polarity of character transformations (primitive to derived). </li></ul><ul><li>Sister Group: A monophyletic group more closely related to the group under examination than any other group. </li></ul>
<ul><li>Copyright 2006 by The University of California Museum of Paleontology, Berkeley, and the Regents of the University of California. All materials appearing on the UCMP Web Servers (WWW.UCMP.BERKELEY.EDU, EVOLUTION.BERKELEY.EDU) </li></ul>