EvolutionEvolution

Change over time (LOTS of TIME!)Change over time (LOTS of TIME!)

http://evolution.berkeley.edu/evolibrary/article/0_0_0/evo_02

The definitionBiological evolution, simply put, is

descent with modification

ModificationModification The central idea of biological evolution is that all life on The central idea of biological evolution is that all life on

Earth shares a common Earth shares a common ancestorancestor, just as you and your , just as you and your cousins share a common grandmother.cousins share a common grandmother.

Through the process of descent with modification, the Through the process of descent with modification, the common ancestor of life on Earth gave rise to the fantastic common ancestor of life on Earth gave rise to the fantastic diversity that we see documented in the fossil record and diversity that we see documented in the fossil record and around us today. Evolution means that we're all distant around us today. Evolution means that we're all distant cousins: humans and oak trees, hummingbirds and whales.cousins: humans and oak trees, hummingbirds and whales.

Modifications Modifications diversity to fit an available niche (lifestyle)

The history of life: The history of life: looking at the patternslooking at the patterns

The central ideas of The central ideas of evolution are that life evolution are that life has a historyhas a history

Life has changed over Life has changed over time time

Different species Different species share common share common ancestors.ancestors.

The family treeThe family tree

The process of The process of evolution produces a evolution produces a pattern of relationships pattern of relationships between species. between species.

This produces a This produces a branching pattern of branching pattern of evolutionary evolutionary relationships.relationships.

Phylogeny constructs Phylogeny constructs these treesthese trees

Understanding a phylogeny is a lot like reading a family tree. Understanding a phylogeny is a lot like reading a family tree. The root of the tree represents the ancestral lineage, and the The root of the tree represents the ancestral lineage, and the tips of the branches represent the descendents of that tips of the branches represent the descendents of that ancestor. ancestor.

a) As you move from the root to the tips, you are moving forward in time.

b) When a lineage splits (speciation), it is represented as branching.

c) Phylogenies trace patterns of shared ancestry between lineages.

Each lineage has a part of its history Each lineage has a part of its history that is unique to it alone and parts that is unique to it alone and parts that are shared with other lineages.that are shared with other lineages.

Similarly, each lineage has ancestors Similarly, each lineage has ancestors that are unique to that lineage and that are unique to that lineage and ancestors that are shared with other ancestors that are shared with other lineages — lineages — common ancestorscommon ancestors..

Trees, not ladders

Aristotle's vision of a Great Chain of Being, Aristotle's vision of a Great Chain of Being, above. We now know that this idea is incorrect.above. We now know that this idea is incorrect.

Similarly, it's easy to misinterpret phylogenies Similarly, it's easy to misinterpret phylogenies as implying that some organisms are more as implying that some organisms are more "advanced" than others; however, phylogenies "advanced" than others; however, phylogenies don't imply this at all.don't imply this at all.

In the phylogeny above it is equally valid to list In the phylogeny above it is equally valid to list events from right to left or left to right. events from right to left or left to right.

Ferns are no more “advanced” than mossFerns are no more “advanced” than moss

Misconceptions about humansMisconceptions about humans

Humans did not evolve from chimpanzees.

Humans and chimpanzees are Humans and chimpanzees are evolutionary cousins and share evolutionary cousins and share a recent common ancestor that a recent common ancestor that was neither chimpanzee nor was neither chimpanzee nor human.human.

Humans are not "higher" or Humans are not "higher" or "more evolved" than other "more evolved" than other living lineages. living lineages.

Since our lineages split, Since our lineages split, humans and chimpanzees humans and chimpanzees have each evolved traits have each evolved traits unique to our own lineages.unique to our own lineages.

Using shared derived charactersUsing shared derived characters

Our goal is to find Our goal is to find evidence that will help evidence that will help us group organisms us group organisms into less and less into less and less inclusive groups.inclusive groups.

Phylogenetic TreePhylogenetic Tree

HomologiesHomologies

Homologies and analogiesHomologies and analogies Since a phylogenetic tree is a hypothesis about Since a phylogenetic tree is a hypothesis about

evolutionary relationships, we want to use characters evolutionary relationships, we want to use characters that are reliable indicators of common ancestry to that are reliable indicators of common ancestry to build that tree. build that tree.

Homologous (common inheritance) a) Homology = An example is the presence of four limbs.

AnalogiesAnalogiesb) Analogy –same function,

different evolution Bat and bird wings are examples of analogies

Not all characters are Not all characters are homologies. For example, homologies. For example, birds and bats both have birds and bats both have wings, while mice and wings, while mice and crocodiles do not. crocodiles do not.

Does that mean that birds and Does that mean that birds and bats are more closely related bats are more closely related to one another than to mice to one another than to mice and crocodiles? and crocodiles?

No. When we examine bird No. When we examine bird wings and bat wings closely, wings and bat wings closely, we see that there are some we see that there are some major differences.major differences.

Analogies…Analogies… hint at hint at differentdifferent ancestors ancestors

Bat wings consist of flaps of Bat wings consist of flaps of skin stretched between the skin stretched between the bones of the fingers and arm. bones of the fingers and arm.

Bird wings consist of feathers Bird wings consist of feathers extending all along the arm. extending all along the arm.

These structural dissimilarities These structural dissimilarities suggest that bird wings and suggest that bird wings and bat wings were not inherited bat wings were not inherited from a common ancestor with from a common ancestor with wings. wings.

This idea is illustrated by the This idea is illustrated by the phylogeny, which is based on phylogeny, which is based on a large number of other a large number of other characters. characters.

TIME ( Millions of Years)TIME ( Millions of Years) Adding time to the treeAdding time to the tree If you wanted to squeeze the 3.8 If you wanted to squeeze the 3.8

billion years of the history of life on billion years of the history of life on Earth into a single minute, you Earth into a single minute, you would have to wait about 50 would have to wait about 50 seconds for multicellular life to seconds for multicellular life to evolve, another four seconds for evolve, another four seconds for vertebrates to invade the land, and vertebrates to invade the land, and another four seconds for flowers to another four seconds for flowers to evolve — and only in the last 0.002 evolve — and only in the last 0.002 seconds would "modern" humans seconds would "modern" humans arise.arise.

The following phylogeny The following phylogeny represents vertebrate evolution — represents vertebrate evolution — just a small blade on the tree of life. just a small blade on the tree of life. The lengths of the branches have The lengths of the branches have been adjusted to show when been adjusted to show when lineages split and went extinct.lineages split and went extinct.

How we know what happened when?How we know what happened when?

Life began 3.8 billion years ago, and insects Life began 3.8 billion years ago, and insects diversified 290 million years ago, but the diversified 290 million years ago, but the human and chimpanzee lineages diverged human and chimpanzee lineages diverged only five million years ago.only five million years ago.

a) This long span of time allows for the slow changes of evolution to accumulate.

i. Radiometric i. Radiometric datingdating relies on half-life decay of radioactive elements to allow scientists to date rocks and materials directly.

ii. Stratigraphyii. Stratigraphy provides a sequence of events from which relative dates can be extrapolated.

iii Molecular clocksiii Molecular clocks Mutation rates can give us the years since two species separated..

How?How?

Descent with modificationDescent with modification

We've defined evolution as descent with We've defined evolution as descent with modification from a common ancestor, but modification from a common ancestor, but exactly what has been modified? Evolution exactly what has been modified? Evolution only occurs when there is a change in only occurs when there is a change in gene frequencygene frequency within a within a populationpopulation over over time. time.

These genetic differences are heritable and can be passed on to the next generation — which is what really matters in evolution: long term change.

Natural SelectionNatural Selection Increasing the amount of a certain gene (trait) over

time due to an advantage gained from that trait. Imagine that green beetles are easier for birds to spot (and Imagine that green beetles are easier for birds to spot (and

hence, eat). Brown beetles are a little more likely to survive hence, eat). Brown beetles are a little more likely to survive to produce offspring. They pass their genes for brown to produce offspring. They pass their genes for brown coloration on to their offspring. So in the next generation, coloration on to their offspring. So in the next generation, brown beetles are more common than in the previous brown beetles are more common than in the previous generation. generation.

Genetic driftGenetic drift

Genetic driftGenetic driftMore brown genes are present, just by chance!

MigrationMigration Individuals moving introduce a different gene

into a population Some individuals from a population of brown Some individuals from a population of brown

beetles might have joined a population of green beetles might have joined a population of green beetles. That would make the genes for brown beetles. That would make the genes for brown beetles more frequent in the green beetle beetles more frequent in the green beetle population. population.

MutationMutation A DNA mistake introduces a new allele of a gene

into a population A mutation could cause parents with genes for A mutation could cause parents with genes for

bright green coloration to have offspring with a bright green coloration to have offspring with a gene for brown coloration. That would make the gene for brown coloration. That would make the genes for brown beetles more frequent in the genes for brown beetles more frequent in the population. population.

Mutation story…Mutation story…

Developmental changesDevelopmental changes Changes in how an organism grows introduce a

trait giving some advantage. Developmental changes may help explain, for Developmental changes may help explain, for

example, how some hoofed mammals evolved into example, how some hoofed mammals evolved into ocean-dwellers, how water plants invaded the land, ocean-dwellers, how water plants invaded the land, and how small, armored invertebrates evolved wings.and how small, armored invertebrates evolved wings.

Learning about Learning about evolutionary historyevolutionary history

An organism's An organism's development may development may contain clues about contain clues about its history that its history that biologists can use to biologists can use to build evolutionary build evolutionary trees. trees.

Embryology videoEmbryology video

Human activityHuman activity Human selections can

modify a population of organisms.

A striking example is A striking example is that of the population that of the population of dark moths in the of dark moths in the 19th century in 19th century in England, which rose England, which rose and fell in parallel to and fell in parallel to industrial pollution. industrial pollution. These changes can These changes can often be observed and often be observed and documented. documented.

Choice of MateChoice of Mate

Sexual selection Sexual selection Individuals must be chosen to mate for genes to be passed on.

No kids, no No kids, no evolutionary evolutionary “success”.“success”.

Artificial selectionArtificial selection One of my favorite portions of Charles Darwin’s One of my favorite portions of Charles Darwin’s

Origin of SpeciesOrigin of Species are his opening chapters detailing are his opening chapters detailing the very successful the very successful human efforts at selection..

AdaptationsAdaptations

Mimicry of leaves by by insects is an insects is an adaptation for adaptation for evading predators. evading predators.

This example is a This example is a katydid from Costa katydid from Costa Rica. Rica.

Mimicry VideoMimicry Video

AdaptationsAdaptations

Tobacco produces nicotine, a potent poison, to kill insect and animal pests.

This reduces This reduces competition for competition for nutrients and water. nutrients and water.

Echolocation in bats is an adaptation for is an adaptation for catching insects. catching insects.

Is evolution progressive?Is evolution progressive?This is not an easy question to answer. This is not an easy question to answer.

From a plant's perspective, the best measure of From a plant's perspective, the best measure of progress might be photosynthetic ability; progress might be photosynthetic ability;

From a spider's it might be the efficiency of a From a spider's it might be the efficiency of a venom delivery system. venom delivery system.

SummarySummary

Evolution = ?Evolution = ? Descent with modification

Mechanisms of evolutionMechanisms of evolutioni. Genetic Driftii. Natural Selectioniii. Mutationiv. Migrationv. Developmental Changes

Why does evolution matter?