Transcript Natural selection

VIZUALIZING EARTH HISTORY
By Loren E. Babcock
Chapter 5
Biological Evolution
Evidence of Biological Evolution and Natural Selection
Explain the meaning of biological evolution.
Evolution - Change through time (usually applied to
biological organisms).
Changes that occur within a species or population
from one generation to the next, as parents pass
their morphologic, behavioral, and other traits
on to their offspring, represent microevolution.
Evidence of Biological Evolution and Natural Selection
Darwinian synthesis
By the mid 1800s, biological evolution had become
widely accepted as a scientific theory. Although it
was (and still is) accepted by practicing scientists
with the highest degree of certainty, opinion
differed on its driving force.
The mechanism that drives biological evolution
—natural selection—
was first put forward in separate
publications by Charles Darwin and
Alfred Russell Wallace (1859).
Evidence of Biological Evolution and Natural Selection
Explain natural selection and how it operates.
Natural selection - The process by which individuals
best suited to their environment survive and
reproduce, and less well suited individuals are
eliminated from the population.
To provide supporting evidence for the concept
of natural selection, Darwin addressed embryology,
homologous structures, vestigial structures, breeding
experiments, the fossil record, and adaptation.
Evidence of Biological Evolution and Natural Selection
Explain natural selection and how it operates.
Homologous structures - Morphological features
in biological organisms that have a similar
position and evolutionary origin, but not
necessarily identical structure or the
same function.
Analogous structures - in organisms have essentially the
same function, but different evolutionary origins. Birds,
bats, and insects have all evolved wings for flight, but
they have done so by different evolutionary means.
Evidence of Biological Evolution and Natural Selection
Explain natural selection and how it operates.
Evidence of Biological Evolution and Natural Selection
Explain natural selection and how it operates.
Vestigial structure - Structure in an organism, usually
reduced in size or function compared to the homologue
in earlier species of the evolutionary lineage; it is
in the process of disappearing.
Selective breeding – is a process in which humans
decide which desirable traits should be concentrated
in breeding, is exemplified in the many breeds of
dogs, all of which have a single ancestor, the gray wolf.
Evidence of Biological Evolution and Natural Selection
Explain natural selection and how it operates.
Adaptation - The process of modification of an
organism or its parts making it more fit for survival in
an ecological niche. The word can also refer to a trait
that helps an organism survive in its ecological niche.
Darwin and Wallace separately proposed natural
selection as the mechanism to explain how descent
with modification (or evolution) happened.
Natural selection is based on the observation that
populations (or species) are usually composed
of more individuals than the environment can support.
Variation and Inheritance of Traits
Explain the origin of variation in populations and explain
how changes can be inherited.
Gregor Johann Mendel carried out experiments
on garden peas in the 1850s and 1860s,
demonstrated distinct, replicable patterns underlying
inheritance, and developed a conceptual model for
heritability that explained the patterns.
The work laid the foundation for modern genetics,
which is the branch of biology concerned with
heredity and variation.
Punnett Square
Variation and Inheritance of Traits
Understand the structure of genetic material.
Genetics The branch of biology concerned with heredity and variation.
Genetic changes underlie the morphological changes
recorded in the fossil record. Genetic variation and inheritance
of adaptive traits make natural selection possible.
Genetic changes in modern organisms can be used to track
evolutionary history, and even to provide some sense of the
timing of evolutionary events.
Variation and Inheritance of Traits
Understand the structure of genetic material.
Variation and Inheritance of Traits
Modern genetics: genes, chromosomes, DNA
Gene - Unit of chromosomal information about a
heritable trait that is passed on from parents
to offspring.
Chromosome - Genetic structure by which hereditary
information is physically transmitted from one
generation to the next.
The DNA molecule usually consists of two spiral strands, known
as a double helix. It contains genes, which are the hereditary
units that Mendel thought of as unit factors.
Variation and Inheritance of Traits
Modern genetics: genes, chromosomes, DNA
Cells store genetic information in DNA
(deoxyribonucleic acid) molecules.
In eukaryotes, the DNA resides in the
cell nucleus, but prokaryotes lack a
nucleus to contain the DNA.
Variation and Inheritance of Traits
Modern genetics: genes, chromosomes, DNA
Meiosis - Division of chromosomes to
produce two haploid cells as gametes
necessary for sexual reproduction
are produced.
Mitosis - Division of cell nuclei in which
the parental chromosomal number is
maintained; it is the basis for bodily
growth and asexual reproduction.
Variation and Inheritance of Traits
Mutations, adaptations, and random factors
Mutation - Heritable change in DNA or chromosomal
structure that results in new versions of genes,
and ultimately, of life’s diversity.
Molecular clock - The concept that genetic mutations
occur at a known rate, and if the rate is known, the
number of genetic differences between separate
species can be used to measure the amount of
time that has elapsed since the species diverged.
Variation and Inheritance of Traits
Mutations, adaptations, and random factors
Speciation processes
Speciation - The evolution of a new species from an ancestral species.
Speciation, or the rise of a new species from an ancestral species,
in sexually reproducing organisms, can occur according to one of
three general models.
Allopatric Speciation
Sympatric Speciation
Parapatric Speciation
Speciation: Processes and Rates
Allopatric speciation, emphasizes disruption of gene
flow between populations, usually by some sort of
physical barrier.
Sympatric speciation, involves the rise of a daughter
species from a group of individuals within the geographic
range of an ancestral species.
Parapatric speciation, a daughter species might arise
through hybridization of two populations.
Speciation: Processes and Rates
SpePECIATION PROCESSES
The fossil record shows two different speciation patterns,
cladogenesis and anagenesis.
Cladogenesis is a branching speciation pattern, and it applies
to populations that become reproductively isolated and then
diverge genetically from each other.
Anagenesis refers to changes in allele frequencies that occur
along a single evolutionary pathway. The parent species
and daughter species are connected by intermediates.
Speciation: Processes and Rates
SPECIATION RATES
Charles Darwin’s claimed that evolution occurred
slowly, the result of a gradual accumulation of
changes from one generation to the next and
through phylogeny, or an evolutionary series.
Phylogeny - The line or lines of descent in an evolutionary series.
Phyletic gradualism - Speciation rate characterized by
a slow, gradual pace.
Speciation: Processes and Rates
SPECIATION RATES
Niles Eldredge and Stephen Jay Gould proposed
punctuated equilibrium as a theory of evolutionary biology.
Punctuated equilibrium - sexually reproducing populations
experience little change for most of their geological history,
and that when phenotypic evolution does occur, it is localized
in rare, rapid events of branching speciation (called cladogenesis).
Phyletic gradualism – Contrasts with punctuated equilibrium,
because it states that evolution generally occurs uniformly
and by the steady and gradual transformation of whole
lineages (anagenesis).
Speciation: Processes and Rates
SPECIATION RATES
Phylogenetics: Reconstructing Evolutionary History
Understand how an evolutionary hypothesis is
represented on a cladogram.
A group of species that includes the ancestor and all of its
descendants is called a clade (monophyletic group or natural
group). The classification of species will follow along the lines
of clades, but in practice this is not always the case. Instead,
so-called artificial taxa are used in many circumstances. There
are two basic types of artificial taxa:
1, paraphyletic groups, in which one or more groups descended
from the common ancestor are excluded from the group; and
2, polyphyletic groups, in which members of the group
have separate ancestors.
Evolutionary Patterns and Trends
Study of evolutionary history shows that certain patterns or
trends have occurred in group after group over a period
of millions of years.
IRREVERSIBILITY OF EVOLUTION
Early in the 20th century, the Belgian paleontologist
Louis Dollo observed that evolution cannot produce
exactly the same species more than once. This
concept of the irreversibility of evolution
has come to be known as Dollo’s Law.
Evolutionary Patterns and Trends
CONVERGENT EVOLUTION
Convergent evolution is the evolution of similar body forms in
two or more biological groups. Similar body forms apparently
evolved in different taxa that used similar ecological
strategies, or as a response to similar
ecological pressures.
Adaptive radiation - Rapid evolution of organisms to fill
new ecological niches. Adaptive radiation occurs when
life forms rapidly diverge to fill a variety of niche spaces
that have become open to them.
Speciation: Processes and Rates
SPECIATION RATES
Speciation: Processes and Rates
SPECIATION RATES
Charles Darwin’s claimed that evolution occurred
slowly, the result of a gradual accumulation of
changes from one generation to the next and
through phylogeny, or an evolutionary series.
Phylogeny - The line or lines of descent in an evolutionary series.
Phyletic gradualism - Speciation rate characterized by
a slow, gradual pace.
Evolutionary Patterns and Trends
Adaptive radiations – Increase in body size
In the late 1800s, the American paleontologist
Edward Drinker Cope observed a common tendency
for animals to increase in body size through an evolutionary
lineage. This trend is often called Cope’s Rule.
Horses, for example, were represented in the Eocene by a small
animal known as Hyracotherium. Subsequent horses tended
toward larger size. The living species, Equus caballus, is about
four times the size of Hyracotherium.
Evolutionary Patterns and Trends
Adaptive radiations - Heterochrony
Heterochrony involves evolutionary changes in a lineage
that result from changes in developmental timing.
There are two forms of heterochrony:
Paedomorphosis, adults of the descendant species
look much like juveniles of the ancestor.
Peramorphosis, the onset of sexual maturity in the descendant
is delayed in comparison to the ancestor. The descendant
continues to show development of characters that the
ancestor did not show.
Evolutionary Patterns and Trends
Adaptive radiations - Asymmetry
Natural selection has had a long history of reinforcing
right-left behavioral differences in species.
Ambidextry, or equal capability of the right and
left sides, has tended to be selected against.
It seems more adaptive for individuals to
have a preferred lead side if they are to
perform well in most functions, especially
running or swimming from predators.
Extinction
Extinction is the annihilation of all individuals of a species.
Every species that evolves eventually becomes extinct,
so extinction can be view as a natural part of the
evolutionary process. A certain percentage of the
world’s species can be expected to become extinct
during any interval of geologic time, and the normal
flux of extinction can be thought of as the background
level of extinction.
Mass extinction - When numerous species become
extinct within a geologically short time interval.