Microevolution, or small-scale evolution within populations, was examined in Section 16.1.
Microevolution is the change in frequencies in a population.
The history of life on Earth is part of evolution.
The splitting of one species into two or more is called macroevolution.
Microevolutionary mechanisms that are at play within populations are also at play during macroevolution.
Microevolution and macroevolution are the result of the same processes at different scales.
Macroevolution is the result of microevolutionary change that leads to the formation of new species.
The species may become extinct after adapting to their environment.
Many of the species that have existed on Earth are no longer around.
The majority of mammals that experienced high levels of diversity in the past are now extinct.
Without the extinction of species, life on Earth wouldn't have the history found in the fossil record.
The "mystery of mysteries" was the focus of Darwin's life.
We take a closer look at what constitutes a species and how new species evolve.
There are a lot of different types of plants and animals in the forest.
Many of the organisms are different because of their appearance, even if you can't identify them.
An oak tree is different from a squirrel.
If you look a little closer, you can see that there are two different types of oak trees, one with large and small acorns, and the other with leaves of a slightly different shape.
Depending on which species definition is used, the oaks are either different species or variations of the same species.
Many types of evidence are used to define a species.
A taxonomist, a scientist who classifies organisms into groups, makes a hypothesis about whether they are different species based on the evidence, such as their external features.
Each species is a hypothesis about how the Earth's tree of life is organized.
New information can result in the redefinition of a species.
Linnaeus believed that birds and bats should be in the same group because they both have wings.
Birds and bats are different organisms on different branches of the tree of life.
All of the diversity of life on Earth has come from the evolution of new species.
We have defined a species as a type of living organisms, but in this chapter we describe them in more depth.
First, we look at the major species concepts, or the different ways in which a species can be defined, and then we look at some of the mechanisms by which new species originate.
Diagnostic traits are one or more distinct physical characteristics that distinguish a species from another.
Many of the species Linnaeus defined have held up to 200 years of scrutiny.
There are some disadvantages that Linnaeus could not have predicted.
There aren't many measurable traits forbacteria and other organisms.
There are similarities and differences between organisms.
The males of the leopard frog species in North America have a unique call that is difficult to distinguish in appearance.
The leopard frog was once considered to be a single species.
There are at least three frog species, the Rio Grande, southern, and northern leopard.
They are reproductively isolated because they each have a unique call for mates.
A way to define fossil species is through the use of the morphological species concept.
Fossils don't give information about color, the structure of soft tissues or behavioral characteristics.
There are subtle differences in skeletal features that can be used to diagnose differences between species.
The evolutionary species concept relies on identification to distinguish one species from another.
speciation was proposed to be explained in the fossil record.
The evolutionary species concept requires that the members of a species share an evolutionary pathway.
Small, transitional changes in a trait are not used to define new species because they are part of the same evolutionary pathway.
Changes in traits indicate the evolution of a new species in the fossil record.
These species can be recognized individually by differences in diagnostic traits, but they share an evolutionary pathway distinct from those of other whale species.
These species are only known from the fossil record.
The limbs would be included in such traits.
You and your cousins have a common grandmother.
Group of organisms have a common ancestor.
A species is the smallest set of interbreeding organisms that share a common ancestor.
The main criterion for defining a species is monophyly.
One advantage of the concept is that it doesn't rely only on appearance to define a species.
The individual A, C, G, or T nucleotide differences that are characteristic of a species can be compared to the region of the genome that has the A, C, G, or T sequence.
The species of microorganisms and cryptic species can be identified with the concept of the phylogenetic species.
One example is the giraffe, which has several regional populations distributed around Africa that are distinguishable only by a unique spot shape.
Each population should be recognized as an individual species because of the recent data showing that each region represents a monophyletic group.
There are now four confirmed giraffe species in Africa.
The brathe giraffe family tree is represented by a unique regional population.
Each of the branches is considered to be a giraffe species.
The biological species concept relies on reproductive isolation to identify different species.
Interbreeding is impeded by genetic processes.
If organisms cannot mate and produce offspring in nature or if their offspring are sterile, they are defined as different species.
The biological species concept can't be tested in nature because many potential species don't overlap in their distribution and thus don't have an opportunity to determine whether they are reproductively isolated.
The biological species concept can't be applied to reproducing living organisms.
The best indicator that two populations are following their own evolutionary pathways is the lack of gene flow.
A group of birds called the flycatchers all look the same, but they don't reproduce with one another.
Gene flow must not occur between the two species for them to remain separate.
Isolate mechanisms are reproductive barriers that prevent successful reproduction.
Before or after fertilization, reproductive isolation can occur.
Prezygotic isolation is before fertilization and postzygotic isolation is after fertilization.
When a spermfertilizes an egg, A is the first cell.
Should an offspring result in not being fertile, the postzygotic isolating mechanisms prevent it.
It is unlikely that fertilization will be successful if there are prezygotic isolating mechanisms.
There are various types of isolating mechanisms.
The primary goal of evolutionary biology is to infer the processes of evolution that produce the diversity seen in nature.
The evolutionary biologist is interested in explaining the differences between people.
The history of evolution among organisms is represented by the phylogeny, the most important tool of the evolutionary biologist.
Understanding how to interpret a phylogeny is fundamental to understanding how evolution works.
This guide will help you understand a phylogeny.
The origin of new species is called macroevolution.
All life on Earth is related to one another, according to Darwin's theory.
Evolutionary changes to existing species is what this means.
Both are governed by the same processes.
Different populations of a single species can accumulate genetic differences.
As more and more genetic differences accumulate, a population may no longer be able to recognize members of another population as potential mates.
The two populations are likely to be represented by two different groups.
The origin of a new species would be supported by the two concepts.
The common ancestor of all the species is represented by the node.
A taxon that is represented in the fossil record, but is now extinct, is represented by a shortened branch that is correlated with the time at which the extinction occurred.
A family tree is a hypothesis of evolutionary history of taxa.
There are many parts to a phylogeny, each of which tells us something about evolutionary relationships among taxa.
The species "A" is more closely related to "B" than to "C" because they share a more recent common ancestor.
Microevolution takes place at the level of the population.
Microevolution and macroevolution are governed by the same processes, but at different scales.
Microevolutionary change in a population leads to speciation.
Microevolution can result in the divergence of a population to form a new species.
The extinction of populations and species is one of the outcomes of evolution.
Page 301 habitats are less likely to meet and attempt to reproduce.
Flycatchers don't mate because of this.
In tropical rain forests, many animal species are restricted to a specific level of the forest canopy and isolated from similar species.
Several related species can live in the same locale, but if each reproduces at a different time of year, they don't attempt to mate.
The species are separate because of the different periods of peak mating activity.
Frogs can be found in ponds on the ground or in the water.
Different dispersal times help prevent fertilization of the gametes.
The species are separated due to breeding peaks at different times of the year.
Many animal species allow males and females to recognize each other.
Female crickets recognize male crickets by their chirps and male fireflies by their flashings.
Chemical signals called pheromones are used by many males to recognize females.
Female gypsies release pheromones that are detected miles away by male gypsies.
The blue-footed boobies of the Galapagos Islands can choose a mate through an elaborate display.
The male shows off his bright blue color by lifting up his feet.
reproduction can't occur if animal genitalia and plant floral structures are incompatible.
Cross-fertilization in plants can be prevented by inaccessibility of pollen.
The genitalia of many insect species are not compatible with those of the members of other species.
Male dragonflies have claspers that can be used to hold only females of their species.
If the gametes of two different species meet, they may not become a zygote.
In animals, the sperm of one species may not be able to survive in the reproductive tract of another species, or the egg may have only one species' sperm in it.
Only certain types of pollen grains can grow in plants, so that sperm can reach the egg.
The mechanisms prevent hybrid offspring from reproducing.
It is often infertile if a hybrid is born.
The genes of the parents can't be passed on to the next generation.
Mules are infertile.
Both horses and donkeys can't produce gametes.
A hybrid is not viable.
A zygote may fail to develop because it has two different sets of chromosomes.
The embryo may not develop properly if it gets incompatible instructions from the maternal and paternal genes.
There is a chance that the hybrid zygote will become a sterile adult.
A cross between a female horse and a male donkey causes an inability to produce viable gametes.
A cross between a cabbage and a radish can produce offspring that can't form gametes, most likely because the cabbage chromosomes and the radish chromosomes can't align during meiosis.