Chapter 9: Evolution and Diversity

Species

A group of living organisms consisting of similar individuals capable of exchanging genes or interbreeding. The species is the principal natural taxonomic unit, ranking below a genus and denoted by a Latin binomial, e.g., Homo sapiens.

Homologous structures

A homologous structure is an example of an organ or bone that appears in different animals, underlining anatomical commonalities demonstrating descent from a common ancestor. In other words, it's when very different animals have bones that appear very similar in form or function and seem to be related.

Heterotroph Hypothesis

According to the heterotrophic hypothesis for the origin of life, early organisms depended on abiotically synthesized organic molecules for their structural components and as an energy source.

B. Kingdom Plantae

All plants are multicellular, eukaryotic, and photosynthetic (i.e., autotrophs) and have a cell wall made of cellulose. Note also that plant biologists use the term division instead of phylum; however, the two terms are essentially synonymous. Plants are grouped into two general categories based on how they transport water: the nonvascular plants and the vascular plants. Vascular plants are further subdivided into seedless plants and seed plants. Seed plants are further divided into nonflowering plants (gymnosperms) and flowering plants (angiosperms).

1) Phylum Rhizopoda (Amoebas)

Amoebas are all unicellular and move about using cellular extensions called pseudopodia. They are found in soils and also in freshwater and marine environments. Some are parasitic, such as those what cause amoebic dysentery in humans.

D. Kingdom Animalia

Animals are eukaryotic, multicellular, and heterotrophic. This is the most diverse of the six kingdoms. You should definitely know the characteristics of each of the following phyla (but again, don't worry too much about the official names).

3) Phylum Platyhelminthes (Flatworms)

Animals in this group exhibit bilateral symmetry and moderate cephalization (a head). They include planaria (nonparasitic), flukes, and tapeworms (both parasitic).

FITNESS

Another way of saying that an organism is a better competitor is to say that the organism is more "fit." Fitness describes an organism's ability to contribute to the next generation's gene pool by producing surviving offspring.

III. Domain Eukarya

As its name implies, this domain is made up of eukaryotes. All eukaryotes contain nuclei, membrane-bound organelles, and linear DNA. They are divided into four main kingdoms, the characteristics of which are described on the next page.

EVOLUTION

As you know, evolution can be described as a change in population over time. Interestingly, the driving force of evolution, natural selection, operates on the level of the individual. In other words, evolution is defined in terms of populations but occurs in terms of individuals.

e) Class Aves (Birds)

Birds are tetrapods with the forelimbs modified as wings. They breathe through lungs and lay shelled eggs. They are endothermic. Examples are owls, eagles, sparrows, and penguins.

Genetic Variability and Evolution

Changes in gene pools can occur through random mutation, as we've seen previously, but it can take a long time for this to have a significant effect on the population. More rapid changes in gene pools are caused by competition. More specifically, because of mutations, genetic variability exists. Because of genetic variability (different genotypes), there is physical variability (different phenotypes). And because of physical variability, some members of a population are better equipped to interact with their environment; in other words, they are better competitors.

8) Phylum Chordata (Chordates)

Chordates have a hollow notochord, a dorsal nerve cord, pharyngeal gill slits, and a tail (at some point in their development). Almost all are vertebrates. Chordates include fish, amphibians, reptiles, birds, and mammals.

"survival of the fittest"

Darwin concluded that it was impossible for the finches and tortoises of the Galapagos to simply "grow" longer beaks or necks. Rather, the driving force of evolution must have been natural selection. Quite simply put, this means that nature would "choose" which organisms survive on the basis of their fitness. For example, on the first island Darwin studied, there must once have been short-necked tortoises. Unable to reach higher vegetation, these tortoises eventually died off, leaving only the tortoises with longer necks. Consequently, evolution has come to be thought of as "survival of the fittest": Only those organisms most fit to survive will survive.

Charles Darwin

Darwin was a nineteenth-century British naturalist who sailed the world in a ship named the HMS Beagle. Darwin developed his theory of evolution based on natural selection after studying animals in the Galapagos Islands and other places.

4b) Class Dicots

Dicots have two seed leaves (two cotyledons), netlike veins in their leaves, flower parts in multiples of four or five, vascular tissue arranged in a ring, and a taproot system.

Divergent Evolution

Divergent evolution is the process by which two populations of the same species end up having different behaviors and traits. They used to have similar traits, but as a result of a changing environment they changed and over time their behaviors and traits were no longer similar; in other words, they diverged.

Cyanobacteria

Domain Bacteria has one kingdom, which is called Eubacteria. This domain (and kingdom) includes the Cyanobacteria, which are also known as blue-green algae. The Cyanobacteria contain chlorophyll and can photosynthesize.

PHYLOGENY ORDER

Domain • Kingdom • Phylum • Class • Order • Family • Genus • Species Dumb King Phillip Came Over From Germany—So? Less in common ---> More in common

These early cells were anaerobic organisms.

Earth's early atmosphere contained little or no oxygen, but oxygen was a waste product of the early autotrophs, and gradually it accumulated. As the heterotrophs and autotrophs evolved, they learned how to use this oxygen to produce energy more efficiently. Eventually over millions of years, the oxygen-using organisms came to be the dominant organisms on the planet.

SUMMARY

Evolution is a change in a population's gene pool. It happens because • genetic variability allows some individuals to be better competitors than others. In the "game" of natural selection, they win; • the winners survive, reproduce, and pass their genes on to their offspring; • the offspring have genes like those of their parents. Hence, the gene pool changes. With each generation, it has more and more of the alleles that come from the better competitors.

An easy way to remember the order in which phylum Chordata evolved is to remember the word "FARM," but with a "B" stuck in the middle of it—"FARBM."

F: Fish A: Amphibians R: Reptiles B: Birds M: Mammals

2) Division Pterophyta (Ferns)

Ferns are some of the earliest vascular plants and contain the vascular tissue xylem and phloem, as well as true stems, leaves, and roots. They do NOT, however, have seeds. Instead, ferns have spores, which can be scattered by wind.

C. Kingdom Fungi

Fungi are all eukaryotic, almost all are multicellular, and they have a cell wall made of chitin. One exception is yeast, which is a unicellular fungus. Most fungi have a filamentous structure and are multinucleate. They lack chloroplasts and are therefore heterotrophic (cannot produce their own food). They lack a digestive system and are absorptive feeders. Absorptive feeding is the process of taking up small organic molecules from the environment. Because they often live on decaying material, they are classified as decomposers.

Carolus Linnaeus

He came up with what is known as the modern system of classification, called the binomial system.

convergent evolution

In evolutionary biology, convergent evolution is the process whereby organisms not closely related (not monophyletic), independently evolve similar traits as a result of having to adapt to similar environments or ecological niches.

Analogous structures

In evolutionary biology, the term analogous structures pertain to the various structures in different species having the same function but have evolved separately, thus do not share common ancestor. ... Examples of analogous structures are as follows: wings of insects and birds used for flying.

What's in a Name

It might be helpful to remember that a name ending in -phyta refers to plants and one ending in -mycota refers to fungi.

When did life appear?

Life first appeared on this planet around one billion years ago.

f) Class Mammalia (Mammals)

Mammals are endothermic, have hair, and nourish their young from mammary glands. They breathe through lungs. Most bear live young. Examples are rodents, kangaroos, antelope, and humans.

EXPERIMENTATION

Many scientists have conducted experiments in which they simulated the gaseous conditions of early Earth's atmosphere in a flask. Sparks of electricity were discharged into the gases to mimic lightning, and it was found that under these artificial conditions, amino acids and other building blocks of life (like RNA) formed spontaneously. You already know how important nucleic acids and proteins are to living organisms, so you can probably imagine that these early proteins and nucleic acids may have run chemical reactions and may have had the ability to replicate themselves. Eventually, the first cells were born. They were heterotrophs, meaning that they could not synthesize their own food.

4) Phylum Mollusca (Mollusks)

Mollusks are soft-bodied animals with hard external shells, such as snails, oysters, and clams. Exceptions are octopi and squid, which have only reduced, internal shells. Mollusks have three major body regions: a foot for movement; a visceral mass, where organs are contained; and amantle, which may secrete a shell.

4a) Class Monocots

Monocots are named for their single-seed leaves (mono = one) called cotyledons. Other characteristics of monocots include parallel veins in their leaves, flower parts in multiples of threes, a complex arrangement of vascular tissue in their stems, and a fibrous root system.

Natural Selection

Natural selection, process that results in the adaptation of an organism to its environment by means of selectively reproducing changes in its genotype, or genetic constitution.

geographic isolation

New species may form when a group of individuals remains isolated from the rest of the species.

A. Kingdom Protista

Protists are eukaryotes and contain organelles and a true nucleus. Most are unicellular, but some form colonies, and some are truly multicellular (algae). This kingdom can be divided into three main groups, or phyla protozoa (animal-like protists), algae (plant-like protists)—except for cyanobacteria, the blue-green algae—and a few fungus-like protists. When you study these phyla, don't get too concerned about learning the "official" names. Most questions on the exam will refer to these organisms using their more common names, shown here in parentheses.

d) Class Reptilia (Reptiles)

Reptiles are terrestrial animals with thick, scaly skin adapted to resist water loss. They live well in dry areas, although some inhabit water. Their eggs have shells to resist dehydration, or they bear live young. They breathe through lungs. Examples are crocodiles, lizards, and snakes.

Evolution of Autotrophs

Soon, food became scarce. In other words, the heterotrophs required nutrients at a faster rate than they were being formed spontaneously. This led to the evolution of autotrophs, organisms that could make their own food using solar energy.

1) Phylum Porifera (Sponges)

Sponges are sessile (nonmoving) animals. They have a perforated body wall made of two layers of cells. Water is drawn through the body wall into the animal, where food in the water is trapped and ingested. Most sponges live in marine environments.

2) Phylum Apicomplexa (Sporozoans)

Sporozoans are all animal parasites. Some cause serious human diseases such as malaria, caused by the parasite plasmodium. Most members of this phylum have life cycles with both sexual and asexual stages that often require two or more different host species for completion. For example, plasmodium requires both humans and mosquitoes to complete its life cycle.

Vestigial Structures

Structures that have no apparent function and appear to be residual parts from a past ancestor are called vestigial structures. Examples of vestigial structures include the human appendix, the pelvic bone of a snake, and the wings of flightless birds.

Taxonomy

Taxonomy is the fancy term given to the science of classification and naming.

How does genetic variability happen?

The answer is the random mutation of DNA. DNA mutation is the basis for genetic variability. DNA mutation simply means that an error was made during DNA replication.

Atmospheric Differences

The atmosphere then was very different from what it is today. Today's atmosphere is mostly nitrogen (about 78%), oxygen (about 21%), and small amounts of carbon dioxide, helium, and neon. The atmosphere on early Earth, however, was mostly made up of hydrogen, ammonia, methane, and water.

The binomial system of classification

The binomial system of classification is based on a two-part name for each organism. The first part is the organism's genus, and the second part is the organism's species. The genus is capitalized, but the species is not. Both words are italicized.

The climate of early Earth

The climate of early Earth was fairly intense; there was more lightning, volcanic activity, and UV radiation than we experience today.

Speciation

The formation of new and distinct species in the course of evolution.

The Fossil Record

The fossil record gives evidence about the history of life on our planet. This record of past life also shows how different groups of organisms have changed over time. This is evidence for evolution.

Gene Pool

The stock of different genes in an interbreeding population.

genetic variability

The tendency of individual genetic characteristics in a population to vary from one another.

c) Class Amphibia (Amphibians)

These animals are well adapted to both land and water. Their eggs lack shells and must be laid in the water. They have an aquatic larval stage and undergo a metamorphosis into a terrestrial adult. They breathe through lungs and/or skin. Examples are frogs and salamanders.

5) Phylum Annelida (Segmented Worms)

These animals have a closed circulation and a mouth and anus, and they excrete waste through metanephridia. The best example is the earthworm; this group also includes leeches.

2) Phylum Cnidaria (Coelenterates)

These animals have body walls made of two layers of cells and a central, saclike digestive system. They exhibit radial symmetry. Examples are hydra, jellyfish, and sea anemones.

3) Division Coniferophyta (Conifers)

These are true vascular plants. The term conifer refers to the cones that carry the seeds of these plants. Most are large evergreen trees, such as pines, firs, and cedars. Because the seeds are not protected in a seed coat, these are "naked-seed" plants, or gymnosperms. Gymnosperms do NOT produce flowers.

5) Phylum Euglenophyta (Euglena)

These are unicellular, photosynthetic algae. They move with a flagellum (a whiplike tail).

a) Class Chondrichthyes (Cartilaginous Fishes)

These fish have flexible skeletons made of cartilage instead of bone and well-developed jaws and fins. They breathe through gills. Some lay eggs and some bear live young. Examples are sharks and sting rays.

b) Class Osteichthyes (Bony Fishes)

These fish have true bone skeletons. They breathe through gills and lay large numbers of eggs, which lack shells. They live in both freshwater and marine environments. Examples are bass, tuna, and trout.

7) Phylum Phaeophyta (Brown Algae)

These organisms are commonly known as seaweeds and are the largest and most complex of the plantlike protists. All are multicellular and most live in marine environments. Some are very large, such as the giant kelp.

4) Phyla Myxomycota and Acrasiomycota (Slime Molds)

These organisms resemble an overgrown amoeba. They contain many nuclei.

7) Phylum Echinodermata (Echinoderms)

These slow-moving or sessile animals exhibit radial symmetry and spiny exoskeletons (echinoderm means "spiny skin"). They have a water vascular system ending in tube feet that function in feeding, gas exchange, and movement. Examples are sea stars, sea urchins, and sand dollars.

6) Phylum Bacilariophyta (Diatoms)

These unicellular organisms have unique glasslike walls and live in both freshwater and marine environments. These walls remain behind when the organism dies and form the sediments known as diatomaceous earths. Diatomaceous earth is useful as a filtering medium. Diatoms make up an important part of the marine food chain and are the most important producers in phytoplankton.

II. Domain Archaea

This domain is also made up of prokaryotes, in the kingdom Archaebacteria. Like Domain Bacteria prokaryotes, Archaebacteria lack nuclei and organelles, and have a circular DNA genome; however, they also have some features in common with eukaryotes (such as multiple types of RNA polymerase and methionine as the initiator amino acid, just to name a couple). Domain Archaea organisms often live in extremely harsh environments that most other organisms could not tolerate; for this reason they are described as "extremophiles" (think of them as the X-Games enthusiasts of the living world). They include the extreme halophiles (that live in extremely salty conditions), the extreme thermophiles (that live in extremely hot conditions), and the methanogens (extreme anaerobes that release methane gas as a waste product).

I. Domain Bacteria

This domain is made up of prokaryotes and includes the bacteria most people are familiar with, from harmful disease-causing organisms (like E. coli) to the beneficial bacteria used to make yogurt and cheese. They lack a nucleus and any membrane-bound organelles (they have ribosomes, which are not bounded by membranes), and have a circular DNA genome.

2) Division Basidiomycota (Club Fungi)

This group consists of about 25,000 members, including mushrooms, shelf fungi, and puffballs. Some are edible.

4) Division Anthophyta (Flowering Plants)

This group consists of true vascular plants that produce flowers and pollen. Their seeds are protected by fruits and nuts. Examples are apples, lima beans, tomatoes, melons, etc.

1) Division Bryophyta (Nonvascular Plants)

This group lacks the vascular tissue found in most plants, called xylem and phloem. Therefore they must live in damp areas where water is abundant. Furthermore, they require water for fertilization. These plants do NOT have true stems, leaves, and roots. Examples are mosses, liverworts, and hornworts.

1) Division Zygomycota

This group of fungi reproduces sexually and includes common molds as well as mycorrhizae (mutualistic associations between plant roots and fungi).

3) Phylum Ciliophora (Ciliates)

This group of unicellular organisms is characterized by their use of cilia for movement and feeding. An example is paramecium.

6) Phylum Arthropoda (Arthropods)

This is the most diverse phylum in the animal kingdom, with nearly one million different species and more than 1018 (one billion billion) members. Arthropods have jointed appendages, a hard exoskeleton containing chitin, and a segmented body with a head, thorax, and abdomen. They have an open circulatory system and eliminate wastes through Malpighian tubules. Arthropods include crustaceans (e.g., crabs), insects (e.g., moths, ants), and arachnids (e.g., spiders). This is the largest and most diverse phylum.

Remember

Today's atmosphere contains mostly nitrogen and oxygen, and the primary organisms on the planet are aerobic. Earth's early atmosphere DID NOT contain oxygen. It contained mostly hydrogen, ammonia, methane, and water, and the primary organisms at that time were anaerobic.

Phylogeny

When we say that organisms have things in common, what we mean is that different organisms came from common ancestors, and they share some traits from those ancestors of long ago. Scientists classify organisms based on their evolutionary relationships (phylogeny).

OTHER sources of variations

independent assortment of chromosomes, crossing over during meiosis, random fertilization These all help pass on the mutations that occur.

Look at the organizational scheme and realize:

• Each domain is made up of one or more kingdoms. • Each kingdom is made up of many phyla. • Each phylum is made up of many classes. • Each class is made up of many orders. • Each order is made up of many families. • Each family is made up of many genera (plural of genus). • Each genus is made up of many species.

Darwin elaborated his theory in a book titled On the Origin of the Species. In a nutshell, here's what Darwin observed:

• Each species produces more offspring than can survive. • These offspring compete with one another for the limited resources available to them. • Organisms in every population vary. • The offspring with the most favorable traits or variations are the most likely to survive and therefore produce offspring.

Realize also that:

• Organisms of the same species have more in common than do organisms simply belonging to the same genus. • Organisms of the same genus have more in common than do organisms simply belonging to the same family. • Organisms of the same family have more in common than do organisms simply belonging to the same order. • Organisms of the same order have more in common than do organisms simply belonging to the same class. • Organisms of the same class have more in common than do organisms simply belonging to the same phylum. • Organisms of the same phylum have more in common than do organisms simply belonging to the same kingdom. • Organisms of the same kingdom have more in common than do organisms simply belonging to the same domain.