Create an account
about 2,500 years ago, the Greek philosopher promoted the idea that life arose in water and that simpler forms of life preceded more complex ones.
whose views had an enormous impact on Western culture, generally held that species are fixed, or permanent, and do evolve.
supported the view that variations noted among members of the same species were due to imperfection. Therefore, only one representation represented the perfect model of a particular species.
a French naturalist known as the Father of Paleontology (the study of fossils). His views supported catastrophism.
points to gaps in the fossil record being the result of catastrophic events that would cause the extinction of specie(s). In turn, God would create a new species that was similar to the original. (Cuvier)
suggested that Earth might be much older than 6,000 years. He also observed some telling similarities between specific fossils and certain living animals. In 1766, Buffon proposed the possibility that a species represented by a particular fossil form could be an ancient version of a group of similar living species.
Inheritance of Acquired Characteristics; In the early 1800s, French naturalist Jean-Baptiste Lamarck suggested that the best explanation for this relationship of fossils to current organisms is that life evolves. Lamarck explained evolution as a process of adaptation, the refinement of characteristics that equip organisms to perform successfully in their environments. Unfairly, we remember Lamarck today mainly for his erroneous view of how adaptations evolve. He proposed that by using or not using its body parts, an individual develops certain characteristics, which it passes on to its offspring. However, you should remember from your introductory biology course that at the time of conception a child receives all of its genetic composition. Any physical changes that occur after birth are not passed on to the nest generation.
Inheritance of Acquired Characteristics example
if the Roc (at the time he was wrestling) conceived a child with China (female wrestler) the child would not automatically have the physical attributes of its parents. Students often misunderstand the basic process of evolution and reflect, instead, a Lamarckian point of view. Organisms do not evolve structures because of want or need. Evolution is a passive process in which the environment favors diversity that exists within a population. Adaptations evolve in populations of organisms. Organisms do not evolve adaptations
The Origin of Species
Darwin's book drew a cohesive picture of life. The Origin of Species focused biologists' attention on the great diversity of organisms—their origins and relationships, their similarities and differences, their geographic distribution, and their adaptations to surrounding environments.
The voyage of the HMS Beagle (1831-1836)
As a boy, Darwin was interested in nature. The Beagles was a tour that would have a profound effect on Darwin's thinking and eventually on the thinking of the entire world. Darwin was 22 years old when he sailed from Great Britain with the Beagle in December 1831. The main mission of the voyage was to chart poorly known stretches of the South American coastline. While the crew of the ship surveyed the coast, Darwin spent most of his time on shore, observing and collecting thousands of specimens of the native plants and animals of South America. As the ship worked its way around the continent, Darwin observed the various adaptations of organisms that inhabited such diverse environments as the Brazilian jungles, the grasslands of the Argentine pampas, the desolate and frigid lands of Tierra del Fuego near Antarctica, and the towering heights of the Andes. Darwin noticed that: (a) the plants and animals living in temperate regions of South America seemed more closely related to species living in tropical regions of that continent than to species living in temperate regions of Europe, and (b) the South American fossils Darwin found were distinctly South American in their resemblance to the living plants and animals of that continent.
named after the giant tortoises found there. These are relatively young volcanic islands about 900 kilometers (540 miles) off the Pacific coast of South America. Most of the animals of the Galápagos live nowhere else in the world but resemble species living on the South American mainland. It is as though plants and animals that strayed from the mainland and then diversified as they adapted to environments on the different islands had colonized the islands. Among the birds Darwin collected on the Galápagos were several types of finches. Some were unique to individual islands, while others were distributed on two or more islands that were close together. Darwin did not appreciate the full significance of the finches he collected until years after returning to Britain. Since then, biologists have applied modern methods of comparing species to reconstruct the evolutionary history of Darwin's finches.
Principles of Geology
by Scottish geologist Charles Lyell. (one of two books that played a pivotal role in Darwin's thought process) The book presented the case for an ancient Earth sculpted by gradual geological processes that continue today.
First, Earth must be very old if it has been shaped by such slow processes as mountain building and erosion. Second, the new geology explained how slow and subtle processes occurring over vast tracts of time could cause enormous change. Darwin would eventually apply this principle of gradualism to the evolution of Earth's life.
wrote an Essay on the Principles of Population. In this work he argues that death due to calamity, disease or predation is a necessary evil as means of population control. He proposed that death and famine were inevitable because the human population tends to increase faster than the supply of food.
(considered the cofounder of the theory of natural selection), a British naturalist doing fieldwork in Indonesia, developed a concept of natural selection identical to Darwin's.
With the publication in 1859 of The Origin of Species, Darwin presented the world with
an avalanche of evidence and a strong, logical argument for evolution and natural selection as the mechanism of descent with modification. Two main points- First, he argued from evidence that the species of organisms inhabiting Earth today descended from ancestral species. Second, his argument for natural selection as the mechanism for descent with modification.
is that a population of organisms can change over the generations if individuals having certain heritable traits leave more offspring than other individuals and that those offspring survive long enough to also reproduce. The result of natural selection is evolutionary adaptation, a population's increase in the frequency of traits that are suited to the environment. In modern terms, we would say that the genetic composition of the population had changed over time, and that is one way of defining evolution. We can also use the term evolution on a much grander scale to mean all of biological history, from the earliest microbes to the enormous diversity of modern organisms.
are the preserved remnants or impressions left by organisms that lived in the past. Most fossils are found in sedimentary rocks.
is this ordered array in which fossils appear in the rock layers that mark the passing of geological time.
The oldest known fossils
date from about 3.5 billion years ago and are prokaryotes (bacteria and archaea). Fossils in younger layers of rock chronicle the evolution of various groups of eukaryotic organisms. Fishlike fossils are the oldest vertebrates in the fossil record. Amphibians are next, followed by reptiles, then mammals, and birds.
study fossils and have discovered many transitional forms that link past and present. For example- a series of fossils documents the changes in skull shape and size that occurred as mammals evolved from reptiles. Another example is a series of fossilized whales that connect these aquatic mammals to their land-dwelling predecessors.
The comparison of body structures between different species is called comparative anatomy. Certain anatomical similarities among species bear witness to evolutionary history. For example, the same skeletal elements make up the forelimbs of humans, cats, whales, and bats, all of which are mammals. The functions of these forelimbs differ. If these limbs had been uniquely engineered, we would expect that their basic designs would be very different. However, structural similarity would not be surprising if all mammals descended from a common ancestor with the prototype forelimb.
descent with modification
Ancestral structures that originally functioned in one capacity become modified as they take on new functions.
The comparison of structures that appear during the development of different organisms is called comparative embryology.
Evolutionary relationships among species leave signs in DNA and proteins—in genes and gene products. If two species have libraries of genes and proteins with sequences of monomers that match closely, the sequences must have been copied from a common ancestor. Darwin's boldest hypothesis was that all forms of life are related to some extent to the earliest organisms through branching evolution. The molecular signs include a common genetic code shared by all species.
Darwin's Theory of Natural Selection
Darwin synthesized his theory of natural selection from two key observations. First, that all species tend to produce excessive numbers of offspring. (1) Natural resources are limited. (2) The production of more individuals than the environment can support leads to a struggle for existence among the individuals of a population. (3) In most cases, only a small percentage of offspring will survive in each generation. Second, individual variation abounds in almost all species and much of this variation is heritable.
From these two observations, Darwin arrived at the conclusion that defines natural selection
Individuals whose inherited traits are best suited to the local environment are more likely to survive and reproduce than less fit individuals. In other words, the individuals that function best in the local environment tend to leave the most offspring. The environment screens a population's inherent variability. Differential success in reproduction causes the favored traits to accumulate in the population over the generations.
Environment and Natural Selection
You must understand that the environment does the selecting in natural selection. Species don't evolve because of need. Biological diversity exists and the environment selects. Evolution is not deliberate, it is reactive. For example: ―Birds evolved wings seems as if birds did something deliberately. ―Wings evolved in birds is more accurate, in that something was done to birds in the process.
is a group of individuals of the same species living in the same area at the same time. One population may be isolated from others of the same species. One population center may blur into another in a region of overlap where members of both populations are present but less numerous. Individuals are more concentrated in the population centers, and they are likely to breed with other locals. A population is the smallest biological unit that can evolve. A common misconception is that individual organisms evolve, in the Darwinian sense, during their lifetimes. The evolutionary impact of natural selection is only apparent in tracking how a population changes over time.
emphasizes the extensive genetic variation within populations and (2) tracks the genetic makeup of populations over time.
Genetic Variation in Populations
Individual variation abounds in populations of all species that reproduce sexually. Most populations have a great deal of variation that can be detected only by biochemical means, such as ABO blood groups in humans.
Not all variation in a population is heritable
Phenotype results from a combination of the genotype, which is inherited, and the many environmental influences. Only the genetic component of variation is relevant to natural selection.
two or more morphs are present in readily noticeable numbers—that is, if neither morph is extremely rare.
Sources of Genetic Variation
Mutations and sexual recombination, which are both random processes, produce genetic variation
The gene pool
consists of all alleles (alternative forms of genes) in all the individuals making up a population.
which is an inherited inability to break down the amino acid phenylalanine. If untreated, the disorder causes severe mental retardation. PKU is due to a recessive allele.
Hardy- Weinberg equilibrium
A nonevolving population is in genetic equilibrium. The population's gene pool remains constant over time. (1) The frequencies of alleles and genotypes are unchanged. (2) Sexual shuffling of genes cannot by itself change a gene pool.
causes of microevolution are
genetic drift, (Founder Effect and Bottleneck Effect), gene flow, mutation, and natural selection.
This evolutionary mechanism, a change in the gene pool of a small population due to chance
The Bottleneck Effect
Disasters such as earthquakes, floods, droughts, and fires may reduce the size of a population drastically. The small surviving population may not be representative of the original population's gene pool. Certain alleles will be overrepresented, some underrepresented, and some eliminated. Bottlenecking usually reduces the overall genetic variability in a population because at least some alleles are likely to be lost from the gene pool. An important application of this concept is the potential loss of individual variation, and hence adaptability, in bottlenecked populations of endangered species. The loss of genetic diversity in a population because of the bottleneck effect is a significant problem in conservation. When a species is reduced to relatively few individuals and then is brought back to abundance by extraordinary efforts, the species is not fully recovered. The lost genetic diversity may be a prerequisite for the long-term survival of the species.
may continue to change the gene pool for many generations until it grows large enough for sampling errors to be insignificant.
The Founder Effect
Genetic drift is also likely when a few individuals colonize an island, lake, or some other isolated habitat. The smaller the colony, the less its genetic makeup will represent the gene pool of the larger population from which the colonists emigrated. It undoubtedly contributed to the evolution of organisms that arrived on the Galápagos Islands. Consider that you and all the students present in today's class are the only survivors of some global catastrophe. Would your class adequately represent the biological diversity of the current human population?
a population may gain or lose alleles by gene flow, the genetic exchange with another population. Gene flow occurs when fertile individuals or gametes migrate between populations. Gene flow tends to reduce genetic differences between populations. Extensive gene flow can amalgamate neighboring populations into a single population with a common gene pool. As humans began to move about the world more freely, gene flow became an important agent of microevolution in populations that were previously isolated.
Reproductive success is generally subtle and passive. Darwinian fitness is the contribution an individual makes to the gene pool of the next generation relative to the contributions of other individuals. Production of fertile offspring that then reproduce is the only score that counts in natural selection.
shifts the phenotypic ―curve of a population by selecting in favor of some extreme phenotype. For example, directional selection might favor the darkest mice or pesticide resistance in insects.
maintains variation for a particular trait within a narrow range, works by selecting against the more extreme phenotypes, and typically occurs in relatively stable environments.
the rock deposited at the time of the dinosaurs contains a thin layer of clay rich in, an element very rare on Earth but common in meteorites. Many paleontologists conclude that the iridium layer is the result of fallout from a huge cloud of dust formed when a large meteorite or asteroid hit Earth. The cloud would have blocked light and disturbed climate severely for months, perhaps killing off many plant species.
The impact hypothesis
predicts that we should find a huge impact crater of the right age. In 1981, two petroleum geologists discovered the Chicxulub crater near the Yucatán Peninsula in the Caribbean Sea. This 150-300 kilometers wide impact site dates to the predicted time, was created when a meteorite or asteroid the size of San Francisco slammed into the Earth, and would have released thousands of times more energy than the world's combined stockpile of nuclear weapons.
Macroevolution includes 4 major things
the multiplication of species; the origin of evolutionary novelty, such as the wings and feathers of birds and big brains in humans; the explosive diversification that follows some evolutionary breakthrough—such as the origin of thousands of plant species after the flower evolved; and mass extinctions.
occurs when a population may change so much through adaptation to a changing environment that we call it a new species.
is a Latin wording meaning "kind" or "appearance." A population or group of populations whose members have the potential to interbreed with one another in nature to produce fertile offspring, but who cannot successfully interbreed with members of other species.
1927, led an expedition to New Guinea and identified 138 species of birds on the basis of differences in their appearance. The local tribe of Papuan natives had given names of their own to 137 bird species. Mayr defines species based upon the biological species concept.
The biological species concept
species as "groups of interbreeding natural populations that are reproductively isolated from other such groups" (in Mayr's words). The biological species concept does not account for organism that reproduce asexually.
blocks exchange of genes between species and keeps their gene pools separate.
impede mating between species or hinder fertilization of eggs if members of different species should attempt to mate. Such barriers may involve one or more of the following mechanisms of isolation
are back-up mechanisms that operate should interspecies mating actually occur and form hybrid zygotes.
offspring are infertile. A mule is the hybrid offspring of a female horse and a male donkey. Mules are sterile. Mules are one exception to the hybrids that are often produced this way because they are strong. Often these hybrids may be weak and have many genetic abnormalities
the initial block to gene flow is a geographical barrier that physically isolates the splinter population. Allopatric speciation is more likely when a population is small and isolated. Speciation occurs only with the evolution of reproductive barriers between the isolated population and its parent population. ie. creeping glacier, land bridge.
is the origin of a new species, without geographic isolation, in the midst of the parent population. A genetic change can produce a reproductive barrier between mutants and the parent population. Sympatric speciation is not widespread among animals but may account for over 25% of all plant species.
Many plant species have originated from accidents during cell division that resulted in extra sets of chromosomes producing polyploids. Tetraploid species may evolve in a single generation without geographic isolation. Most polyploid species arise from the hybridization of two parent species.
Under the microevolution theory, traditional evolutionary trees sprout branches that diverge gradually. New species are an accumulation of many smaller changes occurring over vast spans of time. Darwin- "Although each species must have passed through numerous transitional stages, it is probable that the periods during which each underwent modification, though many and long as measured by years, have been short in comparison with the periods during which each remained in an unchanged condition."
The punctuated equilibrium model
suggests that species diverge in spurts of relatively rapid change, instead of slowly and gradually. The term punctuated equilibrium is derived from the idea of long periods of stasis (equilibrium) punctuated by episodes of speciation.
is the retention of juvenile body features in the adult (from the Greek paedos, "child," and morphosis, "shaping"). Paedomorphosis is an example of such a dramatic shift in development. A salamander called an axolotl grows to full size and reproduces without losing its external gills, a juvenile feature in most species of salamanders. This albino axolotl salamander illustrates paedomorphosis. Paedomorphosis has also been important in human evolution. Humans and chimpanzees are much more alike as fetuses than they are as adults. As fetuses, they share certain features: rounded skulls, small jaws, and a flat and rounded face. The adult human skull retains fetal features even after we are mature. The human brain is proportionately larger than the chimpanzee brain because growth of the organ is switched off much later in human development.
(1) the Precambrian,= the longest era (2) Paleozoic, (3) Mesozoic, and (4) Cenozoic eras. The boundaries are marked in the fossil record by explosive diversification of many new forms of life and mass extinctions.
The most common method to determine the ages of fossils in years. This method is based on the decay of radioactive isotopes.
About 250 million years ago, near the end of the Paleozoic era, plate movements brought all the landmasses together into the supercontinent named Pangaea, meaning "all land." Many habitats were dramatically changed, and biological diversity was reshaped. Species that had been evolving in isolation came together and competed. The total amount of shoreline was reduced. Ocean basins increased in depth, which lowered the sea level and drained the shallow coastal seas. Ocean currents changed. About 180 million years ago (during the Mesozoic era), Pangaea began to break up, causing geographical isolation of colossal proportions.
The Permian extinctions
at about the time Pangaea formed, claimed over 90% of the species of marine animals and took a tremendous toll on terrestrial life. (largest extinction). Each massive dip in species diversity has been followed by explosive diversification of certain survivors.
Mammals existed for at least 75 million years before
undergoing an explosive increase in diversity just after the Cretaceous.
(1707-1778), a Swedish physician and botanist (plant specialist), started the taxonomic system with binomial names and a hierarchical classification.
(1) The first, the genus, is capitalized. (2) The second refers to one species within the genus, in lowercase.
may look and function very differently in separate species, but they evolved from the same structure and a common ancestor. Examples include a whale limb and a bat wing. The greater the number of homologous structures between two species, the more closely the species are related. Not all likeness is inherited from a common ancestor: Similar evolutionary pressures acting on unrelated species may produce similar, or analogous, structures. Homologous structures are used to develop phylogenetic trees and classify organisms according to evolutionary history.
Species from different evolutionary branches may have analogous but not homologous structures. Similarity due to convergence is termed analogy, not homology. Wings of an insect and wings of a bird are analogous but not homologous.
Kingdoms Plantae, Fungi, and Animalia
consist of multicellular eukaryotes that differ in structure, development, and modes of nutrition.
contains: all eukaryotes that do not fit the definitions of plants, fungi, or animals and certain large, multicellular organisms that are believed to be direct descendants of unicellular protists.
as one alternative to the five- kingdom system. The three domains include (1) two domains of prokaryotes, the Bacteria and Archaea
the deliberate use of viruses, bacteria, fungi, or toxins to cause harm or death to a population.
using biological agent introduced through the air, water supply or food in order to cause harm.
intentional threatening use of biological agents to cause death in large numbers for political reasons.
The first life appeared
about 3.5 billion years ago. Within the next billion years, two distinct groups of prokaryotes diverged: bacteria and archaea. An oxygen revolution began about 2.5 billion years ago when photosynthetic prokaryotes split water molecules, releasing oxygen gas into Earth's atmosphere. The oldest eukaryotic fossils are about 1.7 billion years old.
Eukaryotic cells evolved from
a prokaryotic community, a host cell containing even smaller prokaryotes.
are mostly microscopic and unicellular. Protists include protozoans and algae, including diatoms.
The first multicellular eukaryotes evolved
about a billion years ago as colonies of single-celled ancestors. Their modern descendants include- multicellular protists, such as seaweeds, animals, plants, and fungi.
The greatest diversification of animals was the so-called. All the major body plans (phyla) of animals had evolved by the end of that evolutionary eruption.
Until well into the nineteenth century, it was common knowledge that life could arise from nonliving matter
1862 famous experiments confirmed what many others had suspected: All life today, including microbes, arises only by the reproduction of preexisting life.
Although there is no evidence that spontaneous generation occurs today, conditions on the early Earth were very different. Earth's earliest atmosphere was void of oxygen to tear apart complex molecules. Energy sources such as lightning, volcanic activity, and ultraviolet sunlight were more intense than what we experience today. Most biologists now think that it is at least a credible hypothesis that chemical and physical processes in Earth's primordial environment could eventually have produced very simple cells through a sequence of stages. Debate abounds about the nature of those steps.
In 1953, built a contraption that simulated key conditions on early earth. His apparatus produced a variety of small organic molecules that are essential for life, including amino acids, the monomers and proteins. In the half-century since Miller's seminal experiments, many scientists have repeated and extended the research by varying such conditions as the composition of the ancient―atmosphere and ―sea
Miller's experiments have collectively produced
(a) all 20 amino acids, (b) several sugars, (c) lipids, (d) nucleotides that are monomers of DNA and RNA, and (e) ATP.
If the abiotic synthesis of life is correct
it should be possible to link organic monomers to form polymers (proteins, nucleic acids) without enzymes and other cellular equipment.
Graham-Cairnes & Smith
Researchers have observed such polymerization by dripping solutions of organic monomers onto hot sand, clay, or rock. The heat vaporizes the water in the solution and concentrates the monomers on the underlying substance. Some monomers then bind together.
conducted experiments that indicated that perhaps on early Earth, raindrops or waves may have splashed dilute solutions of organic monomers onto fresh lava or other hot rocks and then rinsed polypeptides and other polymers back into the sea.
What were the first genes like?
One hypothesis is that the first genes were short strands of RNA that replicated without the assistance of enzymes (proteins). In laboratory experiments, short RNA molecules can assemble spontaneously from nucleotide monomers without the presence of cells or enzymes. The result is a population of RNA molecules, each with some random sequences of monomers. Some molecules self-replicate, but they vary in their success at this reproduction. The results are a sort of molecular evolution in a test tube.
RNA genes are also likely because cells have catalytic RNA. These enzymes were discovered by scientist Cech and Altman and they were awarded the Nobel Prize in 1989. Early ribozymes may have catalyzed their own replication. The molecular biology of today may have been preceded by an "RNA world."
Formation of Pre-cells
The creation of membranes. The properties of life emerge from an interaction of molecules organized into higher levels of order. But such molecular teams would be much more efficient if they were packaged within membranes that kept the molecules close together in a solution that could be different from the surrounding environment. keep the molecules close together and in a solution different from the surrounding environment. Certain types of pre-cells store energy in the form of a voltage across their membranes, even discharging voltage much like nerve cells do. If specific enzymes are included, some pre-cells: show rudimentary metabolism, absorb substrates from their surroundings, and release products
For the first 75% of life's history, Earth was populated only by organisms that were microscopic and unicellular. Prokaryotes are both harmful and beneficial to humans. prokaryotes can be found everywhere on earth and outnumber all eukaryotes combined. More prokaryotes inhabit a handful of fertile soil or the mouth or skin of a single human than the total number of people who have ever lived. Prokaryotes also thrive in habitats too cold, too hot, too salty, too acidic, or too alkaline for any eukaryote.
Prokaryotes and disease
During the fourteenth century, bubonic plague killed about 25% of the European human population. Prokaryotes cause tuberculosis, cholera, many STDs and some types of food poisoning. Some prokaryotes are benign or even beneficial. Bacteria in our intestines provide us with important vitamins and mouths prevent harmful fungi from growing there. Prokaryotes also decompose dead organisms and recycle carbon and other vital chemical elements back and forth between organic matter and the soil and atmosphere. If prokaryotic decomposers were to disappear, the chemical cycles that sustain life would come to a halt.
The Structure, Function, and Reproduction of Prokaryotes
Nearly all prokaryotes have cell walls exterior to their plasma membranes. These walls are chemically different from the cellulose walls of plant cells. Some antibiotics, including the penicillins, kill certain bacteria by incapacitating an enzyme the microbes use to make their walls.
Spherical species are called (singular, coccus) from the Greek word for ―berries. Cocci that occur in clusters are called staphylococci (from the Greek staphyle, ―cluster of grapes), or staph for short (as in staph infections). Other cocci occur in chains called streptococci (from the Greek streptos, ―twisted) and include the bacteria that cause strep throat in humans.
A third group of prokaryotes is curved or spiral-shaped. The largest spiral-shaped prokaryotes are called spirochetes. The bacterium that causes syphilis, for example, is a spirochete. So is the culprit that causes Lyme disease.
Some species tend to aggregate transiently into groups of two or more cells. Others form true colonies, which are permanent aggregates of identical cells. Some exhibit a simple multicellular organization, with a division of labor between specialized types of cells. About half of all prokaryotic species are mobile using one or more flagella.
Unlike the arachae, most bacteria can not thrive in extreme environments. Instead, they survive by forming ―resting cells. Remain dormant for centuries and survive boiling water. Laboratories heat water to 121°C in special high-pressure autoclave machines. The food-canning industry uses similar methods to kill dangerous soil bacteria such as Clostridium botulinum, which produces the potentially fatal disease botulism.
can copy their DNA and divide nearly continuously. Bacteria show exponential growth. Their populations may double every 20 minutes. Fortunately, few bacterial populations can sustain exponential growth for long. Populations grow quickly but are soon limited by: nutrients, space, and accumulations of metabolic wastes. Refrigeration retards (but doesn't stop) bacterial growth.
refers to how an organism obtains two resources for synthesizing organic compounds- energy and a source of carbon
Autotrophs need only the inorganic compound CO2 as a carbon source. Heterotrophs require at least one organic nutrient (for example, glucose) as a source of carbon for making other organic compounds.
photosynthetic organisms that harness light energy to drive the synthesis of organic compounds from CO2. Examples include: cyanobacteria and all plants and algae.
extract energy from certain inorganic substances, such as hydrogen sulfide (H2S) or ammonia (NH3), and need only CO2 as a carbon source. This mode of nutrition is unique to certain prokaryotes. For example, prokaryotic species living around hot-water vents deep in the seas are the main food producers in those bizarre ecosystems.
can use light to generate ATP but must obtain their carbon in organic form. This mode of nutrition is restricted to certain prokaryotes.
must consume organic molecules for both energy and carbon. Examples are: many prokaryotes, certain protists, some plants, all fungi, and all animals.
Bacteria and Archaea. Prokaryotes lack a membrane-enclosed nucleus and other organelles found in eukaryotes. The traditional five-kingdom classification scheme emphasizes this fundamental difference in cellular organization. Both are prokaryotes, but they differ in many structural, biochemical, and physiological characteristics. There is also evidence that archaea are more closely related to eukaryotes than they are to bacteria. Most prokaryotes are bacteria.
The name (from the Greek archaio, ―ancient) refers to the antiquity of the group's origin from the earliest cells. (1) Today, most species of archaea inhabit extreme environments such as hot springs and salt ponds.
Some biologists refer to archaea as extremophiles, or ―lovers of the extreme. Extremophiles can survive harsh environments.
live in concentrated salt solutions such as Utah's Great Salt Lake and seawater-evaporating ponds used to produce salt.
Bacteria and other microorganisms that cause disease. Our body defenses check the growth of pathogens. Normal residents of the human body can make us sick when our defenses are weakened. Most pathogenic bacteria cause disease by producing one of two classes of poisons.
are not cell secretions but are chemical components of the cell walls of certain bacteria. All endotoxins induce the same general symptoms: fever, aches, and sometimes a dangerous drop in blood pressure (shock). Different species of Salmonella produce endotoxins that cause food poisoning and typhoid fever.
the first eukaryotes to evolve from prokaryote ancestors and are much more complex than prokaryotes.
The primal eukaryotes were the predecessors of
modern protists and all other eukaryotes—plants, fungi, and animals. protists are often defined by what they are not, they do not have the defining characteristics of plants, fungi, and animals
The endomembrane system
(all the membrane-enclosed organelles except mitochondria and chloroplasts) evolved from inward folds of the plasma membrane of a prokaryotic cell. Mitochondria and chloroplasts evolved by endosymbiosis, one species living within another. Chloroplasts and mitochondria evolved from small prokaryotes that established residence within other, larger prokaryotes. The ancestors of mitochondria may have been aerobic bacteria that were able to use oxygen to release large amounts of energy from organic molecules by cellular respiration. These first mitochondria may have been internal parasites or ingested by the host cell. In a similar way, photosynthetic bacteria ancestral to chloroplasts may have come to live inside a larger host cell. Because almost all eukaryotes have mitochondria but only some have chloroplasts, it is likely that mitochondria evolved first.
eventually became mutually beneficial. Increasing levels of oxygen would have favored cells with mitochondria. Heterotrophic hosts could derive nourishment from photosynthetic endosymbionts. The endosymbiosis theory was developed most extensively by Lynn Margulis of the University of Massachusetts.
Present-day mitochondria and chloroplasts
are similar to prokaryotic cells in a number of ways. Both types of organelles contain small amounts of DNA, RNA, and ribosomes, transcribe and translate their DNA into polypeptides that contribute to some of their own enzymes, and replicate their own DNA and reproduce within the cell by a process resembling the binary fission of prokaryotes.
live primarily by ingesting food and thrive in all types of aquatic environments, including wet soil and the watery environment inside animals. Most species eat bacteria or other protozoans, but some can absorb nutrients dissolved in the water. Protozoans that live as parasites in animals, though in the minority, cause some of the world's most harmful human diseases.
move by means of one or more flagella, are mostly free-living (nonparasitic), but some are parasites on humans.
is a flagellate that lives in the human intestine and can cause abdominal cramps and severe diarrhea.
show great flexibility, and lack of permanent locomotor organelles, and usually move by means of pseudopodia (singular, pseudopodium, false feet), temporary extensions of the cell. Amoebas can assume virtually any shape as they creep over diverse substrates.
are all parasitic (some causing serious human diseases) and are named for an apparatus at their apex that is specialized for penetrating host cells and tissues. This group includes Plasmodium, the parasite that causes malaria.
are protozoans that use locomotor structures called cilia to move and feed. Nearly all ciliates are free-living (nonparasitic). The best-known example is the freshwater ciliate Paramecium.
Slime molds resemble fungi in appearance and lifestyle, but the similarities are due to convergent evolution; slime molds and fungi are not at all closely related. The filamentous body of a slime mold, like that of a fungus, is an adaptation that increases exposure to the environment and facilitates their role as decomposers.
Plasmodial slime molds
named for the feeding stage in their life cycle, an amoeboid mass called a plasmodium (not to be confused with Plasmodium, the parasite that causes malaria), are actually a single cell with many nuclei, can reach several centimeters across, and can be found among leaf litter and other decaying material. Slime molds use their network of fine filaments to consume bacteria and bits of dead organic matter in the amoeboid style.
Cellular slime molds
have a life cycle that involves solitary cells and a sluglike colony. The feeding stage consists of solitary amoeboid cells using pseudopodia to feed on decaying organic matter. When food is depleted, the cells aggregate to form a sluglike colony that moves and functions as a single unit.
Photosynthetic protists are called algae (singular, alga). Their chloroplasts support food chains in freshwater and marine ecosystems. Many unicellular algae are components of plankton (from the Greek word planktos, ―wandering), the communities of organisms, mostly microscopic, that drift or swim weakly near the surfaces of ponds, lakes, and oceans. Specifically, planktonic algae are phytoplankton.
are abundant in the vast aquatic pastures of phytoplankton, have species-specific shapes reinforced by external plates made of cellulose, and have two beating flagella in perpendicular grooves that produce the spinning movement for which they are named. Population explosions sometimes cause warm coastal waters to turn pinkish-orange, a phenomenon known as a red tide. Toxins produced by some red-tide dinoflagellates have produced massive fish kills, especially in the tropics, and are deadly to humans as well.
Diatoms have glass cell walls containing silica. The cell wall consists of two halves that fit together like the bottom and lid of a shoebox. Diatoms store their food reserves in the form of an oil that provides buoyancy, keeping diatoms floating as phytoplankton near the sunlit surface. Massive accumulations of fossilized diatoms make up thick sediments known as diatomaceous earth, which is mined for its use as both a filtering material and an abrasive.
These algae are named for their grass-green chloroplasts. Unicellular green algae flourish in most freshwater lakes and ponds. Some species are flagellated. Of all photosynthetic protists, green algae are the most closely related to true plants.
are defined as large, multicellular marine algae, grow on rocky shores and just offshore beyond the zone of the pounding surf, have cell walls made of slimy and rubbery substances that cushion their bodies against the agitation of waves. Some seaweeds are as large and complex as many plants.
evolved many times among the ancestral stock of protists, (aggregate of (shown in specialization identical cells) cross section) leading to new waves of biological diversification
organisms that obtain nutrients by ingestion, eating food. Animals digest their food within their bodies after ingesting other organisms, dead or alive, whole or by the piece.
In most animals a gastrula develops after bastula. The gastrula has layers of cells that will form adult body parts and a primitive gut.
is a sexually immature form of the animal. Larvae are anatomically distinct from the adult form, usually eat different food, and may have different habitats.
A change of body form, called metamorphosis, eventually remodels the larva into the adult form. Most animals also have muscles and nerve cells to control the muscles.
exhibits a central axis in which all body parts radiate from sessile forms or plankton that can meet the environment equally well from all sides.
has equal right and left halves. move from place to place, have a distinct head end with a brain near a concentration of sense organs such as eyes, and are well adapted for movement, such as crawling, burrowing, or swimming.
Body cavities function
as fluid cushions, to separate growth and movement of internal organs from the outer body wall, and as hydrostatic skeletons (in soft-bodied animals such as earthworms). Body cavities may have first evolved as adaptations for burrowing.
completely lined by tissue derived from mesoderm. Among animals with a true coelom, there are two main groups that differ in details of embryonic development, including the mechanism of coelom formation. They are: the mollusks, annelids, and arthropods and the echinoderms and chordates.
Animals probably evolved from a colonial, flagellated protist that lived in Precambrian seas. By the late Precambrian, animals were already diverse. At the beginning of the Cambrian period, animal diversity exploded.
What caused the dramatic radiation of animal forms in the early Cambrian?
One hypothesis suggests that increasingly complex predator-prey relationships led to diverse adaptations for feeding, motility, and protection. Another hypothesis suggests that it was due to variation in how, when, and where genes that control the development of animal form are expressed.
To reconstruct the evolutionary history of animal phyla, researchers must depend mainly on clues from comparative anatomy and embryology. The first branch point distinguishes sponges from all other animals based on structural complexity.
move from place to place, have a distinct head end with a brain near a concentration of sense organs such as eyes, and are well adapted for movement, such as crawling, burrowing, or swimming.
consist of only one subphylum within the phylum Chordata, and are less than 5% of all animal species.
phylum Porifera are sessile (no movement); are the simplest animals, probably evolved very early from colonial protists, range in height from about 1 centimeter (cm) to 2 meters (m), have no nerves or muscles, and consist of about 9,000 species found in both marine and fresh water. The body of a sponge resembles a sac perforated with holes. Water is drawn through the pores into a central cavity, then flows out of the sponge through a larger opening, the osculum. Most sponges feed by collecting bacteria from the water that streams through their porous bodies.
flagelleated cells that trap bacteria in mucus and then engulf the food by phagocytosis.
pick up food from the choanocytes, digest it, and carry the nutrients to other cells. move using pseudopodia and manufacture the fibers that make up a sponge's skeleton. Sponge skeletons may be sharp and spurlike or softer and flexible.
phylum Cnidaria—ex. jellyfishes, sea anemones, coral animals, and hydras. radial symmetry, are carnivores, with cnidocytes (stinging cells) on their tentacles, have a body plan that is a sac with a central digestive compartment, the gastrovascular cavity, there is only one opening - incomplete digestive tract.
(for example, sea anemone) adheres to the substratum and extends its tentacles, waiting for prey.
The floating medusa
(for example, jellyfish), a flattened, mouth-down version of the polyp, moves freely in the water.
phylum Platyhelminthes—tapeworms, flukes, and planarians are the simplest bilateral animals, live in marine, freshwater, and damp terrestrial habitats, and include many parasitic species (flukes and tapeworms). Are hermaphroditic- have both sex organs. Flatworms are classified as free-living or parasistic (depend on a host) Planarians are examples of free-living (nonparasitic) flatworms.
Flatworms called blood flukes are parasitic affect about 250 million people in 70 countries and have complex life cycles that require more than one host species. For example the liver fluke has a snail and human host
parasitic- have a very long—up to 20 m long in humans—ribbonlike body with repeated parts; lack a digestive tract, living in and simply absorbing partially digested food in the intestines of their hosts; have a complex life cycle, usually involving more than one host; Individual segments of worms are called proglottids, parasitize many vertebrates, including humans. Humans can become infected with tapeworms by eating undercooked beef containing the worm's larvae. Large worms can cause intestinal blockage and rob nutrients. An orally administered drug called niclosamide kills the adult worms.
phylum Nematoda, Roundworms- get their common name from their cylindrical bodies, tapered at both ends, are among the most diverse and widespread of all animals, consist of about 90,000 known species (perhaps 10 times more actually exist), range in length from about 1 mm to 1 m, live in most aquatic habitats, in wet soil, and as parasites in the body fluids and tissues of plants and animals, and exhibit two evolutionary innovations not found in flatworms- a complete digestive tract, which is a digestive tube with two openings, and a body cavity (a pseudocoelom). Free-living roundworms in the soil are important decomposers. Some species are major agricultural pests that attack the roots of plants. Humans host at least 50 parasitic roundworm species including: pinworms, hookworms, and the parasite that causes trichinosis.
phylum Mollusca—snails, slugs, oysters, clams, octopuses, and squids. are soft-bodied animals; are usually protected by a hard shell (exceptions include slugs, squids, and octopuses have either reduced shells, most of which are internal or none at all); often feed by using a straplike rasping organ (radula) to scrape up food; consist of about 150,000 known species that are primarily marine although: some inhabit fresh water (snails, clams), and some live on land (snails, slugs). All mollusks have a similar body plan with three main parts: a muscular foot, usually used for movement; a visceral mass containing most of the internal organs; and a fold of tissue called the mantle that: drapes over the visceral mass and secretes the shell (if one is present).
include snails and slugs, are protected by single, spiraled shells into which the animals can retreat when threatened
include clams, oysters, mussels, and scallops, have shells divided into two halves that are hinged together, and are usually sedentary, living in sand or mud in marine and freshwater environments where they use their muscular foot for digging and anchoring. some species have the ability to change sex when necessary
include squids and octopuses; are built for speed and agility; are marine predators that use beaklike jaws and a radula (tongue -like structure) to crush or rip prey apart; have a mouth at the base of the foot, which is drawn out into several long tentacles for catching and holding prey; and rarely have a large shell (Nautilus), typically have a small and internal shell (squids), and sometimes have no shell at all (octopuses). these animals are deemed very intelligent
phylum Annelida—earthworms, polychaetes, and leeches are worms with body segmentation, the division of the body along its length into a series of repeated parts; consist of about 15,000 species; range in length from 1 mm to 3 m long; and live in the sea, most freshwater habitats, and damp soil.
eat their way through soil, extracting nutrients as the soil passes through the digestive tube, Undigested material, mixed with mucus secreted into the digestive tract, is eliminated as castings through the anus. Farmers value earthworms because: the animals till the earth and the castings improve the texture of the soil. Hermaphrodites, have few setae- hair like bristles
have segmental appendages, with many (poly) hard setae bristles that help the worm move; the appendages also increase the animal's surface area for gas exchange and elimination of metabolic wastes.
include blood-sucking forms, are mostly free-living carnivores, and typically live in fresh water. Leeches have been used in medicine. Until the twentieth century, blood-sucking leeches were frequently used by physicians for bloodletting. Leeches are currently used as a source of anticoagulant and to help relieve swelling in fingers or toes that have been sewn back on after accidents.
phylum Arthropoda—crustaceans, millipedes, centipedes, and insects are named for their jointed appendages, are represented in nearly all habitats of the biosphere. On the criteria of species diversity, distribution, and sheer numbers, arthropods must be regarded as the most successful of all animal phyla. Arthropods are segmented animals. Their appendages have become specialized for a great variety of functions: (1) walking, (2) feeding, (3) sensory reception, (4) copulation, and (5) defense. The body of an arthropod is completely covered by an exoskeleton (external skeleton) made of chitin.
can be thick where strength is needed and very thin where flexibility is required, protects the animal, provides points of attachment for muscles that move appendages, and must be shed and secreted again (the process of molting) to permit growth.
include scorpions, spiders, ticks, and mites; usually live on land; and usually have four pairs of walking legs and a specialized pair of feeding appendages.
(Crusty exoskeleton) include crabs, lobsters, crayfish, shrimps, and barnacles; are nearly all aquatic; and exhibit multiple pairs of specialized appendages. Pill bugs (roly-poly), commonly found under moist leaves and other organic debris, represent one group of crustaceans called isopods.
are terrestrial carnivores with poison claws and have one pair of long legs per body segment.
outnumber all other forms of life combined; live in almost every terrestrial habitat, freshwater, rarely in the seas, and in the air; typically have a three-part body: head, thorax, and abdomen; typically have three pairs of legs and one or two pairs of wings, all borne on the thorax; have heads with a pair of sensory antennae and a pair of eyes; and have mouthparts adapted for many functions—biting and chewing plant parts (for example, grasshoppers), lapping up fluids (for example, houseflies), and piercing surfaces and sucking blood (for example, mosquitoes). Flight is obviously one key to the great success of insects. The ability to fly helps to escape predators
Other insects undergo complete metamorphosis in which the larval stage looks entirely different from the adult stage. Larval stages are specialized for eating and growing. The adult stage is specialized for dispersal and reproduction. Metamorphosis from the larval to the adult occurs during a pupal stage- resting stage.
phylum Echinodermata—sea stars, sand dollars, and sea cucumbers. are named for their spiny surfaces; are all marine; most are sessile or slow moving; lack body segments; typically show bilateral symmetry as larva but radial symmetry as adults; first animals to exhibit endoskeleton (interior skeleton) constructed from hard plates just beneath the skin; have a water vascular system, a network of water-filled canals that circulates water throughout the echinoderm's body, facilitating gas exchange and waste disposal; and have tube feet connected to the water vascular system. Analysis of embryonic development reveals that echinoderms share an evolutionary branch with chordates. They share a common mechanism of coelom development and many other details of embryology.
Mammals, birds, reptiles, amphibians, and the various classes of fishes are all classified as vertebrates. The unique vertebrate features are: the cranium and backbone.
The phylum Chordata includes: the subphylum of Vertebrates and two subphyla of invertebrates, lancelets and tunicates. All chordates share four key features that appear in the embryo and sometimes in the adult. These are- a dorsal, hollow nerve cord (the chordate brain and spinal cord), a notochord, a flexible, longitudinal rod located between the digestive tract and the nerve cord, pharyngeal slits, and a post-anal tail.
lack jaws, are represented today by lampreys, are sometimes parasites that use their jawless mouths as suckers to attach to the sides of large fishes and draw blood.
The first jawed fishes
evolved about 400 million years ago, had jaws and two pairs of fins, included active predators, and included some fish that reached more than 10 m long. Today, most fish are carnivores.
(cartilaginous fishes—the sharks and rays) Cartilaginous fishes have a flexible skeleton made of cartilage; are usually adept predators; and are often fast swimmers with streamlined bodies, acute senses, and powerful jaws. Sharks do not have keen eyesight; have an acute sense of smell; have special electrosensors on the head that can detect minute electrical fields produced by muscle contractions in nearby animals; and have a lateral line system, a row of sensory organs running along each side of the body. Sensitive to changes in water pressure, the lateral line system enables a shark to detect minor vibrations caused by animals swimming in its neighborhood.
(the bony fishes). have a stiff skeleton reinforced by hard calcium salts; are common in the seas and in freshwater habitats; have a lateral line system, a keen sense of smell, and excellent eyesight; have a swim bladder, a gas-filled sac, that helps keep them buoyant/ afloat; and have a protective flap called an operculum that: covers a chamber housing the gills and moves to help a fish breathe without swimming. Sharks lack opercula and must swim to pass water over their gills. Most bony fishes, including trout, bass, perch, and tuna, are ray-finned fishes. Their fins are supported by thin, flexible skeletal rays.
are all extinct except for one species, a deep-sea dweller that may use its fins to waddle along the seafloor, and played a key role in the evolution of amphibians, the first terrestrial vertebrates.
class Amphibia (Dual Life) exhibit a mixture of aquatic and terrestrial adaptations, are abundant in damp habitats, depend on their moist skin to supplement gas exchange, depend on watery habitat for reproduction include frogs and salamanders, were the first vertebrates to colonize land and descended from fishes that had lungs and fins with muscles and skeletal supports strong enough to permit movement, however clumsy, on land.
Terrestrial vertebrates, including amphibians, reptiles, birds, and mammals are collectively called tetrapods. Tetrapod means four legs. Had our amphibian ancestors had three pairs of legs on their undersides instead of just two, we might be hexapods. This image seems silly, but serves to reinforce the point that evolution, as descent with modification, is constrained by history.
class Reptilia, Evolution of amniotic egg prevents dependency on water. Include about 6,500 species, mainly snakes, lizards, turtles, crocodiles, and alligators; have scales made of keratin that helps waterproof their skin while on land; use lungs and not skin to obtain most of their oxygen; first evolved amniotic eggs, a water-containing egg enclosed in a shell; and are ectotherms that regulate their internal temperature by behavior, requiring less than 10% of the calories required by a mammal of similar size.
class Aves, have amniotic eggs and scales on their legs, two reptilian traits; look quite different from modern reptiles because of their feathers and other distinctive flight equipment; include only a few flightless species, which evolved from flying ancestors; and include over 8,600 species. endotherms, using their own metabolic heat to maintain a steady body temperature.
Almost every element of bird anatomy is modified in some way that enhances flight. The bones have a honeycombed structure that makes them strong but light. For example, the huge seagoing frigate bird has a wingspan of more than 2 m, but its whole skeleton weighs only about 113 grams (about 4 ounces). The absence of some internal structures found in other vertebrates further lightens birds. Females have only one instead of two ovaries. Birds are toothless, using a gizzard to grind food. The powerful breast muscles, anchored to a keellike breastbone, provide power for flight (white meat on a turkey or chicken). Feathers are made of keratin. This is the same protein that forms our hair and fingernails, as well as the scales of reptiles. Feathers may have functioned first as insulation, helping birds retain body heat and only later being co-opted as flight gear.
is an ancient bird known from fossils in Bavarian limestone from Germany, is not considered the ancestor of modern birds (paleontologists place it on a side branch of the avian lineage), was probably derived from ancestral forms that also gave rise to modern birds, and has a skeletal anatomy that indicates it was a weak flyer, perhaps mainly a tree-dwelling glider.
class Mammalia, are mostly terrestrial, but include nearly 1,000 winged species (bats) and about 80 totally aquatic species (dolphins, porpoises, whales); and possess hair and mammary glands. Mammary glands produce milk to nourish young. Hair insulates the body and helps maintain a warm, constant internal temperature. Like birds, mammals are endotherms. The blue whale, nearly 30 m long, is the largest animal that has ever existed.There are three major groups of mammals: monotremes, marsupials and eutherians.
are egg-laying mammals. The duck-billed platypus is one of only three existing species. The female usually lays two eggs and incubates them in a leaf nest. After hatching, the young nurse by licking up milk secreted onto the mother's fur. Echidnas are also monotremes. Most mammals are born rather than hatched. During gestation in marsupials and eutherians, the embryos are nurtured inside the mother by the placenta.
the so-called pouched mammals: include kangaroos and koalas; live in Australia, New Zealand, and Central and South America; have diversified extensively over the past 60 million years, filling terrestrial habitats that on other continents are occupied by H mammals; and have a brief gestation period; and give birth to tiny, embryonic offspring that complete development while attached to the mother's nipples in an external pouch, the marsupium, on the mother's abdomen.
are also called placental mammals because their placentas provide the most intimate and long-lasting association between the mother and her developing young and make up almost 95% of the 4,500 species of living mammals, including: dogs, cats, cows, rodents, rabbits, bats, whales, and primates—monkeys, apes, and humans .
limber shoulder joints, which make it possible to brachiate (moving by swinging by the arms from one hold to another)
Enhanced Daytime Vision
eyes close together on the front of the face, providing better depth perception, an obvious advantage when brachiating
Better and Brains
brain expansion and elaboration produced a brain of bigger mass and complexity, especially for thought, language, and conscious movement.
care essential for young animals in the trees. Primates are among the most attentive parents of all mammals. Most primates have single births and nurture their offspring for a long time.
Bipedalism (walking upright) made possible through skeletal reorganization of the spinal column (backbone)
The oldest primate fossils are prosimians. Modern prosimians include the lemurs of Madagascar and the lorises, pottos, and tarsiers that live in tropical Africa and southern Asia.
in the New World (the Americas) are: arboreal and distinguished by a prehensile tail that functions as an extra appendage for brachiating. Although some Old World monkeys are also arboreal, their tails are not prehensile. Many Old World monkeys—including baboons, macaques, and mandrills—are mainly ground-dwellers.
Our closest anthropoid relatives
are the apes: gibbons, orangutans, gorillas, and chimpanzees. Chimpanzees are humans closest relatives with a genetic difference of less than 3%. Gorillas and chimpanzees are highly social. Apes have larger brains proportionate to body size than monkeys, and their behavior is consequently more adaptable.
the study of human evolution, focuses on this very thin slice of biological history.
Some Common Misconceptions of Humans and Apes
Our ancestors were not chimpanzees or any other modern apes. Chimpanzees and humans represent two divergent branches of the anthropoid tree that evolved from a common, less specialized ancestor. Chimps are not our parent species, but more like our phylogenetic siblings or cousins.
(Southern ape) Upright posture evolved well before our enlarged brain. Before Homo, several hominid species of the genus Australopithecus walked the African savanna. Fossil evidence now pushes bipedalism in A. afarensis back to at least 4 million years ago.
Homo habilis (handy man)
Enlargement of the human brain is first evident in fossils from East Africa dating to the latter part of the era of Australopithecus about 2.5 million years ago. Brain capacities were intermediate in size between those of the latest Australopithecus species and those of Homo sapiens. Simple handmade stone tools are sometimes found with the larger- brained fossils, which have been dubbed Homo habilis (―handy man).
The first species to extend humanity's range from its birthplace in Africa to other continents was Homo erectus, perhaps a descendant of H. habilis, about 1.8 million years ago. The spread may have been gradual and associated with a change in diet to a larger proportion of meat, requiring more geographic territory. Homo erectus was taller than H. habilis and had a larger brain capacity. Homo erectus resided in huts or caves, built fires, made clothes from animal skins, and designed stone tools that were more refined than the tools of Homo habilis.
Among these descendants of H. erectus were the Neanderthals who
lived in Europe, the Middle East, and parts of Asia from about 130,000 years ago to about 35,000 years ago. They are named Neanderthals because their fossils were first found in the Neander Valley of Germany. Compared to modern humans, Neanderthals: had slightly heavier browridges, less pronounced chins, and brains that, on average, were slightly larger than ours. had short and stocky bodies suited for cold weather
group these African fossils along with Neanderthals and various Asian and Australasian fossils as the earliest forms of our species, Homo sapiens. These regionally diverse descendants of H. erectus are sometimes referred to as archaic Homo sapiens.
modern humans evolved simultaneously in different parts of the world. The geographic diversity of humans originated between 1-2 million years ago. The great genetic similarity of all modern people is explained by interbreeding among neighboring populations throughout the range of humanity.
Out of Africa hypothesis (also called the replacement hypothesis) suggests that
(opposing the multiregional hypothesis) modern Homo sapiens arose from a single archaic group in Africa, the Neanderthals and other archaic peoples outside Africa were evolutionary dead ends, and modern humans spread out of Africa about 100,000 years ago and completely replaced the archaic H. sapiens in other regions. *Genetic evidence mostly supports the replacement hypothesis, particularly analyses of DNA found in the mitochondria of human cells (mtDNA). The mtDNA in today's global human population seems to be very uniform. Supporters of the replacement hypothesis argue that such uniformity could only stem from a single ancestral stock. Proponents of the multiregional model counter that interbreeding between populations can explain our great genetic similarity.
Cultural evolution has three major stages
Nomads hunted and gathered food on the African grasslands 2 million years ago. They made tools, organized communal activities, divided labor, and made beautiful ancient art. Agriculture, permanent settlements, and the first cities were developed in Africa, Eurasia, and the Americas about 10,000 to 15,000 years ago. The Industrial Revolution began in the eighteenth century. Since then, new technology has escalated exponentially.
is a change in an organism's DNA. A new mutation that is transmitted can immediately change the gene pool of a population by substituting one allele for another. Over the long term, mutation is very important to evolution because it is the original source of genetic variation that serves as the raw material for natural selection.
(a) leads to a balance between two or more contrasting morphs in a population and (b) might occur in a patchy environment, which favors different phenotypes in different patches.
is more important in the history of life, is more common than the nonbranching pattern, and only branching evolution can generate biological diversity by increasing the number of species.
live in anaerobic environments and release methane as a waste product. Methanogens live in: (a) swamps and produce swamp gas, (b) human intestines and produce intestinal gas, and (c) cattle digestive tracts and aid in cellulose digestion.
Sponges are multicellular but lack true tissues. The second branch point distinguishes animals that show radial symmetry (or are identical all around a central axis) from those that show bilateral symmetry (with only one way to split the animal into two equal halves). (1) Radial animals are
(a) sessile forms or plankton that (b) can meet the environment equally well from all sides.
Please allow access to your computer’s microphone to use Voice Recording.
Having trouble? Click here for help.
We can’t access your microphone!
Click the icon above to update your browser permissions and try again
Reload the page to try again!Reload
Press Cmd-0 to reset your zoom
Press Ctrl-0 to reset your zoom
It looks like your browser might be zoomed in or out. Your browser needs to be zoomed to a normal size to record audio.
Please upgrade Flash or install Chrome
to use Voice Recording.
For more help, see our troubleshooting page.
Your microphone is muted
For help fixing this issue, see this FAQ.
Star this term
You can study starred terms together