Does life evolve (change over time)?  Can a species give rise over time to new species?  For that matter, what is a species?

• Concept of species is pre-dates the birth of the Greek philosopher, Aristotle.
• Basic unit of classifying different organisms, whether you use scientific or common names.  The Latin word specere, from which our word "species" is derived, means "to look at."  The word originally referred to the outward appearance of an organism.
• Examples of different species that the average person recognizes include cardinals, bluebirds, snow geese, cats, dogs, petunias, roses, and so on.
• Greek species concept.  Aristotle (384-322 B.C.) and Theophrastus (late fourth and early third centuries B.C.) conceived of species as unstable and highly changeable.  Aristotle believed in spontaneous generation of species, and regarded all kinds of crosses between species as feasible, likely, and a means for the creative construction of new species.  For example:  Rampant hybridization could produce a new species. A camel could hybridize with a panther to produce a giraffe. An Arabian camel crossed with a wild boar produced the two-humped Bactrian camel.  Oppian argued that a camel crossed with a sparrow produced an ostrich.
• Some Greek philosophers, including Aristotle and Plato, believed in idealism.  For every thing in the universe (e.g., shapes), there existed the ideal or perfect form.  All other objects were variations of the ideal form and drew their properties from such entities.  Consequently, when idealism was applied to the human concept of species (particularly by theologians and naturalists towards the end of the Middle Ages), these became seen as merely variations of ideal forms.  These forms were arranged in continuum of complexity from simple to more complex.
• In the 1750's, the naturalist Buffon contributed to the idea that species were discrete entities. Theologians and naturalists of the time argued for the fixity of species, the view that each species remained as created by God, according to the accounts given in the Book of Genesis in the Judeo-Christian Bible.
• By the middle of the 18th century, the discreteness and stability of species were generally recognized, setting the scene for Linnaeus and other taxonomists to collect representative members of each species, preserve these in collections as the representative or type specimen of that species, provide it with a Latin binomial (two word, i.e., genus and specific epithet) species name, and describe its physical appearance in Latin. Thus, developed the typological species concept in which all members of a species were of one basic type.  This type did not vary significantly from place to place or through time.
• Classification by taxonomists were also arranged into a hierarchy - refer to Table 15.3 on page 374 in the textbook.
• Kingdom =>Division (Phylum)=>Class=>Order=>Family=>Genus=>Specific epithet

  *The genus and the specific eptithet when combined represents the two word (binomial) name of the species - e.g., like Quercus alba (the white oak tree) .

  *Sometimes the name(s) or the intitial(s) of the person(s) responsible for describing the species appear after the name - e.g., Quercus alba L. (L. stands for Linnaeus).

   

• Another prevailing idea of the time - Great Chain of Being - species were fixed into place by God (each species being created separately).  Taxonomists during the 18th through the first part of the 19th century worked to pigeon-hole all species, because it was thought that this would give them insight into the Mind of the Creator.
• During the 18th and 19th century, species were thought to be immutable, unchanging, and fixed.   Species don't mix, and when they do hybridize, the progeny are usually sterile - HYBRID STERILITY (fertile donkey and fertile horse = sterile mule). Mules are sterile because female horses (mares) are 2N = 64 (egg = 32 chromosomes) and the male donkey is 2N = 62 (sperm = 31) which combine during fertilization to produce a mule zygote with a chromosome number of 2N = 61. Consequently when the gonads of a mule attempts to produce gametes (a process made possible through meiosis – chromosomes don't necessarily have a partner or homologue to pair with during Prophase I and separate from during Metaphase I). The result are gametes with varying numbers of chromosomes, hence these are incompetent and are likely not to form a viable zygote when combined with their counterpart (i.e., an egg with a sperm).
• Mind set of people prior and early into the 19th century - species do not evolve, they are static or constant.  A dog is always a dog, a cat is always a cat ...........

  Biogeography - study of the world distribution of plants, animals, and other organisms.

Europeans started to explore the world in the 16th century and brought many exotic and unusual plants and animals back with them.  They discovered that Biodiversity is high! According to E. O. Wilson, there are currently over 1,413,000 species of plants, animals, bacteria, protozoa, fungi, etc. that have been described.

• 751,000 species of insects
• 281,000 species of all other animals
• 248,400 species of higher plants (ferns, flowering plants, gymnosperms)
• 69,000 species of fungi
• 26,900 species of algae
• 30,800 species of protozoa
• 4,800 bacteria and related forms
• 1,000 types of viruses (alive?)

Naturalists also discovered that the distribution of species varied from place to place.  Many places contained unique or endemic species!  Example:  The mammals in Australia are marsupials (e.g., kangaroos, Tasmanian wolf, bandicoots, Koala bears, etc.), whereas mammals found in most other regions of the world are placental mammals (e.g., sloths, primates, wolves, cats, bears, rabbits, rats, etc.).

• Why are some species only found in certain parts of the world?
• Why are different kinds of organism similar in some respects, but obviously different?
• Examples:  Tasmanian wolf vs. gray wolf; American cacti vs. African euphorbs - refer to Figure 14.10 on page 337 in the textbook.  Each type has an ecological counterpart in a different region of the world.

Comparative Anatomy

• Homologous structures - same structures are modified for different functions.

1.  Example:  Bones in vertebrate forelimbs (humerus, radius, ulna, carpals, metacarpal, phalanges) are found in limbs of seals (flippers), wing (bat and bird), human arm, animal leg (carnivore paw).

2.  Example:  Leaves of plants are found in most land plants but they do not always function as modules of photosynthesis.  In venus-fly trap and pitcher plants, the leaves are modified to trap insects - refer to Figure 2.18 on page 41 in the textbook, in cactus plants the leaves are reduced to spines for protection and decrease transpiration rates - refer to Figures 2.3 and 2.25 on pages 31 and 46 in the textbook., in sweet pea the leaves are long and spindly (tendrils) and used for support, in onions the leaves are used to store food and form a bulb, and in the maternity plant the leaves produce plantlets for vegetative reproduction.

Vestigial structures - structures that are present but serve no discernible purpose.

1.  Examples:  pelvic bones in boa constrictors, wings and feathers in flightless birds (e.g., ostriches, emus); blind eyes in cave-dwelling species.  In the Indian pipe plant, rudimentary leaves are produced but the plant is unable to photosynthesize (no chlorophyll) - refer to Figure 2.22 on page 42 in the textbook..

• Embryology- presence of a structures that suggest a relatedness to other life forms.

  1.  Example:  human embryos have pharyngeal arches, a two-chambered heart, and a tail which disappears before birth!  Pharyngeal arches in fish develop into the gills and the jaw.  In humans, pharyngeal arches do not develop into gills, but into the lower jaw, hyoid bone, and larynx.

  2.  Karl Ernst Von Baer in 1828 noted that the earlier stages of embryos of more advanced species resembled the earlier stages of development in more primitive species.  Ernst Heinrich Haeckel in 1867 formulated the "biogenetic law", that is, ontogeny recapitulates phylogeny, or in other words, embryological development retraces ancestry.

  3.  Although in a strict sense, an embryo does not retrace it's ancestry as it develops, the physical evidence does suggest that developmental pathways appear to be constrained along certain avenues of development.  This probably goes hand-in-hand with the conservative nature of the genes which govern this process and the need to insure that embryological development concludes itself in the production of a viable offspring (whether the embryo is from an animal or a plant).

Fossil Record

• Fossils are often found layered in sedimentary rock.  Complex fossils are found in newer strata, while simpler forms are found in older layers.   Conditions are not always conducive to fossil formation.  Usually only harder components of an organism are fossilized.  Erosion destroys many fossils and sedimentary layers through the action of wind and rain.  Consequently, the fossil record is not complete but derived from data collected from different parts of the world.  Dating sedimentary layers suggests that these are ancient - refer to Figure 14.3 on page 331 in the textbook.
• Darwin found fossils in the Andes mountains suggesting that the land had once be the bed of an ocean.  Geologic forces raised the sea floor up to produce land and mountains.
• Species have gone extinct.  Some people suggested that fossilized creatures had not gone extinct, but that they would be discovered once the Americas was complete.  Generally, this is not so, (dinosaurs, trilobites, and tree ferns are dead), although many extant organisms are found in the fossil record.  On the other hand, ginkgo trees (refer to the photograph on page 326 or Figure 17.25 on page 434 in the textbook) and coelacanths (a fish) are referred to as living fossils, precisely because these were described from fossilized remains before being rediscovered as extant species.
• Refer to 17.2 Perspective on page 433 in the textbook.

Artificial Selection

• Domesticated Plants and Animals have been selected and bred by humans for various characteristics.  Breeds includes, dogs, cats, horses, pigeons, fruits, vegetable.....
• Forage kale or wild cabbage (Brassica oleracea) is the ancestor of kohlrabi (expanded just above the roots), cauliflower (abortive flowers, that are kept white by tying the leaves at the base around the inflorescence so chlorophyll won't form), broccoli (fertile flower buds), cabbage (terminal bud), brussels sprouts (axillary buds), and kale (leaves).  All these varieties belong to the same biological species despite their physical differences.  You can cross broccoli with cabbage and get fertile offspring  - refer to 2.1 Perspective on page 45 in the textbook.

TAKE HOME MESSAGE:  species appear to be malleable, and given a long enough period of time and the proper conditions, might give rise to a new species!  If so, evolution occurs.  Evolution is an inferred fact.

 Evolution as a theory:

	Charles Darwin (1859)  - refer to Figure 14.1 on page 329 in the textbook - "On the origin of species by means of natural selection, or the preservation of favored races in the struggle for life" and Alfred Wallace (1858).
	The Theory of evolution through Natural Selection and Modification with descent.
	Charles Darwin (1809-1882) - English naturalist
	From 1831-1835 - naturalist on the H. M. S. Beagle, explored South America, the Galápagos Islands - refer to Figure 14.2 on page 330 in the textbook.
	The facts of animal distributionA and the relations between living/fossil animalsB learned in his travels led him to consider the origins of species.  The "species problem".

• ^ASimilar kinds of organisms confined to different geographic regions often showed pronounced differences in some of their traits.
• ^BNow extinct glyptodonts resembled extant or living armadillos.  If these animals were created at the same time, why were glyptodonts extinct, while armadillos still alive.  Could armadillos have arisen from glyptodonts?

14 species of Darwin's finches - constitute a separate subfamily found nowhere else in the world.  13 species are thought to have evolved on the Galápagos Islands, and one on Cocos Island (NE of the Galápagos Islands) - refer to Figure 14.4 on page 332 in the textbook..

• In 1838, Darwin read the essay by Thomas Malthus, "Essay on Population".  Populations increase at geometric ratio^a until checked by limiting factors (e.g., food, shelter, fuel).  He came to the recognition of the struggle for existence within all population and concluded favorable variations would be preserved while unfavorable variations would not - refer to Figure 14.6 on page 333 in the textbook.
• In 1844, Darwin wrote a summary of theory but continued to gather data.

^aReproductive potential of most species higher than actually possible.  For example:

1.  Paramecium (0.25 mm long) can divided about 600 times per year.  If all survived and continued to divide, their bulk would exceed that of the earth after several months.

2.  Darwin assumed that elephants breed at 30 years to 100 years, each female producing but 6 young, in 750 years about 19,000,000 would be alive.

3.  Puffball mushrooms - Giant puffball (7 trillion spores), spores become fruit bodies they would griddle the earth more than 5 times; or fruit bodies would stretch twice to the sun and back, and form a mass eight hundred times the weight of the globe.

• Alfred Russel Wallace (1823-1913) studying the rich fauna and flora of the Malay Archipelago, independently and rapidly arrived at similar conclusions.  In 1858, he shared his insights to Darwin.  Wallace's essay and a brief of Darwin's conclusions were published together in the same year.
• Darwin's and Wallace's theory of descent with modification through variation and natural selection:  Basic Assumptions or tenets of how Darwin and Wallace conceived evolution to occur were as follows: (Items highlighted in red and italics in the following text came to light during the second half of the 19th century and during the first part of the 20th century).

1.  Many more individuals are born in each generation than will survive and reproduce.
2.  There is variation among individuals; they are not identical in all their characteristics.

SOURCE OF VARIATION IS MUTATION: A RANDOM PROCESS:   => Mutation - any novel genetic change in the gene complement or genotype relative to the parental genotypes, beyond that achieved by genetic recombination during meiosis.

3.  Individuals with certain characteristics have a better chance of surviving and reproducing than individuals with other characteristics.

NATURAL SELECTION: A NONRANDOM PROCESS IMPOSED BY THE ENVIRONMENT.

Darwin assumed that traits were heritable without knowing whether it was true or not or understanding the mechanism by which this could take place.

Darwin was a proponent of pangenesis to explain the mechanism of inheritance, which was a good guess but incorrect. Gregor Mendel 1865 - founder of genetics (science dealing with heredity) discovered the basic laws that govern heredity, known as the Particulate (factor or gene) theory of inheritance.  Unfortunately Mendel's work was not appreciated until it was rediscovered 35 years later.  It wasn't until the 20th century that the "weakest assumption or link" of Darwin's theory was eliminated through the integration of genetics into his theory - A.K.A. NeoDarwinism or the Modern Synthesis.

5.  Vast spans of time have been available for change.

Darwin was influenced by Lyell's Principles of Geology and Uniformitarionism - enormous time spans involved in geological changes - natural forces persisted over time - current processes of geological activity were sufficient to explain past geological phenomena.

Lyell and Darwin were opposed to the concept of catastrophism == i.e., different strata of fossil were the result of devastating extinctions followed by "new creation" and progressionism with each new creation event leading to newer more advanced forms.

6.  Natural Selection: current thoughts and examples - refer to Figure 14.15 to 14.17 on pages 340-343 in the textbook.
  The   following links are web pages you may want to visit - FYI!

"There is grandeur in this view of life, with its several powers, having been originally breathed by the Creator into a few forms or into one; and that, whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved."   -Charles Darwin, Origin of Species - 1859.

What is a species?  A definition of species is not necessarily a straight forward thing.  Even Darwin recognized that it might be difficult to pen a definition for species concept that would apply to all species.  He tended to regard species as "varieties", being a bit ambiguous so as not be locked into particular definition.  In this century a number of species concepts have been proposed but none are universally agreed upon.  Ernst Mayr is a proponent of the "Biological Species Concept (also called the Isolation Species Concept).  A species according to Mayr consists of groups of actually or potentially interbreeding natural populations that produce viable offspring.  Species integrity is maintained by mechanism that promote reproductive isolation - refer to Tables 15.1 and 15.2 on page 360 in your textbook.  This species concept applies primarily to sexually-reproducing organisms including most animals and many plants.  Opposition to this species concept comes from those biologists who believe it does not adequately describe groups of organisms that are asexually-reproducing or for those species that appear to be discrete entities but can hybridize easily with other species producing fertile offspring.  Many plants fall at the too extremes of the reproductive spectrum with what A. R. Templeton refers to as the problem of too little or too much sexual reproduction.