An informal poll: Which is the most highly evolved species?
EVOLUTION is defined as change over time.
ORGANIC EVOLUTION is the genetic (and phenotypic) change of living
organisms over time.
We are the products of our ancestors' choices.
Another poll, this one with three parts.
Now the big question...why?
Common Misconceptions About Evolution
MISCONCEPTION: Evolution is "only a theory".
FACT: Organic evolution is not a theory at all.
Evolution is a process by which living organisms change from one generation to the next.
The only thing theoretical about evolution is how it happens.
MISCONCEPTION: Evolution describes the origin of life on earth.
FACT: Evolution is not the process by which life originated. It is the process by which life has changed since its origin. The origin of life and the evolution of life are two separate concepts.
MISCONCEPTION: Evolutionary theory implies that life evolved, and is evolving, by chance.
FACT: While random processes (genetic drift) do contribute to evolution, natural selection is a non-random process that can result in evolution happening in a particular "direction" (i.e., creating populations of organisms that are adapted to a particular environment).
MISCONCEPTION: Evolution is progress: evolving organisms are getting better.
FACT: Evolution is a process, and it has no value system. Populations change, but how does one define "better"? Organisms evolve to fit their environments, which means diversity of form and function. But there is no one form or function that is superior to all others.
MISCONCEPTION: Individual organisms evolve during their lifetimes.
FACT: Individuals adapt as they live and age. Only populations of organisms evolve, from one generation to the next.
MISCONCEPTION: Evolution occurs only gradually, over very long periods of time.
FACT: Relatively small genetic changes can sometimes result in major phenotypic changes. If these are passed to the next generation, they can magnify (especially if they are adaptive), and major evolutionary modifications can occur relatively rapidly.
MISCONCEPTION: Species are distinct natural entities that can be clearly defined and recognized.
FACT: The biological definition of a species is "a group of similar organisms that can interbreed in nature to produce fertile, viable offspring." But there not always a clear line between species. Hybridization between groups humans have defined as "species" can sometimes produce fertile, viable offspring. There is more than one definition of a species, and living organisms don't necessarily pay attention to those definitions.
MISCONCEPTION: Genetic drift occurs only in small populations.
FACT: Even very large populations undergo random genetic change from one generation to the next. Some alleles will be passed on, and others may disappear. The global population of humans alive today is genetically different from the global population of humans that lived 10,000 years ago, and part of that is due to simple genetic drift.
MISCONCEPTION: Our species is no longer evolving.
FACT: Genetic drift and natural selection are alive and well in Homo sapiens populations. Pathogens, parasites, and other environmental factors all can affect individuals, and sometimes they can cause differential reproduction among individuals of different genotype.
MISCONCEPTION: Because evolution is slow, humans cannot influence it.
FACT: Humans are influencing evolution as we speak. For example, our activities that produce pollution and climate change are driving evolution of species that can reproduce quickly enough to evolve in response. Others may simply go extinct, if they cannot cope with the relatively rapid changes wrought by humans.
Evolution and Biodiversity
The Convention on Biological Diversity defines biodiversity as
"the variability among living organisms from all sources including, inter alia (i.e., "among other things"), terrestrial, marine and other aquatic ecosystems and the ecological complexes of which they are a part; this includes diversity within species, between species, and of ecosystems."
Biodiversity is the variety of living species on
Depending on the source, anywhere from 1.2 to 1.7 million species of eukaryotes have been
cataloged and described in a scientific paper (i.e., been physically described and given a scientific name in a refereed, scientific journal journal).
A biologist who names and classifies living things is known as a
A biologist who studies the evolutionary relationships between living
organisms is a systematist. (Most systematists are also taxonomists.)
species (biological definition): a population or series of populations within
which free gene flow occurs under natural conditions. (i.e., a group of similar organisms that can interbreed in nature to produce fertile, viable offspring.)
conspecifics are members of the same species. For example, all the Homo sapiens in this classroom are conspecifics.
type material - a collection of specimens of a single species (or subspecies) that was cited in the original, published description of that new species (or subspecies).
holotype: The individual member of a species (in the type collection) on whose physical description the description of the entire species is based.
paratypes: the unlucky conspecifics in the type collection, other than the holotype.
(Below, the holotype of the snail, Zospeum tholussum, is outlined in solid white, and the paratypes in dotted lines.)
How Much Genetic Variety Are We Talking About?
Recall that the genome is the full DNA sequence of an organism.
A diploid organism has two copies of its genome in each of its diploid cells, one from each parent. The two copies are not necessarily identical.
In eukaryotes, we must distinguish the
nuclear genome - the genome in a eukaryotic nucleus (usually 2 non-identical copies)
organelle genome - the genome in a mitochondrion or chloroplast (may be multiple, identical copies)
The number of genes in a genome depends on the species. Numbers range from about 1000 (in a typical bacterium)
to more than 400,000 (in some ferns and flowering plants).
Mammalian genomes are still being quantified, and differ across species. The human genome is believed to contain fewer than 20,000 protein-coding genes.
How much information is that? Let's consider a hypothetical eukaryote with 100,000 nuclear genes.
If you were to stretch out the DNA strands in 100,000 eukaryotic genes and lay them end to end, the strand would be about 1m long. (20 Angstroms in diameter)
Magnify this strand to the diameter of a
common wrapping string (about 0.5mm), and the length suddenly stretches to 960 km (almost 600 miles).
At this magnification, there would be about 50 nucleotides per centimeter
The full information therein, if translated into 10 pt.
font and printed, would fill all 15 (printed) editions of the Encyclopedia Brittanica published
Here's just the Eleventh Edition, to give you an idea of how many books that is.
And that's the genetic information in just one single individual with 100,000 genes.
Multiply that number of volumes by all the individual members of a species, and then by potentially
30 million species of eukaryotes alone, and you get an idea of the staggering genetic library that has evolved over the 4 billion years that life
has inhabited earth.
Biodiversity is Disappearing
Most species that have existed on earth are now extinct.
But the rate of extinction currently going on qualifies as a mass extinction similar to large-scale loss of species that have occurred only a few times in the earth's past.
Currently, the main causes of loss of species can be traced back to one very successful species, Homo sapiens, that has caused and is now causing Loss of Biodiversity (H.I.P.P.O.):
complex ecosystems (diverse) protect their component species
unknown future benefits
Let's consider one problem, loss of genetic diversity.
inbreeding is defined as a mating between closely related individuals.
(i.e., In an inbreeding population, individuals choose relatives--rather than non-relatives--as mates more often than would be predicted by the frequencies of relatives and non-relatives in the population if mating were random.)
outbreeding is defined as a mating between unrelated conspecifics.
(i.e., In an outbreeding population, individuals choose non-relatives--rather than relatives--as mates more often than would be predicted by the frequencies of relatives and non-relatives in the population if mating were random.)
We're all aware that in most human societies, there are taboos against inbreeding
Because relatives are more likely to share genes in general, they are also more likely to share deleterious (harmful) alleles of certain genes, as well.
Mating between close relatives increases the likelihood that such alleles will be inherited in homozygous condition by their offspring.
If the alleles are recessive (which is often the case with deleterious alleles, since dominant ones usually don't last long in a natural population), the harmful condition is more likely to be expressed.
Many well-known genetic disorders in humans are due to the inheritance of two recessive alleles, and is often due to some degree of mating between relatives (even if they are distant relatives from the same ethnic group).
The smaller the size of a wild population, the more genetically uniform it
will be, and the more likely there will be inbreeding. As a species becomes rare, it is more likely to undergo inbreeding and express harmful genetic conditions.
This is also demonstrated by human artificial selection to produce "desirable" characteristics in domestic animals and plants by inbreeding them. Unfortunately, less desirable alleles of other genes may also come along for the ride, and their expression is more likely in highly inbred cultivars (plants) and breeds (animals).
This phenomenon is nicely illustrated by purebred dogs.
A Paucity of Domesticity
Although there are millions of species on earth, humans have managed to domesticate (or semi-domesticate) relatively few of them.
The combination of few domestic species produced and refined by inbreeding can set the stage for economic disaster.
The Saga ofZea mays: domestic corn
In the mid 1970's highly inbred Zea mays crops in the U.S. were attacked by an extremely
virulent viral blight that threatened to completely wipe out these economically vital crops.
With little genetic diversity, crops were dying to the blight. They had no genetic resistance to it.
A team of biologists working in Western Mexico to catalog species discovered a one hectare
stand of a previously unrecognized wild cousin of Zea mays:
(on the right, a wild cousin of maize, on the left, maize, and in between, their F1 hybrid).
It was located in an area that was being logged out to be replaced by cattle pasture.
Zea mays (2n=20)
A close relative, Zea perennis (2n = 40) - can't hybridize
This new relative, Z. diploperennis (2n = 20)
The new species was hybridized with domestic corn.
Breeding the two had two potential benefits:
Zea mays is an annual. It flowers once, bears fruit and dies. Being a perennial, Z. diploperennis could pass on genes to Z. mays x Z. diploperennis hybrids that might confer perennial growth. This would reduce soil erosion and the cost of corn production.
Z. diploperennis was resistant or immune to seven different types of viral corn blight, one of which was threatening to wipe out U.S. corn crops.
Viral resistance is among the dominant alleles passed on by the wild corn.
Losing wild species means losing the genetic "safety net" they provide.
Wilderness as a resource
There are several different ways that
humans may view the value of wild species.
anthropocentric view: non-human species are important
only in so far as they can benefit humans (e.g., provide products such as food, medicines or other commodities)
biocentric view: non-human species are important to save
for their own, intrinsic value.
Unfortuantely, many biocentric people tend to have a subjective view
of which species are valuable, often focusing their preservation efforts on
large, charismatic species (whales, Spotted Owls, penguins, baby seals, deer with big, brown
eyes) and ignoring the value of less humanlike species.
ecocentric view: biodiversity and ecosystems should be
preserved--not just individual species or populations--because it is the
whole, working system that maintains diversity.
Disassembling ecosystems would be like disassembling a human body: the
component parts don't function individually the way the whole does.
Ecologically significant species
indicator species - a plant or animal species that, by its presence, abundance, lack of abundance, or chemical composition, demonstrates some distinctive aspect of the character or quality of an environment.
example: Northern Spotted Owl
This animal was at the center of a huge bioethics controversy in the mid 1980s, pitting environmentalists and scientists against the logging community.
keystone species - a species upon which many other species in an
ecosystem rely for their survival
examples: plankton in the world's oceans Coyote in fragmented Southern California
native species - one that occurs in the area where it evolved.
endemic species - a species native to a particular area that is found nowhere else on earth.
exotic species - one that has been introduced artificially to an area where it did not evolve.
invasive exotic species - an exotic species that aggressively displaces native species (often with dire consequences for native ecosystems).
Invasive Exotic Plants in Southern Florida: The Big, Evil Three
terebinthifolius) --all very
invasive, pernicious "weed" species that out-compete native species and can
eventually lead to native species extinction.
They also may be
allelopathic--producing toxic compounds that deter growth of competing plants nearby. (This can be valuable to humans seeking
bioactive compounds--but don't assume that a product labeled "natural" is
safe. Those plants mean business.)
For more information on exotic invasive plant species in southern Florida,
threatened species - still relatively abundant in isolated areas of
its former range, but likely to become more scarce, usually due to habitat
loss. (example: American Bald Eagle)
endangered species - so few individuals left that
extinction is imminent. (examples: California Condor, Snow Leopard, Siberian
Tiger, Snail Darter, cheetah, white rhino etc.)
Note that one should use great caution when defining threatened and
The threatened Florida Panther is not a distinct species, but rather is a small subspecies of the Mountain Lion Felis concolor (Felis concolor coreyi) that may not have existed until human intrusion into mountain lion habitat cut the population off from the rest of the species' range.
Over the course of the next 14 weeks, we will be studying species in the context of evolution. This is a term that's been in the news a lot lately. So before we even embark on our journey, let's have a little Word about Science....
Biology is a Natural Science
The difference between a Miracle and a Fact is exactly the difference
between a mermaid and a seal.
-- Mark Twain
The Natural Sciences (Physics, Chemistry, Biology, Geology, etc.) are
governed by the necessity of their adherents to utilize
The Scientific Method
...to add to the knowledge of their field.
As you should know by now, the scientific method is a precise set of rules followed by
researchers/investigators in the natural sciences.
If you're not sure you recall, then Review the Scientific Method here. (You'll be responsible for knowing this on an exam, and in your future life as a professional science person.)