Download Biology Chapter 15 notes 15-1 Evolution Concepts Theory of

Biology Chapter 15 notes
15-1
Evolution Concepts
Theory of evolution states that species change over time.
Fossils provide one form of evidence for evolution. Other evidence includes: similarities
in morphology and development; DNA, RNA and protein sequences.
Fossils
Fossil – trace of a long-dead organism.
Sedimentary fossils are formed when sediment covers the decaying organism. Over
time hard minerals replace the organisms remains, leaving a fossil
Mold – fossil that is an imprint of the shape of an organism.
Cast – a mold that has filled in with hard minerals.
Robert Hooke in 1668 published his conclusion that fossils are remains of plants and
animals.
Nicolaus Steno in 1669 proposed the law of superposition – states that successive
layers of rock or soil were deposited on top of one another by wind or water.
The lower stratum is the oldest, top stratum the most recent. Fossils in a single stratum
are from the same age.
Under Steno’s law, someone could establish a relative age of a fossil. (one fossil is
relatively older than a fossil above it)
The fossil’s absolute age could be established from the amount of sediment deposited
above the fossil.
Succession of Forms
According to the fossil record, some organisms lived a while, then disappeared – extinct
Fossil records also indicate mass extinctions – brief periods where a large number of
species disappear.
Mass extinctions probably resulted from drastic changes in the environment, possibly
from volcanic activity that filled the atmosphere with ash and blocked out the sun for
long periods of time.
Biogeography
- the study of the geographical distribution of fossils and of living organisms.
Comparison of recently formed fossil types with types of organisms in the same area
shows that new organisms arise in areas where similar forms already lived.
Armadillos appeared in North and South America, where glyptodonts lived in the past.
Burgess Shale
800 m above sea level in the Canadian Rockies lies the Burgess Shale.
Contains a very diverse fossil bed from the Cambrian period 550 million years ago. It is
considered an explosion of life from the Precambrian Era, which only had simple
eukaryotic and prokaryotic cells. Many of these animals are not similar at all to modern
day animals.
15-2
Biological evolution is the change of populations of organisms over many generations.
Population –group of organisms of one species that interbreed.
Early scientists observed that new life-forms appeared to be modifications of fossil
forms found in the same geological area. This suggests a natural modification process
is at work.
- a glyptodont is a fossil
form of an armadillo.
Lamarck’s Ideas
French scientist Jean Baptiste de Lamarck proposed that species undergo modifications
over time. His belief was that similar species descended from a common ancestor –
living species came from fossil forms.
To explain how species change, he hypothesized that acquired traits were passed to
offspring. Acquired traits are not determined by genes.
Acquired traits arise from a result of the organism’s experience or behavior.
An example he used: Over time the webbed-feet of water birds resulted from repeated
stretching of the membrane between the toes. So the trait was preserved.
Although this idea was disproved, it lead the way for the evolution theory.
IMPORTANT – individual organisms do NOT evolve, populations evolve over time.
Modern Evolutionary Thought
Mid 1800s –Charles Darwin and Alfred Wallace independently proposed the idea that
species were modified by natural selection.
Natural Selection – when organisms that are best suited for their environment
reproduce more successfully than other organisms.
Natural Selection
Example of natural selection – bacterial resistance to antibiotics. Overtime strains of
bacteria become resistant to antibiotics, because they have the right gene that makes
the bacteria resistant to the antibiotics. As those bacteria with the gene reproduce,
eventually the entire population is resistant.
A No-no of Natural Selection
Question: Why do leopards have spots?
No-no: “Leopards evolved their spots IN ORDER TO survive better in their
environment.”
More Accurate: “Spots are a beneficial trait that have arisen from generations of
populations of leopards.”
IMPORTANT – Evolution is not active!
Charles Darwin
In 1831 was hired as a naturalist on the ship H.M.S. Beagle for a five-year expedition to
collect specimens from South America and the South Pacific.
In 1859 he published his ideas of evolutionary theory in his book “The Origin of
Species.”
15-3
Darwin’s Voyage
Uniformitarianism – principle that geological structures of the Earth resulted from cycles
of observable processes and that these same processes operate continuously through
time. So rivers form the same way they did millions of years ago.
While on his voyage Darwin incorporated the idea of uniformitarianism into his works on
natural selection. (If geological processes take a long time, maybe changes in
environments take a long time too.)
Darwin discovered fossil shells of marine organisms in rock beds above 14,000 feet in
elevation in mountains.
Darwin reasoned that the formation of mountain ranges would slowly change habitats,
requiring organisms that lived there to adapt to these changes.
Darwin’s Finches
Darwin found 13 similar species of finches on the Galapagos Islands. Each bird had a
bill specially designed for its food. But similarities implied the birds came from a
common ancestor.
Because the Galapagos Islands are young islands (about 5 million years old), Darwin
assumed that the offspring of the original finches have been adapting to different
environments for a relatively short time.
Darwin reasoned that over millions of years, many large differences could accumulate
between species.
The Origin of Species
In 1858 Alfred Wallace sent Darwin his studies on evolution. This prompted Darwin to
finish his studies on natural selection and present both his and Wallace’s works side by
side to the Linnaean Society. The following year in 1859 Darwin finished his works On
the Origin of Species by Means of Natural Selection.
Darwin’s Theories
Two ideas of evolution Darwin presented:
Descent with modification
Natural selection
Descent with Modification
The newer forms appearing in the fossil record are actually the modified descendents of
older species. Similar to Lamarck’s idea, but he included that all species had descended
from one or a few original types of life.
Modification by Natural Selection
- Explains how evolution occurs
Thomas Malthus published a paper on human populations that observed that the growth
of the human population was limited by factors like war, disease or supply of natural
resources. Darwin figured that the environment limits the growth of populations by
increasing the rate of death and/or decreasing the rate of reproduction.
Organisms with a greater number of favorable traits tend to leave a larger number of
offspring than organisms with fewer beneficial traits.
Darwin called that different degrees of reproduction among organisms in a population
natural selection.
A population of organisms adapts to their environment as their proportion of genes for
favorable traits increases.
In an evolving population, a single organism’s genetic contribution to the next
generation is termed fitness.
An individual with high fitness is well adapted to its environment and reproduces more
successfully than an individual with low fitness.
A favorable trait is said to give the organism an adaptive advantage. A favorable trait
that does not enhance reproductive success does not contribute to evolution.
15.3 Evolution in Process
Evolution Thoughts
The environment dictates only the direction and extent of evolution (shows where
organisms came from and how much organisms have changed).
Natural selection changes species over time.
Since natural resources are limited, all organisms must compete for resources.
Evidence of Evolution
Beaks are modifications of a feature found in an ancestor common to all birds. Similar
features that originated in a shared ancestor are called homologous structures.
Limbs can look different and vary in function (wing and an arm), but are derived from
the same structures in the embryo.
Presence of homologous structures in different species indicate a recent ancestor.
Analogous structures serve identical functions, look somewhat alike, but have a
different embryological development.
Example: the hummingbird and the humming moth. Both hover to suck nectar from
flowers, but do not share anatomical or embryological similarity between their wings
(Their wings are not the same.)
Vestigial Structures
Features that serve no function that were useful to the ancestor.
Example: human tailbones and whale pelvic bones.
The human tailbone is homologous structure to functional tails of other vertebrates.
Species that have evolved from a common ancestor should have certain characteristics
in common.
Embryological Similarities
Early stages of different vertebrate embryos are extremely similar to each other. These
similarities fade as the embryo develops. This is another indication that vertebrates
share a common ancestry.
Molecular Similarities
Darwin was unaware of genetic similarities like RNA, DNA or homologous proteins.
Amino acid sequences in human blood and gorilla blood differ by one amino acid. Frog
blood amino acid sequences and humans differ by 67 amino acids.
The number of differences in amino acids in homologous proteins of two species is
proportional to the length of time that has passed since the two species shared a
common ancestor.
Coevolution – the change of two or more species in close association with each other.
Species can coevolve, like parasites and their hosts or plants and the animals that
pollinate them.
Convergent Evolution
organisms that look similar, but ancestral types are different. It occurs because the
environment selects similar phenotypes.
Example – sharks and dolphins.
Divergent Evolution
Two or more related populations or species become more and more dissimilar, often
resulting in a new species. This is usually due to differing habitats – open niches.
Adaptive Radiation
A type of divergent evolution where many related species evolve from a single ancestral
species.
Example: Galapagos finches
Artificial Selection
Process of speeding up divergence artificially by selective breeding.
Example: Domestic dogs