Changes through time
Charles Darwin Contribution
Charles Darwin was a naturalist who sailed on the HMS Beagle in 1831. As a naturalist he would observe
and takes notes on the flora and fauna of the areas the ship visited. Darwin was amazed by the amount of
diversity or different species he saw. A species is a group of organisms that look similar and can produce
fertile offspring.
Darwin visited the Galapagos islands located on the west coast of South America in 1835. On the
Galapagos, Darwin observed a wide variety of organisms such as the swimming iguanas, giant tortoises and
finches. He noticed that the organisms on the island were different than those organisms he saw on the
mainland. For example the iguanas on the island had claws while those on the mainland did not. The beaks
of the island finches were also different from the beaks of the mainland finches. Darwin inferred that those
organisms on the island had come from the mainland. Darwin noticed the differences in the traits between
organisms allowed them fill in a specific role or niche in the ecosystem. Since the finches had different beak
shapes they ate different types of food and did not compete for the same resource. Those with larger thicker
beaks had an adaptation that allowed them to eat larger seeds while those with thinner beaks ate mainly
insects. (Adaptations: An adaptation is any trait that enables an organism to survive in their environment.)
Darwin's theory of evolution:
(Remember a theory is: The best explanation for a natural phenomenon that is backed by lots of data and
research.)
After many years of review Darwin believed that the finches that came from the mainland of South America
to the Galapagos were faced with different environmental conditions. Those finches that had genetic
variations that enabled them to survive in the new habitat did survive and reproduced. Their offspring then
had the same adaptations as the parent and were able to survive. Those organisms that did not have the
adaptation did not survive or reproduce. Over time the population contained members with the adaptation
and those who did not have it did not survive. From these observations Darwin developed his theory of
evolution that states that a species will gradually change over time (many generations), and become better
suited or adapted to their environment. Darwin added that evolution occurs as a result of natural selection.
Natural selection is the process in which organisms that are better suited to their environment will most
likely survive and produce offspring than other members of the same species. Those who are not suited to the
environment die off.
For example: Peppered Moths in Pre-industrial England.
When a species does not have the traits it needs to survive in its environment, or to survive a change in its
environment, extinction may occur. Extinction occurs when all the members of a species disappear from the
Earth. So where do variations that Darwin saw come from? In some cases, genetic variations are caused by
a change in the genetic code, or DNA itself. This type of change is called a mutation. A mutation can be
passed on to offspring if the mutation takes place in the sex or reproductive cells of its parents. This type of
mutation results in offspring inheriting different traits or characteristics than their parents. Mutations can
result in unfavorable or favorable changes or adaptations in the genetic code of offspring. Unfavorable
changes in offspring can reduce an organism’s ability to exist or survive in its environment. Favorable
changes improve an organism’s ability to survive in its environment.
Sometimes favorable mutations produce inherited structures,
functions, or behaviors that enable a species to survive and reproduce. These inherited traits are called
adaptations.
Structural adaptations include such things as body color, body covering, different types of body parts such as
beaks and claws, mimicry, vision, and camouflage.
Functional adaptations include biological processes that allow an organism to respond to its environment.
Examples:
1. cactus storing water in their stems,
2. chameleon changing colors
3. Producing venom
4. Secreting poison
5. Skin turning brown after exposure to sun
6. Photosynthesis
Behavioral adaptations are certain activities or actions that living things do in response to their environment
in order to meet their needs for food, water, shelter, and protection.
Examples: beavers slapping their tails and squirrels chattering to warn when a predator is near, bird
migration, squirrels burrowing nuts, bears hibernating.
In summary organisms and their environments change over time. The process by which living organisms
change over time is called the theory of evolution. The theory of evolution proposes that species change
through the processes of mutation, adaptation, natural selection, and extinction.
Evidence that supports the Theory of Evolution.
1. Fossils
2. Anatomical evidence-homologous structures
3. DNA
4. Geographic distribution
5. Embryological development
Fossil Evidence for Evolution
These processes of species change have occurred over long periods of time on the Earth, which scientists
believe may be close to 4.6 billion years old. We have learned about the age of the Earth and its changing
inhabitants by studying rocks and the remains of plants and animals preserved in rocks. These remains are
called fossils.
Fossils are usually found in sedimentary rocks. Sedimentary rocks are formed when small pieces of rock,
called sediments, are dropped by water, wind, or ice and build up in layers. These layers eventually harden
and turn into rock. In addition to pieces of rock, sometimes sediments contain organic materials such as dead
plants and
animals. Many fossils form when organic materials are quickly buried by clay, sand, and other sediments.
Fossil remains can include animal skeletons, shells, insects trapped in amber, seeds, leaf imprints, dung, and
DNA. Fossils provide scientists with a record of organisms, species changes, and events in Earth’s history.
Radiometric dating uses radioactive atoms to estimate how long ago rocks and the fossils in them were
formed. Radioactive atoms are atoms that release many types of energy due to their unstable nuclei. Over
long periods of time these radioactive atoms lose some of their energy and change or decay into more stable
atoms. Radiometric dating measures the ratio of unstable atoms to stable atoms to help determine the age of
the rock and any fossils found in sedimentary rock nearby.
Anatomical Evidence
Anatomical evidence is also used to support the theory of evolution. Scientists study the similarities in body
structure among different species such as whales and humans. Such similarities as skeletal structure provide
evidence that two very different organisms may
have evolved from a common ancestor.
Homologous Structures are a structure that has a different function in different organisms but share a
common ancestry. In vertebrates the limb bones develop in similar patterns.
DNA evidence
Scientists also use evidence from genetic information to support the theory of evolution. They compare the
DNA of different species and can tell how closely they are related by the number of similarities they find.
Scientists believe that organisms with similar genes are descended from a common ancestor. For example
scientists believe that bears and raccoons come from a common ancestor that lived over 40 million years ago.
Distribution of Organisms as Evidence for Evolution
The distribution of organisms on Earth is also used as evidence for the theory of evolution. Scientists have
found that there is an unequal distribution of organisms on Earth. A species that is found in a particular
ecosystem, such as cacti in the deserts of North America, is not found in a similar ecosystem such as the
deserts of Africa. Scientists believe that each species originated or began in one location and from this point
of origin spread out until it was stopped by a physical geographic barrier such an ocean, an
environmental barrier such as a colder climate, or an ecological barrier such as competition from another
species. Other geographic distributions also help to explain evolution. For instance, alligators are located
only in certain regions of the world, presumably because they have evolved in those regions. The islands of
Australia and New Zealand have populations of animals found nowhere else in the world because of their
isolated environments. (marsupials and monotremes)
Embryological Development as Evidence for Evolution
Developmental evidence is also used. Scientists study developing embryos and look for similarities in early
development. Similarities such as throat slits and tails in developing embryos suggest that organisms being
studied are related. For example scientists have found strikingly similarities in the embryos of many
vertebrates such as turtles, fish, chickens, pigs, and humans. Embryonic structures of different species show
significant similarities.
Embryo is the early stages of vertebrate development.
In review, Darwin developed the Theory of Evolution which stated that all organisms change over time due
to natural selection, adaptations, mutations and extinction.
Evidence for evolution can be found in the fossil record, homologous structures, DNA, distribution of
organisms and embryological development.