A species is a group of organisms that share similar characteristics and have the ability to reproduce offspring.
The special characteristics of a species is inherited when they are passed on from parent to offspring
The changes in these characteristics over time is called evolution.
Darwin’s Model of Evolution
The modern theory of evolution is based on the concept of natural selection . This was first proposed in a joint 1858 paper by Charles Darwin
Natural selection is the idea that individuals who possess advantageous genetic traits are more likely to survive and reproduce. In doing so, they increase the frequency of such traits in subsequent generations.
Natural selection “survival of the fittest"
This theory says that the organism that has traits to survive the best will survive and those that lack the best traits have a good chance of dying off.
This happens over a long period of time. Over this time the genetic makeup of a species could change its appearance so that it can survive better in an environment.
An example is the Galapagos finch has a bigger, stronger beak than normal finches, so it can eat the types of food in the Galapagos islands.
This change occurred inside of the DNA of the finch over a long period of time and through many generations.
So, one way that a new species can form is if a large population of organisms becomes separated into smaller populations that no longer breed with others of their own kind.
One way that a large group of animals can become separated is by a mountain range or a river.
So, lets say that we have a large population of lizards that became separated into two smaller populations by a river.
Now the lizards can only mate with other lizards that are in their environment.
Because the environment on each side of the river is going to be a little bit different, each small population is going develop different adaptations to their own environment.
These two new groups have now become a different species. And since all of the lizards in this example arose from one population we can then call them common ancestors.
Now each species has its own specific traits but all the species do share common traits that they inherited from their ancestors.
Speed of Evolution
Gradualism is the model that describes evolution as a slow, ongoing process by which one species changes into a new species.
It also states that a continuing series of mutations and variations of DNA will result in a new species.
This doesn’t explain the evolution of all species though. Some fossils show that some species changed to a new species very quickly.
Punctuated equilibrium shows that the mutations of a few genes results in the appearance of a new species over a short time span.
Punctuated equilibrium today
This still occurs today. Every time we expose a bacteria to a drug, the bacteria tries to make changes in its DNA so that the drug won’t kill it anymore.
The flu virus does this about every 30-50 years, and we are responsible to create new vaccines that are able to kill it.
Fossils Sec 6-2 H.W. pg 169 ques. 1-4
Most of the evidence for evolution comes from fossils. A fossil is the remains, imprint, or trace of a organism.
Scientists have the ability to study the past analyzing fossils, which are evidence of ancient life on Earth.
Fossils help scientists form pictures of the past and provide a history for life on Earth.
The Earths crust is a kind of graveyard that holds fossil remains of species that have lived throughout Earths history.
Most fossils are found within sedimentary rock, which is rock made of compressed sediments of sand, clay, mud and other rock.
Limestone is the sedimentary rock that we find most fossils.
These fossils are removed from the ground by scientists and are added to the fossil record.
The fossil record id the collection of all the fossils that scientists have recovered.
Determining a Fossils age
Scientists use relative dating to estimate a fossils age. Relative dating looks at the age of the rock the fossil is removed from.
Since rock is usually stacked up in layers we can estimate that if a fossil is in a rock layer, estimated to be 30 million years old, than the fossil is 30 million years old.
We also use radioactive elements to see how old a fossil is. Radioactive elements give off a certain amount of radiation and over time that amount lessens.
So if we test the amount of radiation emitted from a fossil we can tell the age.
The fossils record of Earth is a very vast one.
We have fossils from almost every major plant and animal group in our fossil record.
As vast as it is, the fossil record does not show a complete history.
Not every species is represented in the fossil record. And this is because it is much more common for an organism to decay before ever becoming a fossil.
Since not every organism is fossilized we also look at other things that suggest evolution.
One is embryology, or the study of how an organism develops from an embryo to an adult.
The embryos of a fish, a chicken, and a rabbit all look very similar and suggest an evolutionary relationship between vertebrate species. (pic on pg 167)
Similar structures of species also suggest a evolutionary relationship.
The arm bones in a frog, a human, a porpoise, and a bat are all very similar.
Also, vestigial structures, or structures that seem to have no function give us evidence of evolution.
An example is our appendix, we don’t use it but other large mammals use it to digest grass.
This suggests that our diet, long ago, greatly consisted of grass and plant material.
DNA and evolution
If we look a the DNA of a species we can see how closely related species really are.
Chimps, apes, orangutans all have 24 pairs of chromosomes and humans have 23 pairs.
We only differ from apes by about 3,000 genes. This suggests that our common ancestor were apes.
Primates Sec 6-3 H.W. pg 179 ques. 1-15
Humans, monkeys, and apes belong to a group of mammals called primates.
All primates have opposable thumbs, binocular vision, and flexible shoulders that allow rotation of the arm.
The opposable thumb is very important because it allows a primate to grasp and hold things.
Binocular vision allows depth perception or to be able to judge distances.
4-6 million years ago humanlike primates appeared and they are called Hominids.
They ate both meat and plants, and walked upright on two legs, and had larger brains than apes.
In 1974 Lucy was found. This was the first Hominid fossil ever discovered in Africa.
In the 1960’s a hominid named Homo habilis, or the handy man was found.
It is thought that this hominid gave rise to homo erectus, another human ancestor, because of the similar features they shared.
About 400,000 years ago Homo sapiens evolved.
Neanderthals were short, heavy bodied, thick boned humans that lived in families in caves and made stone tools to hunt animals.
Next, Cro-Magnon fossils were found in Asia, and are almost the same physically to modern humans.
There is evidence that they lived in caves, which they painted the walls of, and buried their dead.