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Evolution is the process that results in heritable changes in a population, which is spread over many generations. Evolutionary theory states that groups of organisms change with the passage of time, mainly as a result of natural selection, so that descendants differ morphologically and physiologically from their ancestors. Many of these changes are said to arise spontaneously because of mutations.
Such inherited changes may render the altered species in a more favourable position within its environment (for eg: longer legs for running) or it may be less favourable (a change in colouration making the individual more conspicuous within its usual habitat).
Therefore - evolution is a change in the gene pool of a population over time.
Lamarck was a pioneer in this evolutionary field - therefore he is sometimes
referred to as 'the father of evolution'.
Lamarck was a french natural philosopher who united a wide range of scientific
interests under general principles. He is considered the most influential evolutionary
thinker prior to Charles Darwin (see below)
Lamarck theorised that the mechanism of evolutionary change was environmental
and inherited, he proposed that evolution resulted from the inheritance of
acquired characteristics.
This theory put forward the notion that organs or physical traits which assist an organism in survival are strengthened; whilst other traits that do not benefit the organism progressively atrophy and though disuse. These traits would then be passed onto the organisms offspring.
An example of a Lamarck-like statement based on his theory of 'acquired characteristics'
using the giraffe would go as such:
However there are some major flaws in Lamarck's theory, as it does not hold well with reality. As a crude example:
Can you think of any other examples that might hold true using the 'inheritance of acquired characteristics' theory that Lamarck proposed?
His studies and publications gave rise to an interest in the field of evolution, and influenced later scientists and scientific theories. In particularly Lamarck greatly influenced Darwin's theories on evolution.
Darwin was a British naturalist who became famous for his theories of evolution and natural selection. The concepts of which still hold true today.
Like several scientists before him, Darwin believed all the life on earth evolved
(developed gradually) over millions of years from a few common ancestors. His
famous work - entitled 'The Origin of Species by means
of Natural Selection' (published in 1859) was amazingly forward thinking
for the time.
Darwin's evolutionary selection theory states that variation within species occurs randomly and that the survival or extinction of each organism is determined by that organism's ability to adapt to its environment.
Natural Selection is the process in nature by which, according to Darwin's theory of evolution, only the organisms best adapted to their environment tend to survive and transmit their genetic characters in increasing numbers to succeeding generations while those less adapted tend to be eliminated.
Can you think of any examples that illustrate the 'natural selection' theory that Darwin proposed?
He set these theories forth in his book aforementioned book (The Origin of Species)
Darwin's work had a tremendous impact on religious thought. Many people strongly opposed the idea of evolution because it conflicted with their religious convictions.
This branch of modern evolutionary theory has been termed 'NeoDarwinism' as it is largely based on Darwin's original findings. However it has modified to include the findings of modern genetics (i.e: knowledge which Darwin lacked during his era)
Such vital information was able to explain how genetic variations can occur in species populations, and how these traits are passed onto offspring and later generations.
Johann Gregor Mendel (1822 -1884)
It was not until the early 1850's that an Austrian monk - Johann Gregor Mendel unknowingly started research that would later provide the missing pieces for Lamarck and Darwin's evolutionary jigsaw puzzle.
Mendel was an experimental biologist, and after study at University he entered the monastery in 1843. This provided the perfect opportunity to continue his academic work and botantical studies.
Mendel is often termed the Father of Genetics, as his studies were the first ever conducted into the science of genetics. Through years of experiments with plants, chiefly garden peas, he discovered the principle of the inheritance of characteristics through the combination of genes from parent cells - which are still being taught today.
Only in 1900 was Mendel's astonishing work recognized and his remarkable findings made renowned.
It has long been accepted that all land animals with backbones - including humans - are descended from one small group of fish that left the water about 365 million years ago.
Gradually over many years, the legs and tails of Eustenopteron grew longer and stronger and evolved into the earliest amphibians - these were the first large land animals.
The first amphibians never strayed far from the water in which they hatched. Many lived in or near the shallow waters of the great coal swamps which covered large parts of the Earth's prehistoric surface. These water dwelling amphibians often stayed fishlike in appearance, and the young amphibians had gills, just as tadpoles of today.
The short legs and long, fish-like body of Eryops show that it would rarely have come out onto land, yet it was one of a large group of amphibians whose descendants included the reptiles, the first true land animals, which lived 280 million years ago
The reptiles were the first backboned creatures to spend all their time out
of the water.
How were they able to adjust to life on land?
The chief secret of the first reptiles was their egg. An amphibian's egg is
small and soft, like frogspawn, and will soon dry out and die if left out of
water. The much larger reptile egg is protected from drying out by its tough,
waterproof shell. Safe inside its shell, the young reptile is nourished by a
large supply of yolk until it is ready to hatch out.
As the reptiles increased and flourished, they came to dominate the Earth. The amphibians on the other hand, retreated and dwindled until they became the rather small and easily overlooked group of today.
The Mesozoic Era (often termed the
Age of Reptiles) was a very long stretch of time - around 200 million years.
With almost the whole ecosystem at their disposal, the dinosaurs flourished
during the Mesozoic Era.
During this time nearly every large animal that walked on the land, swam in
the water or glided in the air was a reptile.
The very first large reptiles gave way to a varied host of later types, including those most impressive reptiles - the dinosaurs.
A vast array of dinosaur species and types roamed the earth during the Mesozoic Era - which were so diverse in appearance, behaviour and habitat.
There are at present 500 known dinosaur species (however this number is based
on just a few fragments of bone or a single tooth. In the end, there are about
200 definite classifications)
And that's only the ones we know about!
The family tree diagram shows dinosaurs and their close relatives.
In the center is a small dinosaur ancestor, the reptile Euparkeria which lived
in the Triassic age of the Mesozoic Era.
This group of reptile gave rise to the various groups of dinosaurs. Euparkeria
and its relatives were also the ancestors of many other later reptiles (namely
the crocodiles, pterosaurs and birds).
Of the animals shown on the tree - only the crocodiles and birds exist today.
Paleontologists have estimated that dinosaurs died out about 65 million years ago, at the end of the Cretaceous Period of the Mesozoic Era, as no dinosaurs fossils have been found in rocks past that era.
No one has discovered why dinosaurs became extinct so suddenly but there are a great many theories (see worksheet 3)
The world that came after the dinosaurs was more like our own. It was dominated
by mammals and birds, animals that are
most familiar today.
Mammals increased in size and variety and soon became the dominant land animals.
Plants too, became more like those of today. Not all the dinosaur's close relatives
died out. The crocodile is a living cousin of the dinosaurs. But in number and
variety - the most successful descendants of the dinosaurs are the birds.
The Mesozoic is divided into three time periods. Although dinosaurs dominated the scene, birds and mammals also appeared during the Mesozoic, as well as deciduous trees and flowering plants. Vertebrates diversified throughout the Triassic, developing into various creatures such as large marine reptiles, mammals, and the primitive forebears of lizards, turtles, and crocodiles. Birds evolved from reptilian ancestors during the Late Jurassic, and two important modern mammal groups--the placentals and the marsupials--made their appearance in the Late Cretaceous. Plant life also exhibited a gradual change toward more modern forms during the course of the Mesozoic. Whereas seed-fern flora had predominated in the Triassic, forests of palmlike gymnosperms known as cycads and conifers proliferated under the tropical and temperate conditions that prevailed during the Jurassic. The first flowering plants, or angiosperms, appeared by the Cretaceous. They radiated rapidly, supplanting many of the primitive plant groups to become the dominant flora form by the end of the Mesozoic. The Mesozoic closed with a mass extinction that annihilated many forms of life. Although the dinosaurs and many flying and marine reptiles were killed off, many smaller species of animals also perished. The Late Cretaceous extinctions have been variously attributed to such phenomena as global tectonics, draining of the epicontinental seas, northward migration of the continents into different climatic zones with much cooler conditions, intensified volcanic activity, and a catastrophic meteorite impact. The extinctions spanned millions of years, a fact that has led some researchers to believe that, after an era of dominance among various forms of life, decay of the Mesozoic ecosystem had set in. In fact, the Cretaceous extinction event may very well have had multiple causes.
Dinosaurs Index | Lesson Idea 1 - Art Primary | Lesson Idea 2 - Art | Lesson Idea 3 - English | Lesson Idea 4 - Science | Worksheet 1 | Worksheet 2 | Resource 1 | Resource 2 | Resource 3 | Activitysheet 1 | Associated Web Links