Microevolution, on the other hand, refers to smaller evolutionary changes "within" species or populations. During microevolution changes in allele frequencies definitely do occur. Some biologists, Richard Dawkins in particular, have suggested that the gene is the object of selection. This was always challenged by Ernst Mayr "The individual is the entity which survives or not, which reproduces or not, and which reproduces successfully or not". Changes in gene frequency in populations is a by-product of what happens to individuals.
Paleontology, evolutionary developmental biology, and sequence analysis contribute much evidence for the patterns and processes that can be classified as macroevolution. An example of macroevolution is the appearance of feathers during the evolution of birds from one group of dinosaurs.
Within the modern evolutionary synthesis school of thought, macroevolution is thought of as the compounded effects of microevolution. Thus, the distinction between micro- and macroevolution is not a fundamental one – the only difference between them is of time and scale.
Some creationists have also adopted the term 'macroevolution' to describe the form of evolution they reject. They may accept that evolutionary change is possible within species (microevolution), but deny that one species can evolve into another (macroevolution). These arguments are rejected by biologists, who hold that there is ample evidence that macroevolution has occurred in the past.
Some examples of subjects whose study falls within the realm of macroevolution:
Russian entomologist Yuri Filipchenko (or Philipchenko, depending on the transliteration) first coined the terms 'macroevolution' and 'microevolution' in 1927 in his German language work, "Variabilität und Variatio".
Since then, their meanings have been revised several times and fallen into disfavour with many, who prefer to speak of biological evolution as one process.
Evolution as a whole is strongly supported by many kinds of evidence.
The issue for biologists is whether there is any sense in having the special term "macroevolution". The answer is yes for a few biologists who proposed one or more evolutionary mechanisms which worked above the species level. The ideas of punctuated equilibrium and species selection were suggested, but in each case most biologists felt they could be explained by the usual small-scale changes. This explains why 'macroevolution' is perhaps a term biologists do not need to use.
When discussing the topic, creationists use "strategically elastic" definitions of micro- and macroevolution. Macroevolution, by their definition, cannot be attained. Any observed evolutionary change is described by them as being "just microevolution".
The debate between biologists continues, with some biologists stating that there is significant evidence that other factors have acted during macroevolution, and others maintaining that macroevolution can still be fully explained by the mechanisms of microevolution.
Gene pool
A gene pool is the set of all possible variations (alleles) of all genes of a population. It is a concept in population genetics.
For example, plants have genes that say what colour their flowers will be. The gene pool of peas has an allele for red flowers and another one for white flowers.
Transcription (genetics)
Transcription is when RNA is made from DNA. The DNA sequence is copied by a special enzyme called RNA polymerase to make a matching RNA strand.
The matching RNA strand is a 'pre-messenger RNA'. Next, the non-coding introns are stripped out by a spliceosome. The remaining exons are put together to make a messenger RNA.
The product is called messenger RNA (mRNA) because it carries a genetic message from the DNA to the protein-making machinery of the cell. Transcription is the first step that leads to the expression of the genes.
The stretch of DNA that is transcribed into an RNA molecule is called a "transcription unit". This contains:
As in DNA replication, only one of the two DNA strands is transcribed. This strand is called the "template strand", because it provides the template for ordering the sequence of nucleotides in an RNA transcript. The other strand is called the "coding strand". Its sequence is the same as the newly created RNA transcript (except for thymine being substituted for uracil).
The DNA template strand is read 3' → 5' direction by RNA polymerase and the new RNA strand is synthesized in the 5'→ 3' direction. RNA polymerase binds to the 3' end of a gene (promoter) on the DNA template strand and travels toward the 5' end.
Roger D. Kornberg won the 2006 Nobel Prize in Chemistry "for his studies of the molecular basis of eukaryotic transcription".
William Hovell
William Hilton Hovell (April 26 1786 — November 9 1875) was an English explorer of Australia. Together with Hamilton Hume he explored much of Victoria.
William Hovell was born at Yarmouth, Norfolk, England. He joined the Royal Navy and became a captain. In October 1813, he moved to New South Wales with his wife Esther Arndell. He got work as a ship captain and made several trading trips along the coast and to New Zealand. In 1816 he was shipwrecked in Bass Strait. In 1819 he lived near Sydney and did some exploring to the south. He reached the Burragorang Valley in 1823.
In 1824, Governor Sir Thomas Brisbane asked Hovell to go with Hamilton Hume to explore the south part of New South Wales and Victoria. He wanted to know more about any rivers that might run south. Hovell was not an explorer but he knew how to navigate (find out where he was). There were problems deciding who was going to pay for the expedition. The two explorers bought most of the equipment. The government provided saddles, clothes, blankets and guns. Hume and Hovell left Sydney on October 3 1824, with six men, five bullocks, three horses and two carts. The Murrumbidgee River was in flood so they had to make one of the carts into a kind of boat to get across. The men, horses, and bullocks swam over. A day or two later, in rough hilly country, they had great difficulty in finding a path for the carts. On October 27 they decided to leave them behind. They came to a large river on November 16, which Hovell called "Hume's River" "he being the first that saw it". This was the Murray River renamed by Charles Sturt a few years later. It was impossible to cross here (near the site of Albury), but after a few days they found a better place. They built the rough frame of a boat and managed to get across. By December 3, they had reached the Goulburn River. During the next ten days it was hard traveling through rough country, but they did get to more level and open land.
On December 16, they saw Port Phillip Bay. They went along its shores in south-westerly direction. They came to what is now Corio Bay near Geelong. Hovell made a mistake of one degree in working out the longitude. The explorers thought that they were on Western Port Bay. The party went back on December 18, and went more to the west. This was an easier journey. By January 8 1825, they came to the end of their food. For a few days they lived on fish and a kangaroo they were able to shoot. On January 16 they reached the carts they had left behind them, and 2 days later came to Lake George.