B3 Life On Earth

A. The Variety of Life

1) Why are living things all different?

2) What is a species?

3) What is some evidence for evolution

Species

A species is a group of organisms so similar that:

They can breed together

Their offspring can also breed (they are fertile )

Horses and Donkeys are separate species …although they CAN breed together…

Their offspring, a MULE, is INFERTILE

Similarly, a lion + a tiger makes an infertile LIGER

Whereas these dogs are all the same species

Darwin developed his theory in part because of his study of how dogs and pigeons were bred. He knew several breeders of dogs and asked them how they selected certain traits. According to the American Kennel Club, there are over 150 different dog breeds, from tiny Chihuahuas to giant Great Danes, but they are the same species ( Canis familiaris ) and all are descendants of wolves.

Same species, different breed

A breed is a group of domestic animals within a species whose appearance has been determined by artificial selection over many generations.

An individual of one breed will be able to successfully reproduce with an individual of another breed, but both breeds’ distinctive characteristics can be lost, this makes a mixed breed animal.

Breeders taught Darwin how they selected certain characteristics and how they ensured that those characteristics made it into the next generation. That’s how different dog breeds are made.

If a breeder wanted a dog with a curly coat, he or she would allow curly-coated dogs to breed and not allow them to breed with straight-coated dogs.

In nature, the most well-adapted animals are more likely to survive and reproduce, but in dog breeding, the dogs with the desirable characteristics are allowed to reproduce by the breeders.

There is genetic variation in animals These are White-cheeked rosellas, which are common throughout parts of Australia.

Genetic variation is an essential element of evolving organisms.

Mutation (base substitution) is the ultimate source of this variation, and generates new alleles at particular loci (parts of chromosome).

At a higher level, chromosomal changes generate variants across multiple genes and involve large pieces of DNA.

Environmental Variation

Environmental variation can be caused by factors like climate, diet, physical accidents, culture and lifestyle.

Many kinds of variation are influenced by both environmental and genetic factors, because although our genes decide what characteristics we inherit, our environment affects how these inherited characteristics develop.

Identical twins are a good example of the interaction between inheritance and environment, as they are genetically the same. All the differences you see between identical twins, therefore - in personality, tastes, and aptitude for example - are due to differences in their experience or environment.

Basic evolutionary change is a two-step process.

The first step is the production of genetic variation in every generation.

In sexually reproducing organisms, genetic variation is created by random mutations in the DNA of eggs and sperm cells and also by genetic recombination.

New genes may also be introduced into a population when an individual of the same species migrates over from another population.

The second step of evolutionary change is the choosing of the genotypes that will produce the next generation. This is where natural selection operates, while chance plays a less important role.

These mating soldier beetles ( Chauliognathus pennsylvanicus , family Cantharidae) are in the process of generating variation.

Soon the chromosomes in their eggs and sperm cells will recombine and generate the genes of their offspring.

Any mutations in the parent beetles' DNAs will also be passed on to their offspring.

All the while, the beetles are under the ever watchful eyes of natural selection , which means that the individuals that are good at getting food, avoiding predators and other dangers or finding a mate are more likely to survive and leave offspring than those that are not as good.

Evidence for Evolution - Fossils Throughout the fossil record, we can see evidence for the transitions from simple to more complex living organisms. Almost all fossils found are extinct species e.g Burgess Shale from Cambrian

Burgess Shale – 520 mya

Archaeopteryx's many features of dinosaurs such as the jaws with teeth, tiny forelimbs with three claws, a long tail and a head covered with scales while body, wings and tail were covered with feathers as in a bird provides strong evidence of the dinosaur ancestry of birds, and, more generally, of the validity of the Theory of Evolution.

Chimps, Humans 96 Percent the Same, Gene Study Finds Stefan Lovgren for National Geographic News August 31, 2005 Scientists have sequenced the genome of the chimpanzee and found that humans are 96 percent similar to the great ape species. "Darwin wasn't just provocative in saying that we descend from the apes—he didn't go far enough," said Frans de Waal, a primate scientist at Emory University in Atlanta, Georgia. "We are apes in every way, from our long arms and tailless bodies to our habits and temperament."

But then there is always a little disagreement – some people believe that we are more closely related to the orangutan, who then might be an ancestor to early man…

There are variations in pathogens – disease causing microbes too! The top section represents a population of bacteria before exposure to an antibiotic. The middle section shows the population directly after exposure, the phase in which selection took place. The last section shows the distribution of resistance in a new generation of bacteria.

Darwin’s finches are a classic example of evolution in action. They comprise 14 closely related species that differ in beak shapes and sizes and live on the Galapagos islands.

The group includes ground-dwelling birds ( Geospiza ) that feed on different sized seeds or cactus flowers and tree-dwelling birds ( Camarynchus ) that feed on different sized insects or types of fruit, and each beak is adapted for a specialized feeding task.

Cataloguing the birds he collected in 1835 helped Darwin formulate his theory of evolution because he realized that all the finch species arose from one ancestral form that had adapted to a variety of feeding conditions. Today the finches are considered a perfect example of adaptive radiation , in which one species diversifies into many to exploit a wide range of habitats.

Earlier attempts: Lamarck The classic example used to explain the concept of use and disuse is the elongated neck of the giraffe. According to Lamarck's theory, a given giraffe could, over a lifetime of straining to reach high branches, develop an elongated neck. A major downfall of his theory was that he could not explain how this might happen, though he discussed a "natural tendency toward perfection."

Darwin’s thoughts

Natural Selection - The theory holding that competition exists within species, determining which species live to have offspring, and pass their traits on to those offspring.

Gregor Mendel Monk Born 1822

Mutations are mistakes in the DNA when it is being copied. Most mutations have no effect on the organism. If they do have an effect, they are usually harmful. Very very rarely, they might cause a change that makes the organism better at surviving. If the mutation is in the organism’s sex cells, it can be passed on to its offspring.M