scientists to disprove this theory since they could observe that large muscles from hard work and exercise are not passed on to offspring In 1858 Englishmen Charles Darwin and Alfred Russel Wallace independently proposed the theory of evolution through natural selection In their theory survival and reproduction were the mechanisms through which change occurred Darwin explained that individuals within a species could have a number of diverse traits These traits would make some animals faster or better able to blend in with the landscape than others The animals with beneficial traits for their environment would survive longer and perhaps because of this have more offspring Many of these offspring would inherit the beneficial traits survive reproduce and pass the traits on to their own offspring As this happened through several generations the positive traits would be present in more individuals and the less beneficial traits would slowly disappear As certain traits became more common and others died out the species evolved Darwin understood that these changes happened but he did not know exactly how It would take Gregor Mendel's discovery of heredity in 1866 to explain how these changes took place Scientists later learned that heredity is caused by genes in DNA Genes are the information encoded in DNA They pass from parent to offspring They determine traits such as what color an animal's fur is or how much muscle it can build Scientists eventually realized that
According to Darwin's theory traits such as cheetahs speed helped them survive and pass on those traits to offspring change could happen as the result of a mutation A mutation is when the structure of a gene is accidentally changed because proteins or other molecules are substituted for others during reproduction A beneficial mutation could assure better success in survival and reproduction and slowly spread through the population Bad mutations make the animal more likely to die early and less likely to reproduce Over millions of years descendants of relatives of J. sinensis evolved into human beings cats and even whales If a new trait develops throughout an entire species the species as a whole evolves Sometimes the populations of a species are divided into two or more geographically separated groups This might happen when the sea level rises and floods a land bridge Ora river might cut a new channel creating an island on which part of the species lives Groups that are separated cannot interbreed Because of this one group will change in one way while another changes in another way Eventually the two groups will be so changed that they will become different species This process is how the ancestral mammals similar to J. sinensis eventually evolved into the more than 6,000 species of modern mammals
MAMMALS DEFINED Mammals are animals that share certain features First they can maintain stable body temperatures internally unlike reptiles A reptile must rely on a cool burrow to lower its temperature on a sunny day If it is too cold a reptile has to find a patch of sunlight or other warm place to raise its temperature Mammals bodies maintain a nearly constant temperature with the help of the hypothalamus a gland in the brain Nerve impulses from the skin as well as blood travel to the hypothalamus When the blood temperature or nerve impulses show that the animal is overheating the animal pants or sweats Water evaporates and the mammal cools off A mammal that is too cold can shiver to warm up Goose bumps slow air flowing across the skin reducing heat loss Both cooling off and heating up use a lot of energy Mammals get their name from a set of organs called mammary glands When a female mammal gives birth mammary glands produce milk made up of water carbohydrates fats protein minerals and disease fighting antibodies Young mammals nurse feeding on this milk Most young mammals are born live They don't hatch from eggs The exceptions to this are monotremes which include platypuses and echidnas Monotremes lay eggs Marsupials and placental mammals bear live young
CLASSIFICATION Red Fox Vulpes vulpes DOMAIN Eukaryota This domain includes plants animals and fungi These organisms are grouped together because their cells each have a nucleus a cell structure that contains the DNA KINGDOM Animalia All animals including mammals and insects are in this group PHYLUM Chordata Organisms in this phylum have a nerve cord down their backs supported by a rod of cartilage at some point in life All animals with spines including mammals and fish are in this group CLASS Mammalia This includes all mammals from cats and dogs to people and whales that nurse their young ORDER Carnivora These animals typically eat meat and have teeth specialized for this purpose FAMILY Canidae This group of generally medium sized omnivorous animals includes wolves dogs foxes and jackals GENUS Vulpes This genus includes foxes such as red foxes Arctic foxes and fennec foxes SPECIES vulpes Red foxes are the largest species of fox Taxonomic classification is the science of identifying living things grouping them together and naming them When this is done each organism is assigned a place in eight different categories ranging from domain the most general category to species the most specific category When the scientific name of an animal is given it includes the genus which is capitalized and the species which is not Red foxes are Vulpes vulpes Scientific names are often abbreviated after first use V. vulpes
