Matching Pairs Origin and evolution of lifeOnline version Theories of evolution by Isabel Pérez Cotorruelo 1 Fixism 2 Evolutionary development biology 3 Endosimbiosis theory 4 Lamarckism 5 Darwinism 6 Neutralism 7 Puntuated equilibrium 8 Neo-darwinism The reasons behind the variation within a species are mutations, genetic recombination and sexual reproduction. Most mutations are neither benefitial nor harmful for the individuals that have them, so natural selection does not affect them. Living things do not change, species always stay the same Eukariotic cells originated as a result of two different types of bacteria joining together. The evolutionary process does not always take place in a slow gradual way. Instead in many cases new species are form rapidly. Some genes act as switches for other gene groups during embrionic development. The necessity creates the organ. The acquired characteristics are transmitted to offsrping. Individuals of a species that have more favourable characteristics survive more.
