Evolution and natural selection · Grade 7
Living things today are not the same as those that lived millions of years ago. Over many generations, species change: this is evolution. Charles Darwin and Alfred Russel Wallace explained how it happens. Individuals vary, and those best suited to their environment survive and pass on their genes. This is natural selection.
Key facts
- Evolution is a change in the inherited features of a population over time. All species evolved from simple life forms that first appeared more than three billion years ago.
- Natural selection: individuals in a population vary; more are born than can survive, so they compete for food, mates and space; those best adapted are more likely to survive and reproduce; they pass on their genes; over many generations the useful feature becomes more common.
- Darwin published his theory in “On the Origin of Species” in 1859. Wallace came to the same idea at the same time.
- Evidence for evolution: fossils (the remains or traces of organisms preserved in rock), and evolution we can watch happening, such as bacteria becoming resistant to antibiotics.
- Antibiotic resistance: a mutation makes a bacterium resistant; the antibiotic kills the others; the resistant ones survive and multiply. To slow it down, only use antibiotics when needed and finish the course.
- A species becomes extinct when no individuals are left: because of new predators, new diseases, more successful competitors, changes to the environment or a disaster.
- When two populations of one species are cut off from each other, they can evolve differently until they can no longer breed together: they have become two species (speciation).