Evolution by means of Natural Selection

How old is Life on Earth?

Evolutionary Tree of Life on Earth

Evolutionary Tree of Mammals

There is a huge variety of living organisms alive today. The fossil record suggests that the number of species alive today represents around 10% of the total that have ever existed. Most species that have ever existed are now extinct. Living things have been present on Earth for around 3-4 billion years. The fossil record and the similarities between extant organisms suggest that evolution is a slow but gradual process of change and divergence.

Evolutionary Tree of Primates

Evolutionary Tree of Hominids

Evolution What causes evolution to happen?

Charles Darwin developed the theory of evolution by means of natural selection. Alfred Wallace also developed a very similar theory at the same time. Charles Darwin

The Four Steps of Natural Selection 1.There is genetic variation within a species. This variation can be due to mutations (which make new genes) or sexual reproduction (which mixes up genes). 2.Most offspring die young, before they can reproduce. They die from predation, disease or competition for resources because they are genetically “weak” (i.e. not so well adapted to their environment). 3.The best individuals, who are genetically “fit” (i.e. well adapted to their environment) live long and reproduce often, passing their good genes on to their offspring. This is the selection stage. 4.This selection is repeated each generation. After very many generations the characteristics of a whole species can change. Copy & highlight key words as you go

Final paragraph of “The Origin of Species” It is interesting to contemplate an entangled bank, clothed with many plants of many kinds, with birds singing on the bushes, with various insects flitting about, and with worms crawling through the damp earth, and to reflect that these elaborately constructed forms, so different from each other, and dependent on each other in so complex a manner, have all been produced by laws acting around us. These laws, taken in the largest sense, being Growth with Reproduction; Inheritance which is almost implied by reproduction; Variability from the indirect and direct action of the external conditions of life, and from use and disuse; a Ratio of Increase so high as to lead to a Struggle for Life, and as a consequence to Natural Selection, entailing Divergence of Character and the Extinction of less-improved forms. Thus, from the war of nature, from famine and death, the most exalted object which we are capable of conceiving, namely, the production of the higher animals, directly follows. There is grandeur in this view of life, with its several powers, having been originally breathed into a few forms or into one; and that, whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved.

Homework Question 4 from page 217

Darwin’s finches Whilst working in the Galapagos Islands, Darwin noted the different species of finch living on different islands. He also noted that food sources for these finches differed from island to island. He suggested that all the species had evolved from one ancestral type, originally from South America.

Investigating Natural Selection Imagine you are a Galapagos Finch. You can have a small, medium or large beak and you can live on an island with mainly small, medium or large seeds to eat. Using each size of “beak” record how many of each size of seed you can pick up in 30s. Which birds will be most successful and therefore selected by the environment on which islands?