Getting bigger? Evolution can explain that using Cope's rule. Edward Drinker Cope saw that over time, lineages of animals grew bigger and worse than their ancestors.
Cope's rule states that through evolution, a species in certain populations will, over time, become larger and larger. According to Mark Ridley, horses were at one time, the same size as a dog and they have grown to the size we are familiar with in present times. Cope noticed that some species' fossils kept getting bigger as time went on. Cope's rule states that this development is seen in microevolution. The purpose of a species becoming larger would be to show dominance and to scare away predictors. This could also be a reason for anxiety, especially if we are not large enough in size to defend ourselves. We know that any sized person can fight, but our brain is still in evolutionary mode and sees bigger as more dominant. Also, because sometimes the smaller one knows they need to fight more to survive, smaller species tend to learn how to fight and defend themselves better. Overall, evolution wants species to appear dominant and pushes for growth.
References
Ridley, M. (n.d.). Evolution - A-Z - Cope's rule. Retrieved August 08, 2017, from http://www.blackwellpublishing.com/ridley/a-z/Copes_rule.asp
Hooper Museum. (n.d.). Cope's Rule : Is Bigger Really Better? Retrieved August 08, 2017, from http://hoopermuseum.earthsci.carleton.ca/copes/WhatisCopes.html
Jablonski, D. (1997, January 16). Body-size evolution in Cretaceous molluscs and the status of Cope's rule. Retrieved August 08, 2017, from https://www.nature.com/nature/journal/v385/n6613/abs/385250a0.html
Gotanda, K. (1970, January 01). Cope's Rule: can microevolution explain it? Retrieved August 08, 2017, from http://ecoevoevoeco.blogspot.com/2015/05/copes-rule-can-microevolution-explain-it.html
Anissimov, M., & Harris, B. (2017, July 21). What is Cope's Rule? Retrieved August 08, 2017, from http://www.wisegeek.com/what-is-copes-rule.htm
Science20. (2015, February 18). Cope's Rule: Sea Creatures Are Going To Get Bigger - And So Will You. Retrieved August 08, 2017, from http://www.science20.com/the_conversation/copes_rule_sea_creatures_are_going_to_get_bigger_and_so_will_you-153351
Benton, M. (n.d.). COPE'S RULE. Retrieved August 08, 2017, from http://palaeo.gly.bris.ac.uk/benton/reprints/2002Copesrule.html
Wikipedia (n.d). Cope's Rule. Retrieved August 08, 2017. from https://en.wikipedia.org/wiki/Cope%27s_rule
Benson, R. B., Frigot, R. A., Goswami, A., Andres, B., & Butler, R. J. (2014, April 02). Competition and constraint drove Cope's rule in the evolution of giant flying reptiles. Retrieved August 08, 2017, from https://www.nature.com/articles/ncomms4567
Hone, D., & Benton, M. (2005). The evolution of large size: how does Copes Rule work? Trends in Ecology & Evolution,20(1), 4-6. doi:10.1016/j.tree.2004.10.012
Ridley, M. (n.d.). Evolution - A-Z - Cope's rule. Retrieved August 08, 2017, from http://www.blackwellpublishing.com/ridley/a-z/Copes_rule.asp
Hooper Museum. (n.d.). Cope's Rule : Is Bigger Really Better? Retrieved August 08, 2017, from http://hoopermuseum.earthsci.carleton.ca/copes/WhatisCopes.html
Jablonski, D. (1997, January 16). Body-size evolution in Cretaceous molluscs and the status of Cope's rule. Retrieved August 08, 2017, from https://www.nature.com/nature/journal/v385/n6613/abs/385250a0.html
Gotanda, K. (1970, January 01). Cope's Rule: can microevolution explain it? Retrieved August 08, 2017, from http://ecoevoevoeco.blogspot.com/2015/05/copes-rule-can-microevolution-explain-it.html
Anissimov, M., & Harris, B. (2017, July 21). What is Cope's Rule? Retrieved August 08, 2017, from http://www.wisegeek.com/what-is-copes-rule.htm
Science20. (2015, February 18). Cope's Rule: Sea Creatures Are Going To Get Bigger - And So Will You. Retrieved August 08, 2017, from http://www.science20.com/the_conversation/copes_rule_sea_creatures_are_going_to_get_bigger_and_so_will_you-153351
Benton, M. (n.d.). COPE'S RULE. Retrieved August 08, 2017, from http://palaeo.gly.bris.ac.uk/benton/reprints/2002Copesrule.html
Wikipedia (n.d). Cope's Rule. Retrieved August 08, 2017. from https://en.wikipedia.org/wiki/Cope%27s_rule
Benson, R. B., Frigot, R. A., Goswami, A., Andres, B., & Butler, R. J. (2014, April 02). Competition and constraint drove Cope's rule in the evolution of giant flying reptiles. Retrieved August 08, 2017, from https://www.nature.com/articles/ncomms4567
Hone, D., & Benton, M. (2005). The evolution of large size: how does Copes Rule work? Trends in Ecology & Evolution,20(1), 4-6. doi:10.1016/j.tree.2004.10.012