Generally speaking, ethical arguments against trophy or sport hunting practices frame them as exploitative and abusive against animals. Evidence has been found that wild game hunting can impact the reproductive, genetic and social health of animal species, for example by increasing aggression between species members, because hunters often kill the largest or most significant male of a species. The removal of the most significant animals (because of the size of their horns or mane for example) can affect the health of a species population. Rob Knell states that "high-quality males with large secondary sexual traits tend to father a high proportion of the offspring, their 'good genes' can spread rapidly, so populations of strongly sexually selected animals can adapt quickly to new environments. Removing these males reverses this effect and could have serious and unintended consequences. If the population is having to adapt to a new environment and you remove even a small proportion of these high quality males, you could drive it to extinction". The League Against Cruel Sports writes a "2004 study by the University of Port Elizabeth estimated that eco-tourism on private game reserves generated more than 15 times the income of livestock or game rearing or overseas hunting. Eco-tourism lodges in Eastern Cape Province produce almost 2000 rand (£180) per hectare". The U.S. House Committee on Natural Resources in 2016 concluded that trophy hunting may be contributing to the extinction of certain animals. The 25-page report is called Missing the Mark. Nnimmo Bassey, Nigerian environmental activist and director of the Health of Mother Earth Foundation, asserted in 2017 that "wildlife in Africa have been decimated by trophy hunters". Conservationist groups such as IFAW and HSUS assert that trophy hunting is a key factor in the "silent extinction" of giraffes. According to Jeff Flocken, the IFAW's analysis of CITES database, 1.7 million animals were killed by trophy hunters between 2004 and 2014, with roughly 200,000 of these being members of threatened species. Positions Trophy hunting is opposed by the group In Defense of Animals on the basis that trophy hunters are not aimed at conservation, they are instead aimed at glory in hunting and killing the biggest and rarest animals. They contend that the trophy hunters are not interested in saving endangered animals, and are more than willing to pay the very high prices for permits to kill members of an endangered species. There is an organisation