People affect animals through four broad types of activity: (1) people keep companion, farm, laboratory and captive wild animals, often while using them for some purpose; (2) people cause deliberate harm to animals through activities such as slaughter, pest control, hunting, and toxicology
testing; (3) people cause direct but unintended harm to animals through crop production, transportation, night-time lighting, and many other human activities; and (4) people harm animals indirectly by disturbing ecological systems and the processes of nature, for example by destroying habitat,
introducing foreign species, and causing pollution and climate change. Each type of activity affects vast numbers of animals and raises different scientific and ethical challenges. In Type 1 activities (keeping animals), the challenge is to improve care, sometimes by finding options that benefit
both people and animals. In Type 2 activities (deliberate harm), the challenge is to avoid compounding intentional harms with additional, unintended harms, such as animal suffering. For Type 3 and 4 activities, the challenges are to understand the unintended and indirect harms that people
cause, to motivate people to recognise and avoid such harms, and to find less harmful ways of achieving human goals. With Type 4 activities, this may involve recognising commonalities between animal welfare, conservation and human well-being. Animal welfare science and animal ethics philosophy
have traditionally focused on Type 1 and 2 activities. These fields need to include Type 3 and 4 activities, especially as they increase with human population growth.