Why did people lived very long ago think that there were only two types of living things-animals and plants?

People living very long ago classified living things into two main categories—animals and plants—because their observations were primarily based on visible characteristics and behaviors. They noticed that animals were generally mobile, consumed food, and exhibited behaviors like movement and reproduction, while plants were stationary, rooted in place, and produced their own food through photosynthesis. This binary classification simplified the complex diversity of life they encountered, as they lacked the scientific tools and understanding to recognize other forms of life, such as fungi and microorganisms.