Question

Fish, amphibians, reptiles, birds, and mammals have similar embryos. They all start with gill slits. Fish and some amphibians grow to have gills. Some amphibians, reptiles, birds, and mammals develop lungs to breathe air. They all start with tails. Fish, some amphibians, reptiles, and birds grow tails. Humans do not keep their tails. Fish and reptiles develop scales. Amphibians, birds, and humans have skin. Birds have feathers, and humans have hair. Which two animals exhibit the most linear relationship

Answer 1

Are you sure its not birds and humans?

Answer 2

In the context of embryonic development and characteristics that you described, fish and amphibians exhibit the most linear relationship. Both groups share several developmental traits, such as starting with gill slits and having a tail during early embryonic stages. Additionally, both fish and amphibians are tied to aquatic environments for part of their life cycle (fish as fully aquatic and amphibians typically starting their life in water). Their similarities in early development and transition from gills to lungs in adults create a straightforward evolutionary relationship, showing a clear line of descent.