Mammal evolution, literally

Posted Nov 22, 2012 9:56 UTC (Thu) by man_ls (subscriber, #15091) [Link]

The resolution each species you have mentioned has is -- what it needs to survive. Or more specifically: the lowest resolution it can get away with. Birds of prey need to locate their victims from a long distance; primates need accuracy to locate tree branches when they jump. Note that horses have better eye resolution than humans overall, but do not have a central fovea with increased accuracy.

The fact is that longer development periods are present in mammals than in oviparous animals. Even marsupials have to support their offspring for a certain time before they are ready -- not so with the more primitive monotremes. I think that breasts and milk are great advancements that have allowed mammals to thrive in many environments and in harsh conditions -- for example allowing the mother to feed their offspring even when the environment is bare.

I am not trying to establish a single scale from bacteria to humans; each species is almost by definition well adapted to its environment, or it will perish. Adaptations are always amazing: albatross have a gland to secrete excess salt so they can drink sea water, condors can reportedly fly up to 10 km high, penguins thrive in the Antarctic.

But there is a measurable degree of change, or divergence from the original form. There are many species which have survived unchanged during hundreds of millions of years. Mammals, primates and humans have evolved a lot from the time of dinosaurs, changing not only morphologically but also biochemically. For a simple example compare elephant trunks, dolphin tails, bat wings and human hands. While most birds are still very similar to their dinosaur ancestors in their basic shape.