What is the origin of instictive behavior to care for our kin?

Single celled organisms do not, in general, care for their offspring. Neither, in fact, do most multicellular organisms (seen a tree looking after a sapling recently?) or most animals (fish? tapeworms? coral? most turtles?). In fact, looking after your offspring is a strategy isolated to a relatively small proportion of living things. Those livings take a varying degree of care for their offspring: we support our offspring for getting on for two decades in many societies, whereas a seahorse male merely incubates the eggs until release.Offspring carers evolved from non-offspring carers, first through by providing short term, mild care and later by more and more complex caring behaviour. Each change providing an incremental benefit to their fitness.Edited by Mr Jack, : No reason given.

I don't think that's true. The many species that scatter their young to the currents generally produce very, very small undeveloped young that are highly disposable. In fact, if anything, the opposite is true: cared for young represent a much larger investment of energy than scattered young. The two approaches are referred to as K- and r- strategies, but I can't remember right now which is which. I shall look it up tomorrow.

Isn't that a change of position from your first post?I think if you plotted them both graphically, you'd determine that the very largest animals do, indeed, care for their young (see, blue whales) and the very smallest do not. This part of the pattern makes sense, it's much more difficult for a microscopic organism to effectively care for young both in terms of the advantage it can give, and the requisite behavioual repetoire to provide that care. Conversely, if you want to be very, very large it's going to be easier to get part way there, right?But in the middle there would be a huge spread of animals in which no clear pattern occurs. There are certainly plenty of large animals that do not care for their young, and small animals that do. So it seems to me that you've identified the wrong key characteristic here.Organisms which do not care for their young can produce more of them, usually massively more. If the environment allows it these organisms can massively increase their numbers in a very short time (these are r-strategists), meaning they can take advantage of highly variable environments. These environments* select for fast-growing, short lived, small body sized, early breeding, semelparous (i.e. organisms that breed only once) organisms that produce large broods.In contrast we have K-strategists. K-strategists aim to maximise their eventual population size. They cannot increase their populations so quickly, but their young are much more likely to survive and prosper. There are found in stable environments*, which select for slow-growing, large body size, late breeding, iteroparous (i.e. breeding multiple times), long lived organisms. These are also the organisms that will tend to provide maternal care.The chapter on 'Principles of Population Ecology' in Pianka's Evolutionary Ecology covers K- and r- strategists pretty well.* - w.r.t. K- and r- strategists, the environment should not be considered just as the environment in a single area. Many r-strategists also act as early colonists of new areas, whether fresh lava flows, where a tree has fallen in a forest, or whereever.