There are also some other recent intriguing observations out there that beg for a theoretical explanation. There's evidence in the mouse, for example, that the paternal genome particularly favors development of the hypothalamus, whereas the maternal genome favors development of the neocortex. I've suggested that some maternal-paternal conflicts can be seen within the individual between different parts of the brain favoring different sorts of actions. I don't have a good explanation of why that's occurring in the mouse, but I would love to know. At a broader level, perhaps these theories have something to say about the subjective experience of internal conflicts—why we sometimes have great difficulty making up our minds. If the mind were purely a fitness-maximizing computer with a single fitness function, then this paralyzing sense of indecision we often feel would make no sense. When we are forced to make a difficult decision it can sometimes consume all our energies for a day, even though we'd be better off making a decision one way or the other. Perhaps that can be explained as a political argument going on within the mind between different agents with different agendas. That's getting very speculative now, though.

In the future I'd also like to get back to plants. I've put a lot of work into thinking about plant life cycles, and the work that I did in my Ph.D. has had relatively little impact, so I'd like to go back and rethink some of those ideas. I've thought of writing a book called Sociobotany that would do for plants what Trivers, Wilson, and Dawkins did for animal behavior. Botany tends to look at the different stages in the life cycles of a plant as cooperating one with the other. But Trivers's theories of parent-offspring conflict are very relevant to understanding some odd features of seed development and the embryology of plants. One of my favorite examples of this phenomenon can be seen in the seeds of pine trees and their relatives. The seed contains multiple eggs that can be fertilized by multiple pollen tubes, which are the functional equivalent of sperm. Within the seed, multiple embryos are produced that then compete to be the only one that survives in that seed. As this happens there's very intense sibling rivalry and even siblicide going on in the seed. Because of oddities of plant reproduction, the eggs that produce those embryos are all genetically identical one to the other, so all the competition among the embryos is between the genes that they get from their fathers through the pollen tube. Because of this, I expect there to be imprinting in the embryos of pine trees.

Another interesting case is found in Welwitschia, a very odd plant that grows in the Namibian desert. Here, once again because of oddities of the plant's genetics, the egg cells are no longer genetically identical one to the other, and they compete with each other to produce the embryo that survives in that seed. Rather than waiting for the pollen tube to reach the eggs, the eggs grow in tubes up to meet the pollen tubes. There's actually a race to meet the pollen tubes growing down to meet the eggs. Fertilization occurs and then the embryos race back down into the seed to gain first access to the food reserves stored in the seed. This odd behavior was just a strange observation of plant embryologists, but I think the application of ideas of conflict between different genetic individuals gives a very pleasing explanation of why you observe this behavior in Welwitschia but not in other groups where the eggs are genetically identical to each other.

Some of these ideas also intersect with the work of evolutionary psychologists. Although I don't interact with them on a daily basis, they're very keen on my work, and I follow theirs. A true psychology has got to be an evolutionary psychology. Whether every theory that goes under the name of evolutionary psychology is evolutionarily justified is a different question, but in terms of the question whether Darwin is relevant to understanding the mind and human behavior, evolutionary psychologists have got it right. We are evolved beings and therefore our psychology will have to be understood in terms of natural selection, among other factors.