Ontogeny is development and is usually thought of as the stages an organism goes through from zygote to adult, expressing species membership as it matures. Phylogeny is the evolutionary history of a group of organisms, a pattern of relationships among species.
Embryologist Cy Finnegan criticized the old saying, "ontogeny recapitulates phylogeny," pointing out that embryos resemble only embryos and not adult forms. In the 1800s Karl von Baer observed that the general features of vertebrate embryos appear first, followed in time by more specific group characters. Ernst Haeckel later claimed to have observed recapitulation in the organisms he studied, and extrapolated this notion to all development. Von Baer disagreed with the idea that embryos pass through the adult stages of their ancestors as they develop. Though inaccurate, the idea of recapitulation has enjoyed long popularity.
As an organism develops and reaches adulthood it takes on characteristics of its species. Developmental programs are partly based on the information captured in DNA. Humans and chimps share a lot of genetic information, so perhaps it isn't the DNA telling an organism how to develop, but the organism interpreting the information housed in its DNA. Jack Maze was looking for empirical ways to explore the relationship between development and speciation in perennial plants. Jack studied grasses, where plants die to the ground in the winter and develop new shoots and flowers each spring. He also studied conifers, where growth stops and starts seasonally.
We still don't have a very good idea of what a species is, except that it's a group of individuals that share one or more unique characteristics. Classical definitions assume that species cohesion is due to sexual reproduction, but many species of plants skip the sex, while others hybridize, having sex with plants of other species. None of our present species definitions are very good. We also lack an understanding of speciation - does an ancestral species split into two new species, or is the older species maintained? We don't know, but we do know that speciation is usually correlated with the presence of a physical barrier separating some of the populations. On the other hand, the mere presence of a barrier doesn't cause speciation.
With the elucidation of DNA, we thought all of this would become clear, but DNA is a language we are still not able to read. We don't know how we get from DNA to organisms; we have no theory of morphogenesis. Genetics and molecular biology have discovered many things, but genetic modification of organisms is mostly shooting in the dark. We need more basic research, but this is at odds with the tendency of modern universities to ape and gratify for-profit corporations under all circumstances, forgetting that their goal is education and the advancement of knowledge.