Aristotle was much concerned with teleological behavior and principles, and indeed so are human beings, most of whose conscious actions are somehow inspired and directed by some conception of an end it is supposed to be in aid of.

Indeed, very much of scientific, especially physical, chemical and biological subjects, was for many centuries mostly teleological: Living and non-living things were supposed to serve purposes and ends, that in the end were foreordained by divine foreknowledge, love and understanding, that also aimed - as e.g. Leibniz assured his readers - at "the best possible world" of all possible worlds, and indeed, being divine and infinitely powerful, also succeeded in producing just that, deo gratias (Auschwitz or not, though Leibniz knew only of many other evils, and not yet of the just named divine deeply loving end).

One problem with this mode of reasoning is that it is often adequate for human beings, who are capable, mostly thanks to their gift of language, to cooperate for ends on the basis of agreement and shared beliefs, values, knowledge and practices, and the development of plans, but less or not adequate for other living things, that do not have the gift of language, and may do no or hardly any conscious reasoning or communication or planning at all, such as plants or insects, that yet certainly interact, and cooperate at least in a metaphorical sense, in that some of their interactions result in mutually beneficent results.

Charles Darwin was one of the first who saw his way through this jungle of possible explanations, and produced an account for the behavior and evolution of animals and other living things that was not teleological at all, or at least not on the level of the lower animals.

His explanation amounted to this: Much of the behavior and forms, limbs, capacities, ways of acting and natural niches of animals and plants have slowly evolved by trial and error through their successive generations, each of which consisted of unique individuals with some possibly unique talent that they could transmit to their offspring if and when they lived long enough to produce offspring.

And if their was any purpose, any teleology in all of this, below the level of animal that could be credibly believed to have some understanding and make some more or less conscious choices, it was due to mutual adaptation, interaction, exchange, and the result of having built slowly, through many generations, a natural environment in which species of the kind that maintained and lived in it, evolved with mutually or individually beneficent repertoires and abilities, and was not due to any natural, divine or individual plan or end at all (apart from individually satisfying individually felt needs).

That was most intelligent of Darwin to see, and also very daring to publicly propose, and it was the foundation of very much the science of biology - but ever since then most men, including most biologists, have praised him, adopted his theory ... and then reformulated it in terms of purposes and ends human beings find so intuitive and easy:

Animals, for example, are widely taken to orient all their actions according to the monumenatlly silly sort of so-called neo-Darwinism that makes all or nearly all  the acts of animals "attempts to pass on their genes" - as if an animal knows it has genes, or desires to pass these unknown entities on when it mates.

The fallacy here was exposed by Darwin himself, and is counter to Darwinism:

Those and only those animals that have received innate capacities that enable them to survive and reproduce transmit those capacities to the next generation. And since, apart from twins etc. each new born animal is unique, this enables a species to survive by producing sufficiently many families that succeed in producing offspring in the environment they live in.

However, animals generally act as they please, and not with the higher end of transmitting their genes or survival of the species in mind, which indeed are concepts only human animals can understand.

And outside books of mathematical biology, it is rare to find an explanation of evolution or animal behavior that is not, and usually quite explicitly, formulated in teleological terms, mostly derived from the supposed desire of animals to transmit their genes (where a minimally intelligent person, with some knowledge and understanding of Darwin, surmises at most a desire to mate, without any end or purpose, other than felt need or pleasure).

And the science of teleology is mostly mathematical, and has to do with notions of feedback, cybernetics, or the emergence of complex interactions from more simple patterns or routines.

This has led to considerable technological successes, but so far to few biological explanations, not because these would not be possible with the mathematics that has been evolved (in statistics, in robotics, in computing, in linear algebra, in mathematical or computational - so-called - neural networks), but because as yet it is often hardly known what are the processes, proteines, cellular and biochemical mechanisms, subtleties of membranes and what not, that may be involved.

There are some, most of which have to do with Darwin's own inspiration: The competition about scarce resources, that explains quite a lot, in a neat mathematical way also, about the growth and decline of species in various circumstances and environments.

In any case, it seems a confusion to talk teleology - "Look: two mating praying mantis! The male tries to pass on his genes! The female engages in her Electra-complex by chewing off his head! We biologists know this thanks to Darwin and Freud!" - when explaining the behavior of animals less complicated than mammals and birds at best.

And such teleology as animals seem capable of understanding and using has little or nothing to do with the survival of species, and everything with their own innate simple preferences, needs and capacities, and will generally be related to their feelings of pain and pleasure.