Question: Flying has evolved multiple times (bats and birds and insects, at least), but among the insects, were there multiple different achievements of flight or is there a suspected common flying insect from which all current varieties of insect flight have sprung?
Answer: This is a tricky one to answer, and currently there’s no agreement on the answer. Nevertheless, let’s have a go at answering it by first of all looking at the bat and bird example cited in the question. It might seem rather obvious that bats and birds evolved flight separately, but how do we actually know this? Well, first of all, we have an excellent set of fossils in both cases, with intermediate forms showing transition from non-flying ancestors independently in each line.
Second, we can tell by comparative anatomy of the wing. In bats, the wing consists of skin stretched across the elongated bones of the hand; in birds, the wing is made of feathers extending along the length of the arm. Because the problem is the same, but the solution is different, we can conclude that bats and birds evolved their capabilities of flight separately. (We can also of course tell this because bats are much more closely related to all other non-flying mammals than they are birds – but let’s skip this for the moment for the sake of argument!)
Can we apply the same reasoning to insects, and work out if flight evolved many times, or only once? Let’s start with the fossils.
Some of the earliest fossils of insects date from around 350 Million years ago (Mya) and contain specimens that are already well adapted for flight. We simply don’t have the fossils and the intermediate forms for insects that we have in bats and birds.
The oldest definitive insect fossil is estimated at 396-407 million years old.
This species possessed a type of jaw associated with winged insects, suggesting that wings may already have evolved at this time.
So how about comparative anatomy? Well, unfortunately 350 Mya is really a long time, and evolution has been able to refine wings in insects to such an extent that it’s not even all that easy to tell what previous anatomy they evolved from in the first place, let alone if there are any evolutionarily significant structural differences between them. Three hypotheses are that they evolved from gills, from legs, or from balance structures called ‘paranotal lobes’ on an insect’s thorax, but there is no scientific consensus on this.
So it’s rather difficult to answer this question! The hunch of the author, however, is that flight in insects probably only evolved once. Flying insects are highly dispersable, often getting themselves high into the atmosphere and being deposited some thousands of miles distant. So once flight evolved in insects, it would likely have spread very quickly. A niche for a flying insect elsewhere would likely be filled by dispersal from our original flying population, rather than a subsequent novel evolution of flight.
Question sent in by Nicole Curran from Headingly.