Читать книгу Your Body - The Fish That Evolved - Dr. Keith Harrison - Страница 16

This is a phrase often used by biologists, but its meaning is not immediately obvious. As Darwin noted, species compete for resources. However, it’s always easier to make a living if you have no competitors, so, if an opportunity exists in nature which is not already being exploited, something will invariably evolve to exploit it.

This is very like our commercial world today. If workers in offices are finding it hard to leave the building to buy lunch, someone will eventually set up a business making sandwiches and taking them to the offices to sell to the deskbound inmates. These sandwich entrepreneurs make their money by exploiting a gap in the market – you can probably think of dozens of similar examples. In fact, commerce is a good analogy for nature. This ‘gap in the market’ is the commercial ‘vacuum’ everyone is looking for, something they can do which no one else has thought of, where they will have a monopoly with no competitors. They can make a living while expending the minimum of effort. When others start to compete with them, they will usually try to modify their business to become more efficient (sell sandwiches that cost less to make), or provide an improved service (sell drinks as well), or branch out into new areas where they will again have no competition (sell sandwiches at construction sites), or simply try to out-compete the competition. This is Darwin’s struggle for life (in this case commercial life). Businesses therefore evolve in the same way as species evolve.

In nature, many species of bird feed on flying insects – they are a protein-rich diet – but there are also insects flying at night when birds are sleeping. Nature abhors a vacuum so this gap in the market was exploited by some nocturnal mammals which evolved wings and became bats. They even evolved wings from their front legs, just as the birds had done before them. Bats superficially resemble birds because they live in the same way.

Businesses that do the same thing will also tend to look like one another, even if they have no direct connection. This is forced upon them by the requirements of their activity. Sandwich providers on opposite sides of the world must share common features: they will use bread and sandwich fillings; they must have a facility where the sandwiches are made; they must have people making sandwiches; they must have transport to enable them to reach the offices where their customers are; they must have baskets or trolleys to carry the sandwiches; and they must handle money. These are constraints imposed upon them by their lifestyle. Nature is no different.

Animals that exploit the same gaps in the market in different parts of the world (biologists call these gaps ‘niches’) tend to resemble each other. Sea-birds in the southern hemisphere that paddle on the surface of the sea and dive for fish, swimming underwater by flapping their wings (penguins) look like sea-birds in the northern hemisphere that paddle on the surface of the sea and dive for fish, swimming underwater by flapping their wings (auks like the guillemot and razorbill). Mammals that live permanently in the water hunting fish at high speeds (dolphins) look like predatory fish that live the same way, not like other mammals. The extinct reptile ichthyosaurs also looked like dolphins and predatory fish because they shared this lifestyle – even their name means ‘fish lizards’.

Different animal groups can therefore end up mimicking each other’s bodies because they live in similar ways, even though they are not closely related. Biologists call this ‘convergent evolution’ because different animals have converged on the same body shape independently, rather than inheriting the same shape from a shared ancestor.