Is love for the birds?

The whole basis of evolutionary theory is that nothing survives without a beneficial purpose, so where does love fit into that theory? When we fall in love we become dewy-eyed, mealy-mouthed, and unable to focus; all hardly the qualities designed to foster survival amid the megafauna of the Palaeolithic savannah. You would think that the evolutionary advantage would lie in selecting the perfect mate, getting on with the breeding business and leaving it at that. Yet we, humans, spend time falling in love and we don’t all fall in love with the same type of person that might be a prototypical good breeder. So what is going on with the whole falling in love thing? Researchers claim to have found the answer by studying zebra finches.

Although the superficial similarities between zebra finches and humans are few, there are some deep correlations. Zebra finches for instance mate monogamously for life (an aspirational point for some humans even if not achieved in practice), they share the burden of parental care, and they are idiosyncratic in their mate choices (that is, there is little consensus among female finches as to what makes a desirable male finch). This makes the zebra finch a prime candidate to examine any possible benefits of “love” as a basis for choosing a mate.

Zebra finches mate monogamously for life (an aspirational point for some humans even if not achieved in practice), they share the burden of parental care, and they are idiosyncratic in their mate choices.

To study this researchers let female finches choose freely from male finches. Once the finches had paired off half of the pairs were allowed go off and breed and live as they choose. The other half of the group were separated from their chosen “loved one” and forced to pair, in a kind of arranged marriage equivalent, with another similarly lovelorn finch. The birds were then observed to see what the effects might be of having a love-based versus an arranged “marriage”.

It emerged that among the chosen pairs (the love-based couples) the survival rate of chicks was 37 per cent higher than for arranged pairs. The nests of arranged pairs also had three times as many unfertilised eggs as the love-based pairs, a greater number of eggs were buried or lost among arranged pairs, and significantly more chicks died after hatching in the arranged pairs. Most chick deaths occurred in the first 48 hours after hatching during which time male partners from arranged pairs were markedly less diligent in parenting. While arranged pair males showed the females the same amount of attention, the females in these arranged pairs were much less receptive and copulated less often.

Based on all of this, the researchers conclude that zebra finches have idiosyncratic tastes and choose mates that they find stimulating in some way but in ways that aren’t necessarily clear to an observer. That individual stimulation however serves as the basis for a parental bond that maximises the survival of their offspring and that is a clear evolutionary advantage.

It seems like those “love-birds” know what they are doing.